- Email: [email protected]
Numerical simulation of charge transport layer free perovskite solar cell using metal work function shifted contacts
Journal Pre-proof Numerical simulation of charge transport layer free perovskite solar cell using metal work function shifted contacts Jaya Madan, Sparsh Garg, Kartavya Gupta, Shivam Rana, Aanchal Panday, Rahul Pandey
PII:
S0030-4026(19)31544-X
DOI:
https://doi.org/10.1016/j.ijleo.2019.163646
Reference:
IJLEO 163646
To appear in:
Optik
Received Date:
6 August 2019
Accepted Date:
14 October 2019
Please cite this article as: Madan J, Garg S, Gupta K, Rana S, Panday A, Pandey R, Numerical simulation of charge transport layer free perovskite solar cell using metal work function shifted contacts, Optik (2019), doi: https://doi.org/10.1016/j.ijleo.2019.163646
This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version will undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing this version to give early visibility of the article. Please note that, during the production process, errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain. © 2019 Published by Elsevier.
Numerical simulation of charge transport layer free perovskite solar cell using metal work function shifted contacts Jaya Madan1, Sparsh Garg2, Kartavya Gupta2, Shivam Rana2, Aanchal2 and Rahul Pandey1* 1
VLSI Centre of Excellence, Chitkara University Institute of Engineering and Technology, Chitkara University, Punjab, India Chitkara University Institute of Engineering and Technology, Chitkara University, Punjab, India E-mail: [email protected] 2
of
ABSTRACT
lP
re
-p
ro
Perovskite solar cells (PSCs) are one of the fastest emerging photovoltaic (PV) technology at the research level. To achieve higher conversion efficiencies from PSCs, a perovskite absorber layer is stacked between two charge transport layers (CTLs) such as electron and hole transport layers. However, fabrication of defect-free multi-layered PSC is a challenging task, and the presence of CTL and their corresponding interfaces with perovskite enhances the recombination, hysteresis and led to poor stability. Here, in this work, CTL free (i.e., electron and hole transport layer free) PSC is simulated using metal work function shifted contacts. The device presented in this work is free from transport layers and the collection process is with the help of an electric field across the perovskite layer. The electric field is created by using two metals of different work function, i.e., 4.35eV and 5.25eV (can be realized using self-assembled monolayers technique) used as cathode and anode respectively. Simulated CTL free PSC exhibits JSC=17.8 mA.cm-2, VOC=712 mV, FF=68.5% and PCE=8.7% with 250 nm thick perovskite absorber layer having bulk defect density of 2.5x1013 cm-3. Further, a comprehensive study is done in terms of front electrode work function (FEW), front electrode transparency, perovskite thickness and bulk defect density to understand the impact of these parameters on the performance of the device. To understand the behavior of the device, the energy band diagram profile is examined. Reported results show that higher metal work function difference between front and back electrode, higher transparency, and thick perovskite layer with low defect density results in better PV effect in CTL free PSC. Optimized CTL free PSC device delivers JSC=19.9 mA.cm-2, VOC=726 mV, FF=66.8% and PCE=9.7%. The design simulated in this work opens up a new window for next-generation interface defect and hysteresis-free PSC.
ur na
Keywords — Perovskite solar cell, absorption, charge transport layer, transparency, metal work function, simulation, SCAPS-1D. I. INTRODUCTION
In recent times, devices that operate on renewable sources of energy have gained immense popularity as their application increases. Solar energy is one of the ideal sources of energy [1-3]. Photovoltaic (PV) cells change
Jo
sunlight energy into electrical energy with the help of absorption of photons incident on the active material of the cell. The absorption of energy causes a generation of electron-hole pairs and the existing electric field, due to the junctions, causes a separation of charges and current begins to flow. Semiconducting materials are used as the active layer in solar cells, and among all the semiconducting material the most commonly used material for solar cells had been silicon due to its excellent properties for converting light energy to electrical energy [4, 5]. However, there are some inherent issues associated with silicon solar cells such as low absorption coefficient, the requirement of highquality material and the cost [6-9]. Researchers have discovered organic-inorganic halide perovskite materials to be used for PV applications. It shows some desirable properties for the solar cell material such as high absorption coefficient, high dielectric constant, variable and tune-able bandgap [10-13]. These properties correspond to those of
2
crystalline silicon and the material has been noted to be low-cost solution processable. The intriguing growth of inexpensive and viable PSC reported 3.8% efficiency in 2009 (first PSC) and 22.8% reported in 2018 that is near silicon record efficiency (i.e., 26.6%) and the race is still on [14]. No solar technology has ever advanced this quickly and this breakthrough record is setup by employing thin-film perovskite in the solar cell as absorber/active layer. The PSC architecture contains an active layer and two transport layers. Perovskite layer is placed between the layer of electron and hole transport materials that helps in extracting electron and hole pairs that were generated by photons. The photons are absorbed by the perovskite layer, whereas the electron-transport layer (ETL) and holetransport layer (HTL) links with the carrier generation region with electrodes [15]. Apart from being advantageous, these transport layers cause some challenges, since the fabrication of defect-free multi-layer devices is challenging.
of
In addition to this, the presence of the CTL and their respective CTL/perovskite interface enhances the recombination, hysteresis, and poor stability in perovskite devices [16-19]. Therefore, the objective of this work is to design and investigate a single layer PSC without using CTLs (such as ETL and HTL). The design utilizes the
ro
electric field across the perovskite layer to navigate the electron and hole towards opposite electrodes without the need of transport layers. The electric field is created by using two metals of different metal work function, and the
-p
device has been studied and analyzed using one-dimensional numerical simulation tool. A comprehensive study in terms of FEW, front electrode transparency, perovskite thickness and bulk defect density has been done to
re
understand the impact of these parameters on the performance of the device. II. DEVICE ARCHITECTURE AND MODEL DESCRIPTION
lP
SCAPS-1D solar cell simulator developed at the Department of Electronics and Information Systems (ELIS) of the University of Gent-Zwijnaarde, Belgium, is used to simulate the optoelectronic behavior of the device [20-22]. CTL free PSC simulated in this work is shown in Fig 1(a). It is a one- dimensional device having a single perovskite
ur na
(CH3NH3PbI3) layer with the thickness of 250 nm. CTL-free PSC is made by placing two direct gold contacts with the perovskite [16]. Xiongfeng et al. have successfully realized two gold contacts with the work function of 4.35eV and 5.25eV; authors shifted the gold work function with the help of self-assembled monolayers technique [16]. Therefore, simulation work reported in this work directly uses the two different gold contacts with the work function of 4.35eV and 5.25eV to achieve appropriate band bending. Material parameters for perovskite layer is shown in
Jo
Table I, and optical properties, i.e., the absorption coefficient is obtained using inbuild square root at Eg model in SCAPS [23].
(h ) 0 0
E g h 1 h E g
and (h ) 0
for h Eg
Where 0 =105 cm-1 and 0 =10-12 cm-1 have been used during simulations. Generated wavelength-dependent absorption coefficient data is depicted in Fig. 1(b). Further, neutral type defect is used with Gaussian distribution having characteristic energy of 0.1eV, and situated in the middle of the bandgap.
3
TABLE I Material Parameters Used in Simulation [5, 24].
Value 250 (unless otherwise mentioned) 6.5 3.9 1.55 2.2x1018 1.8x1019 2 2 1x1013 1x1013 2.5x1013 (unless otherwise mentioned) 1x105 and 1x107
ur na
lP
re
-p
Parameter Thickness (nm) Permittivity Electron affinity (eV) Band gap (eV) Effective density of state in the conduction band (cm-3) Effective density of state in the valence band (cm-3) Electron mobility (cm2V-1s-1) Hole mobility (cm2V-1s-1) Acceptor concentration (cm-3) Donor concentration (cm-3) Defect density (cm-3) Front contact surface recombination velocities (cm.s-1) for electrons and holes Back contact surface recombination velocities (cm.s-1) for electrons and holes
ro
of
(a) (b) Fig. 1: (a) The CTL free PSC; metal work function 4.35eV and 5.25eV have been used for front and back contacts, respectively and (b) absorption coefficient used in simulations, the data is obtained using inbuild square root at Eg model in SCAPS simulator.
1x107 and 1x105
III. RESULTS AND DISCUSSIONS
Result section is divided into four subsections; viz. A, B, C and D. Subsection A, B, C and D deals with the
Jo
comprehensive study of front electrode metal work function, transparency of the front electrode, impact of perovskite thickness and defect variation at different perovskite thicknesses, respectively, on the performance of CTL free PSC (Supplementary files).
A. Effect of front electrode metal workfunction In conventional PSCs, after illumination, electron-hole pairs are generated inside the perovskite layer. Further generated electron-hole pair diffuse toward the collecting interface where electron and hole are separated and collected in ETL and HTL respectively. The collection process is due to the associated electric field at the ETL/perovskite and perovskite/HTL interface. The device presented in this work is free from transport layers and the
4
collection process is with the help of an electric field across the perovskite layer. The electric field is created by using two metals of different work function. Higher the difference between metal work function, higher will be the electric field across perovskite and better will be the collection of generated carriers. To validate the statement, results are obtained by varying front electrode work function (FEW) from 4.35eV to 5.25eV while keeping the work function of the back electrode fixed at 5.25eV. Energy band diagram along with PV parameters such as JSC, VOC, FF and PCE has been obtained at different FEW and are reported in Fig. 2 (a-j) and Fig. 3(a-d), respectively. Results show the higher slope of the conduction band and valence in the case of FEW of 4.35eV, and the slope reduces as the FEW approaches to the work function of the back electrode (set at 5.25eV). Higher slope reflects a higher electric field across the perovskite layer and uplifts the carrier collection, which further reflects superior PV performance, as
of
shown in Fig. 3(a-d). Increasing FEW decreases the work function difference between the front and back electrode and reduces the slope, as shown in Fig. 2(a-j). As the difference between electrode work function decreases energy band tends to become flat due to low or absence of an electric field across the perovskite layer. Flattening of the band
ro
leads to a reduction in PV parameters, as depicted in Fig. 3(a-d) and the reduction is attributed to lower or no carrier
Jo
ur na
lP
re
-p
collection in the external circuit. It is observed that the PV effect is absent for FEW > 5.15eV.
Fig. 2: Energy band diagram of CTL free PSC at different FEW: (a) 4.35eV, (b) 4.45eV, (c) 4.55eV, (d) 4.65eV, (e) 4.75eV, (f) 4.85eV, (g) 4.95eV, (h) 5.05eV, (i) 5.15eV (j) 5.25eV. Data are obtained under illumination with short circuit condition.
ro
of
5
-p
Fig. 3: PV parameters of CTL free PSC with different FEW: (a) JSC, (b) VOC, (c) FF and (d) PCE
re
B. Impact of Transparency of the front electrode
After analyzing the impact of FEW, transparency analysis has been done, keeping in mind that the whole coverage of the front surface with non-transparent contact will not allow the coupling of photons inside the
lP
perovskite layer. Therefore, to emulate the front electrode with different transparency, transparency of the front electrode has been varied during the simulation. Performance of the device with different front electrode transparency is examined with the help of electron-hole concentration, energy band diagram, EQE, and current
ur na
density-voltage (J-V) curve and related results are reported in Fig. 4a, Fig.4b, Fig.5a, and Fig.5b, respectively. Increasing the transparency increases the optical coupling of photons inside the perovskite layers, which further results in enhanced light generated electron-hole carrier concentration as depicted in Fig. 4a. The result shows significant improvement in carrier concentration inside the perovskite layer as transparency increased from 5% to 100%. The elevated carrier concentration is also supported with the help of the energy band diagram of the device
Jo
under illumination with short circuit condition. Electron and hole quasi-Fermi energy level is obtained with two different transparency, i.e., 5% and 100% and is reported in Fig. 4b, along with conduction (EC) and valence band (EV). The band diagram depicted in Fig. 4b reflects that electron/hole quasi fermi level moves close to the conduction/valence band while transparency is improved from 5% to 100%. This also validates higher electron and hole concentration inside the wafer with higher transparency of the front electrode, as shown in Fig. 4a. PV performance, i.e., EQE and J-V curve, are also obtained and are illustrated in Fig. 5a and Fig. 5b respectively. Fig. 5a shows the EQE under different transparency, i.e., 5% to 100% in 7 equal steps. The EQE increases with an increase in transparency. Fig. 3b shows that current density increases with an increase in transparency. The improvement is due to improved optical coupling (Fig.4(a-b)) inside the perovskite layer.
of
6
ur na
lP
re
-p
ro
Fig. 4: Impact of front electrode transparency on (a) Electron concentration and (b) Energy band diagram with different T level on CTL free PSC. T is the transparency of the front electrode.
Fig. 5: Impact of front electrode transparency on CTL free PSC: (a) EQE and (b) J-V curve with different T level. T is the transparency of the front electrode.
C. Impact of perovskite thickness
In this subsection, the thickness of the perovskite layer (CH3NH3PbI3) in CTL free PSC is varied from 50 nm
Jo
to 350 nm, and the corresponding EQE and J-V curve are obtained as depicted in Fig. 6a, and Fig. 6b, respectively. Absorbance in a layer directly depends on the absorption coefficient and the thickness of the material [25] and hence, EQE of the device increases with thickness of the active (perovskite) layer up to 350 nm shown in Fig. 6a. Moreover, the increase in EQE is significant at lower thicknesses than higher thicknesses. The change in EQE at higher thicknesses is very less, attributed to absorption saturation. However, at lower thicknesses, the increment is significant. J-V curve, as reported in Fig. 6b shows that JSC and VOC increase for thick perovskite layer and the increment in JSC is substantial due to higher absorption in the thick perovskite layer. Moreover, PV parameters, i.e., JSC, VOC, FF, and PCE with different perovskite thicknesses, are also summarized in Fig. 6 (c-f). The JSC, VOC increases while increasing the thickness, whereas FF initially increases and
7
then start decreasing when the thickness is increased beyond 150 nm. The increment in Jsc and VOC is attributed to large electron-hole concentration and their subsequent separation, whereas reduction in FF is due to the reduction in the strength of electric field across the perovskite layer. Summarizing this subsection, at a higher thickness of perovskite, increment in JSC and VOC is sufficient to mitigate the reduction in FF, therefore overall PCE increases as
-p
ro
of
shown in Fig. 7(f).
re
Fig. 6: (a) EQE and (b) J-V curve of the CTL free PSC with different perovskite thickness. PV parameters: (c) JSC, (d) VOC, (e) FF and (f) PCE at different perovskite thickness. Defect density is fixed at 2.5x1013 cm-3.
D. A comprehensive study of defects at different perovskite thicknesses:
lP
The motivation of the last results section is to understand the influence of bulk defect density on PV parameters of CTL free PSC at different perovskite thicknesses. Thickness is varied from 50 nm to 350 nm in 7 equal steps and defect density is varied from 2.5x1013 cm-3 to 2.5x1017 cm-3 in 10 equal steps in log scale. Combining both
ur na
the variations, 70 batches are solved to obtain PV parameters as reported in Fig. 7(a-d). Increasing the bulk defect inside a material decreases the carrier lifetimes and hence their diffusion length, which consequently leads to higher recombination rate and low carrier collection rate. Herein, an analysis has been projected, which predicts the performance of thin and slightly thick perovskite layer with different bulk defect densities. The ultimate aim of the PV device is to collect all the light generated carrier; however, in reality, it is not possible due to several collection
Jo
and recombination losses. After illumination, subsequently generated electron-hole pair diffuse toward the collecting interface where electron and hole are collected in ETL and HTL respectively. In thin (<150 nm) perovskite layerbased solar cell relatively low diffusion is required to arrive at collecting interface and hence the performance, i.e., PV parameters such as JSC, VOC, FF, and PCE is nearly independent on the defect density inside the perovskite layer. Said variation can be valued from Fig. 7 (a-d) that the performance remains unaltered while increasing the defect from 2.3x1013 cm-3 to 2.3x1017 cm-3 at lower thicknesses of the perovskite layer. Counterpart, i.e., in slightly thick (200 nm-350 nm) perovskite layer-based device, generated carrier required to cover a large diffusion length to arrive at collecting interface and hence material quality plays a significant role. Required diffusion length is large in 200 nm-350 nm thick PSC compared to <150 nm thick PSC, and to travel the required diffusion length, high quality (less
8
defect density) material is required. Results, as reported in Fig. 7(a-d) depicts that to achieve higher conversion efficiency from 200 nm-350 nm thick perovskite solar cell, the defect density must be as low as possible. Since higher defect density will reduce the diffusion length of the carrier and will lead to a significant reduction in PV performance, as shown in Fig. 7(a-d). In this subsection, with the help of results reported in Fig. 7(a-d) it is summarized that thin, i.e., <150 nm thick PSCs are immune to bulk defect whereas thick, i.e.,>200 nm thick PSCs are vulnerable to bulk defect density. Apart from defect immunity of thin PSC, it suffers from low absorption losses since thin perovskite layer is incapable of absorbing the significant number of photons. This leads to a reduction in JSC and VOC as well. Therefore, > 250nm thick PSC is required with superior (less defected) material quality in order to boost the conversion efficiencies. This section concludes a 350 nm thick perovskite solar cell which delivers
Jo
ur na
lP
re
-p
ro
of
JSC=19.9 mA.cm-2, VOC=726 mV, FF=66.8% and PCE=9.7%.
Fig. 7: PV parameters: (a) JSC, (b) VOC, (c) FF, and (d) PCE with a combined variation of thickness and defect density. Thickness is varied from 50 nm to 350 nm and defect density is varied from 2.5x1013 cm-3 to 2.5x1017 cm-3. Combining both the variations 70 batches are solved.
9
IV. CONCLUSION SCAPS based numerical simulation is performed for CTL free PSC using metal work function shifted gold contacts. Two different contacts are used with the metal work function of 4.35eV and 5.25eV as cathode and anode respectively. Simulated CTL free PSC exhibits Jsc=17.8 mA.cm-2, Voc=712 mV, FF=68.5% and PCE=8.7% with 250 nm thick perovskite absorber layer having bulk defect density of 2.5x1013 cm-3. Further, comprehensive study and optimization are done in terms of FEW, transparency, perovskite thickness, and bulk defect density. FEW is varied from 4.35eV to 5.25eV while keeping the work function of the back electrode fixed at 5.25eV. Results show the higher slope of the conduction band and valence in the case of FEW of 4.35eV, and the slope reduces as the FEW approaches to the work function of the back electrode which is being set at 5.25eV. Higher slope reflects a higher
of
electric field across the perovskite layer and uplifts the carrier collection, which further reflects superior PV performance. It is observed that the PV effect is absent for FEW > 5.15eV. Transparency analysis shows higher light
ro
generated carrier concentration with higher transparency level and the same is also validated with the help of energy band profile, which shows that electron quasi-Fermi/hole quasi-Fermi level moves close to conduction band/valence band at higher transparency level. The thickness and defect variation reflect that in thin (<150 nm) perovskite layer-
-p
based solar cell, PV parameters such as JSC, VOC, FF, and PCE is nearly independent on the defect density inside the perovskite layer. Counterpart, i.e., in slightly thick (200 nm-350 nm) perovskite layer-based device the required
re
diffusion length is large compared to <150 nm PSC, and to travel the required diffusion length, high quality (less defect density) material is required. The result depicts that to achieve higher conversion efficiency from 200 nm-350
lP
nm thick perovskite solar, the defect density must be as low as possible. It is summarized that thin, i.e. <150 nm thick PSCs are immune to bulk defect whereas thick, i.e.,>200 nm thick PSCs are vulnerable to bulk defect density. Apart from defect immunity of thin PSC, it suffers from low absorption losses since thin perovskite layer is incapable of absorbing the significant number of photons. This leads to a reduction in JSC and VOC as well. Therefore, > 250nm
ur na
thick PSC is required with superior (less defected) material quality in order to boost the conversion efficiencies. Optimized CTL free PSC device delivers JSC=19.9 mA.cm-2, VOC=726 mV, FF=66.8% and PCE=9.7%. The design simulated in this work opens up a new window for next-generation interface defect and hysteresis-free PSC. In future, the concept simulated in this work could be employed in different lead-free perovskite layers, additive-engineering based perovskite layers and electrode/perovskite interface quality in terms of defects and carrier
Jo
recombination can also be examined. ACKNOWLEDGMENT
The authors would like to acknowledge the members of the VLSI Centre of excellence, Chitkara University,
Punjab, India, for their continuous support during the research work done. REFERENCES [1] Solar Cells, Elsevier, 2013. [2] R. Pandey, R. Chaujar, Technology computer aided design of 29.5% efficient perovskite/interdigitated back contact silicon heterojunction mechanically stacked tandem solar cell for energy-efficient applications, Journal of Photonics for Energy, 7 (2017) 022503.
10
Jo
ur na
lP
re
-p
ro
of
[3] R. Pandey, R. Chaujar, Rear contact silicon solar cells with a-SiCX:H based front surface passivation for near-ultraviolet radiation stability, Superlattices and Microstructures, 122 (2018) 111-123. [4] M. Fischer, ITRPV 10th edition 2019- report release and key findings in, ITRPV, Penang, Malaysia 2019, pp. 1-28. [5] R. Pandey, A. Singla, J. Madan, R. Sharma, R. Chaujar, Toward the design of monolithic 23.1% efficient hysteresis and moisture free perovskite/c-Si HJ tandem solar cell: a numerical simulation study, Journal of Micromechanics and Microengineering, 29 (2019) 064001. [6] S. Jeong, M.D. McGehee, Y. Cui, All-back-contact ultra-thin silicon nanocone solar cells with 13.7% power conversion efficiency, Nature communications, 4 (2013) 2950-2950. [7] R. Pandey, A.P. Saini, R. Chaujar, Numerical simulations: Toward the design of 18.6% efficient and stable perovskite solar cell using reduced cerium oxide based ETL, Vacuum, 159 (2019) 173-181. [8] L.C. Andreani, A. Bozzola, P. Kowalczewski, M. Liscidini, L. Redorici, Silicon solar cells: toward the efficiency limits, Advances in Physics: X, 4 (2019) 1548305. [9] A. Deinega, S. Eyderman, S. John, Coupled optical and electrical modeling of solar cell based on conical pore silicon photonic crystals, Journal of Applied Physics, 113 (2013) 224501-224501. [10] A. Bera, K. Wu, A. Sheikh, E. Alarousu, O.F. Mohammed, T. Wu, Perovskite Oxide SrTiO3 as an Efficient Electron Transporter for Hybrid Perovskite Solar Cells, The Journal of Physical Chemistry C, 118 (2014) 28494-28501. [11] K.A. Bush, A.F. Palmstrom, Z.J. Yu, M. Boccard, R. Cheacharoen, J.P. Mailoa, D.P. McMeekin, R.L.Z. Hoye, C.D. Bailie, T. Leijtens, I.M. Peters, M.C. Minichetti, N. Rolston, R. Prasanna, S. Sofia, D. Harwood, W. Ma, F. Moghadam, H.J. Snaith, T. Buonassisi, Z.C. Holman, S.F. Bent, M.D. McGehee, 23.6%-efficient monolithic perovskite/silicon tandem solar cells with improved stability, Nature Energy, 2 (2017) 17009. [12] B. Chen, Z. Yu, K. Liu, X. Zheng, Y. Liu, J. Shi, D. Spronk, P.N. Rudd, Z. Holman, J. Huang, Grain Engineering for Perovskite/Silicon Monolithic Tandem Solar Cells with Efficiency of 25.4%, Joule, 3 (2019) 177-190. [13] R. Pandey, R. Chaujar, Numerical simulations: Toward the design of 27.6% efficient four-terminal semi-transparent perovskite/SiC passivated rear contact silicon tandem solar cell, Superlattices and Microstructures, 100 (2016) 656-666. [14] M.A. Green, Y. Hishikawa, E.D. Dunlop, D.H. Levi, J. Hohl-Ebinger, M. Yoshita, A.W.Y. Ho-Baillie, Solar cell efficiency tables (Version 53), Progress in Photovoltaics: Research and Applications, 27 (2019) 3-12. [15] J. Dong, J. Wu, J. Jia, L. Fan, Y. Lin, J. Lin, M. Huang, Efficient perovskite solar cells employing a simply-processed CdS electron transport layer, Journal of Materials Chemistry C, 5 (2017) 10023-10028. [16] X. Lin, A.N. Jumabekov, N.N. Lal, A.R. Pascoe, D.E. Gómez, N.W. Duffy, A.S.R. Chesman, K. Sears, M. Fournier, Y. Zhang, Q. Bao, Y.-B. Cheng, L. Spiccia, U. Bach, Dipole-field-assisted charge extraction in metal-perovskite-metal backcontact solar cells, Nature Communications, 8 (2017) 613. [17] D. Di Girolamo, F. Matteocci, F.U. Kosasih, G. Chistiakova, W. Zuo, G. Divitini, L. Korte, C. Ducati, A. Di Carlo, D. Dini, A. Abate, Stability and Dark Hysteresis Correlate in NiO-Based Perovskite Solar Cells, Advanced Energy Materials, 0 1901642. [18] J. Xiang, Y. Li, F. Huang, D. Zhong, Effect of Interfacial Recombination, Bulk Recombination and Carrier Mobility on J-V Hysteresis Behaviors of Perovskite Solar Cells: A Drift-Diffusion Simulation Study, Physical Chemistry Chemical Physics, (2019). [19] D.-H. Kang, N.-G. Park, On the Current–Voltage Hysteresis in Perovskite Solar Cells: Dependence on Perovskite Composition and Methods to Remove Hysteresis, Advanced Materials, 0 1805214. [20] M. Burgelman, J. Verschraegen, B. Minnaert, J. Marlein, Numerical simulation of thin film solar cells: practical exercises with SCAPS, in: Proceedings of NUMOS (Int. Workshop on Numerical Modelling of Thin Film Solar Cells, Gent (B), Gent. 2007, UGent & Academia Press, 2007. [21] M. Burgelman, P. Nollet, S. Degrave, Modelling polycrystalline semiconductor solar cells, Thin Solid Films, 361-362 (2000) 527-532. [22] M. Burgelman, J. Verschraegen, S. Degrave, P. Nollet, Modeling thin-film PV devices, Progress in Photovoltaics: Research and Applications, 12 (2004) 143-153. [23] M. Burgelman, Models for the optical absorption of materials in SCAPS, in: M. Burgelman (Ed.), University of Ghent, Ghent, Belgium, 2018, pp. 1-13. [24] A. Nakanishi, Y. Takiguchi, S. Miyajima, Device simulation of CH3NH3PbI3 perovskite/heterojunction crystalline silicon monolithic tandem solar cells using an n-type a-Si:H/p-type µc-Si1–xOx:H tunnel junction, physica status solidi (a), 213 (2016) 1997-2002. [25] R. Pandey, R. Chaujar, Rear contact SiGe solar cell with SiC passivated front surface for >90-percent external quantum efficiency and improved power conversion efficiency, Solar Energy, 135 (2016) 242-252.
PII:
S0030-4026(19)31544-X
DOI:
https://doi.org/10.1016/j.ijleo.2019.163646
Reference:
IJLEO 163646
To appear in:
Optik
Received Date:
6 August 2019
Accepted Date:
14 October 2019
Please cite this article as: Madan J, Garg S, Gupta K, Rana S, Panday A, Pandey R, Numerical simulation of charge transport layer free perovskite solar cell using metal work function shifted contacts, Optik (2019), doi: https://doi.org/10.1016/j.ijleo.2019.163646
This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version will undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing this version to give early visibility of the article. Please note that, during the production process, errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain. © 2019 Published by Elsevier.
Numerical simulation of charge transport layer free perovskite solar cell using metal work function shifted contacts Jaya Madan1, Sparsh Garg2, Kartavya Gupta2, Shivam Rana2, Aanchal2 and Rahul Pandey1* 1
VLSI Centre of Excellence, Chitkara University Institute of Engineering and Technology, Chitkara University, Punjab, India Chitkara University Institute of Engineering and Technology, Chitkara University, Punjab, India E-mail: [email protected] 2
of
ABSTRACT
lP
re
-p
ro
Perovskite solar cells (PSCs) are one of the fastest emerging photovoltaic (PV) technology at the research level. To achieve higher conversion efficiencies from PSCs, a perovskite absorber layer is stacked between two charge transport layers (CTLs) such as electron and hole transport layers. However, fabrication of defect-free multi-layered PSC is a challenging task, and the presence of CTL and their corresponding interfaces with perovskite enhances the recombination, hysteresis and led to poor stability. Here, in this work, CTL free (i.e., electron and hole transport layer free) PSC is simulated using metal work function shifted contacts. The device presented in this work is free from transport layers and the collection process is with the help of an electric field across the perovskite layer. The electric field is created by using two metals of different work function, i.e., 4.35eV and 5.25eV (can be realized using self-assembled monolayers technique) used as cathode and anode respectively. Simulated CTL free PSC exhibits JSC=17.8 mA.cm-2, VOC=712 mV, FF=68.5% and PCE=8.7% with 250 nm thick perovskite absorber layer having bulk defect density of 2.5x1013 cm-3. Further, a comprehensive study is done in terms of front electrode work function (FEW), front electrode transparency, perovskite thickness and bulk defect density to understand the impact of these parameters on the performance of the device. To understand the behavior of the device, the energy band diagram profile is examined. Reported results show that higher metal work function difference between front and back electrode, higher transparency, and thick perovskite layer with low defect density results in better PV effect in CTL free PSC. Optimized CTL free PSC device delivers JSC=19.9 mA.cm-2, VOC=726 mV, FF=66.8% and PCE=9.7%. The design simulated in this work opens up a new window for next-generation interface defect and hysteresis-free PSC.
ur na
Keywords — Perovskite solar cell, absorption, charge transport layer, transparency, metal work function, simulation, SCAPS-1D. I. INTRODUCTION
In recent times, devices that operate on renewable sources of energy have gained immense popularity as their application increases. Solar energy is one of the ideal sources of energy [1-3]. Photovoltaic (PV) cells change
Jo
sunlight energy into electrical energy with the help of absorption of photons incident on the active material of the cell. The absorption of energy causes a generation of electron-hole pairs and the existing electric field, due to the junctions, causes a separation of charges and current begins to flow. Semiconducting materials are used as the active layer in solar cells, and among all the semiconducting material the most commonly used material for solar cells had been silicon due to its excellent properties for converting light energy to electrical energy [4, 5]. However, there are some inherent issues associated with silicon solar cells such as low absorption coefficient, the requirement of highquality material and the cost [6-9]. Researchers have discovered organic-inorganic halide perovskite materials to be used for PV applications. It shows some desirable properties for the solar cell material such as high absorption coefficient, high dielectric constant, variable and tune-able bandgap [10-13]. These properties correspond to those of
2
crystalline silicon and the material has been noted to be low-cost solution processable. The intriguing growth of inexpensive and viable PSC reported 3.8% efficiency in 2009 (first PSC) and 22.8% reported in 2018 that is near silicon record efficiency (i.e., 26.6%) and the race is still on [14]. No solar technology has ever advanced this quickly and this breakthrough record is setup by employing thin-film perovskite in the solar cell as absorber/active layer. The PSC architecture contains an active layer and two transport layers. Perovskite layer is placed between the layer of electron and hole transport materials that helps in extracting electron and hole pairs that were generated by photons. The photons are absorbed by the perovskite layer, whereas the electron-transport layer (ETL) and holetransport layer (HTL) links with the carrier generation region with electrodes [15]. Apart from being advantageous, these transport layers cause some challenges, since the fabrication of defect-free multi-layer devices is challenging.
of
In addition to this, the presence of the CTL and their respective CTL/perovskite interface enhances the recombination, hysteresis, and poor stability in perovskite devices [16-19]. Therefore, the objective of this work is to design and investigate a single layer PSC without using CTLs (such as ETL and HTL). The design utilizes the
ro
electric field across the perovskite layer to navigate the electron and hole towards opposite electrodes without the need of transport layers. The electric field is created by using two metals of different metal work function, and the
-p
device has been studied and analyzed using one-dimensional numerical simulation tool. A comprehensive study in terms of FEW, front electrode transparency, perovskite thickness and bulk defect density has been done to
re
understand the impact of these parameters on the performance of the device. II. DEVICE ARCHITECTURE AND MODEL DESCRIPTION
lP
SCAPS-1D solar cell simulator developed at the Department of Electronics and Information Systems (ELIS) of the University of Gent-Zwijnaarde, Belgium, is used to simulate the optoelectronic behavior of the device [20-22]. CTL free PSC simulated in this work is shown in Fig 1(a). It is a one- dimensional device having a single perovskite
ur na
(CH3NH3PbI3) layer with the thickness of 250 nm. CTL-free PSC is made by placing two direct gold contacts with the perovskite [16]. Xiongfeng et al. have successfully realized two gold contacts with the work function of 4.35eV and 5.25eV; authors shifted the gold work function with the help of self-assembled monolayers technique [16]. Therefore, simulation work reported in this work directly uses the two different gold contacts with the work function of 4.35eV and 5.25eV to achieve appropriate band bending. Material parameters for perovskite layer is shown in
Jo
Table I, and optical properties, i.e., the absorption coefficient is obtained using inbuild square root at Eg model in SCAPS [23].
(h ) 0 0
E g h 1 h E g
and (h ) 0
for h Eg
Where 0 =105 cm-1 and 0 =10-12 cm-1 have been used during simulations. Generated wavelength-dependent absorption coefficient data is depicted in Fig. 1(b). Further, neutral type defect is used with Gaussian distribution having characteristic energy of 0.1eV, and situated in the middle of the bandgap.
3
TABLE I Material Parameters Used in Simulation [5, 24].
Value 250 (unless otherwise mentioned) 6.5 3.9 1.55 2.2x1018 1.8x1019 2 2 1x1013 1x1013 2.5x1013 (unless otherwise mentioned) 1x105 and 1x107
ur na
lP
re
-p
Parameter Thickness (nm) Permittivity Electron affinity (eV) Band gap (eV) Effective density of state in the conduction band (cm-3) Effective density of state in the valence band (cm-3) Electron mobility (cm2V-1s-1) Hole mobility (cm2V-1s-1) Acceptor concentration (cm-3) Donor concentration (cm-3) Defect density (cm-3) Front contact surface recombination velocities (cm.s-1) for electrons and holes Back contact surface recombination velocities (cm.s-1) for electrons and holes
ro
of
(a) (b) Fig. 1: (a) The CTL free PSC; metal work function 4.35eV and 5.25eV have been used for front and back contacts, respectively and (b) absorption coefficient used in simulations, the data is obtained using inbuild square root at Eg model in SCAPS simulator.
1x107 and 1x105
III. RESULTS AND DISCUSSIONS
Result section is divided into four subsections; viz. A, B, C and D. Subsection A, B, C and D deals with the
Jo
comprehensive study of front electrode metal work function, transparency of the front electrode, impact of perovskite thickness and defect variation at different perovskite thicknesses, respectively, on the performance of CTL free PSC (Supplementary files).
A. Effect of front electrode metal workfunction In conventional PSCs, after illumination, electron-hole pairs are generated inside the perovskite layer. Further generated electron-hole pair diffuse toward the collecting interface where electron and hole are separated and collected in ETL and HTL respectively. The collection process is due to the associated electric field at the ETL/perovskite and perovskite/HTL interface. The device presented in this work is free from transport layers and the
4
collection process is with the help of an electric field across the perovskite layer. The electric field is created by using two metals of different work function. Higher the difference between metal work function, higher will be the electric field across perovskite and better will be the collection of generated carriers. To validate the statement, results are obtained by varying front electrode work function (FEW) from 4.35eV to 5.25eV while keeping the work function of the back electrode fixed at 5.25eV. Energy band diagram along with PV parameters such as JSC, VOC, FF and PCE has been obtained at different FEW and are reported in Fig. 2 (a-j) and Fig. 3(a-d), respectively. Results show the higher slope of the conduction band and valence in the case of FEW of 4.35eV, and the slope reduces as the FEW approaches to the work function of the back electrode (set at 5.25eV). Higher slope reflects a higher electric field across the perovskite layer and uplifts the carrier collection, which further reflects superior PV performance, as
of
shown in Fig. 3(a-d). Increasing FEW decreases the work function difference between the front and back electrode and reduces the slope, as shown in Fig. 2(a-j). As the difference between electrode work function decreases energy band tends to become flat due to low or absence of an electric field across the perovskite layer. Flattening of the band
ro
leads to a reduction in PV parameters, as depicted in Fig. 3(a-d) and the reduction is attributed to lower or no carrier
Jo
ur na
lP
re
-p
collection in the external circuit. It is observed that the PV effect is absent for FEW > 5.15eV.
Fig. 2: Energy band diagram of CTL free PSC at different FEW: (a) 4.35eV, (b) 4.45eV, (c) 4.55eV, (d) 4.65eV, (e) 4.75eV, (f) 4.85eV, (g) 4.95eV, (h) 5.05eV, (i) 5.15eV (j) 5.25eV. Data are obtained under illumination with short circuit condition.
ro
of
5
-p
Fig. 3: PV parameters of CTL free PSC with different FEW: (a) JSC, (b) VOC, (c) FF and (d) PCE
re
B. Impact of Transparency of the front electrode
After analyzing the impact of FEW, transparency analysis has been done, keeping in mind that the whole coverage of the front surface with non-transparent contact will not allow the coupling of photons inside the
lP
perovskite layer. Therefore, to emulate the front electrode with different transparency, transparency of the front electrode has been varied during the simulation. Performance of the device with different front electrode transparency is examined with the help of electron-hole concentration, energy band diagram, EQE, and current
ur na
density-voltage (J-V) curve and related results are reported in Fig. 4a, Fig.4b, Fig.5a, and Fig.5b, respectively. Increasing the transparency increases the optical coupling of photons inside the perovskite layers, which further results in enhanced light generated electron-hole carrier concentration as depicted in Fig. 4a. The result shows significant improvement in carrier concentration inside the perovskite layer as transparency increased from 5% to 100%. The elevated carrier concentration is also supported with the help of the energy band diagram of the device
Jo
under illumination with short circuit condition. Electron and hole quasi-Fermi energy level is obtained with two different transparency, i.e., 5% and 100% and is reported in Fig. 4b, along with conduction (EC) and valence band (EV). The band diagram depicted in Fig. 4b reflects that electron/hole quasi fermi level moves close to the conduction/valence band while transparency is improved from 5% to 100%. This also validates higher electron and hole concentration inside the wafer with higher transparency of the front electrode, as shown in Fig. 4a. PV performance, i.e., EQE and J-V curve, are also obtained and are illustrated in Fig. 5a and Fig. 5b respectively. Fig. 5a shows the EQE under different transparency, i.e., 5% to 100% in 7 equal steps. The EQE increases with an increase in transparency. Fig. 3b shows that current density increases with an increase in transparency. The improvement is due to improved optical coupling (Fig.4(a-b)) inside the perovskite layer.
of
6
ur na
lP
re
-p
ro
Fig. 4: Impact of front electrode transparency on (a) Electron concentration and (b) Energy band diagram with different T level on CTL free PSC. T is the transparency of the front electrode.
Fig. 5: Impact of front electrode transparency on CTL free PSC: (a) EQE and (b) J-V curve with different T level. T is the transparency of the front electrode.
C. Impact of perovskite thickness
In this subsection, the thickness of the perovskite layer (CH3NH3PbI3) in CTL free PSC is varied from 50 nm
Jo
to 350 nm, and the corresponding EQE and J-V curve are obtained as depicted in Fig. 6a, and Fig. 6b, respectively. Absorbance in a layer directly depends on the absorption coefficient and the thickness of the material [25] and hence, EQE of the device increases with thickness of the active (perovskite) layer up to 350 nm shown in Fig. 6a. Moreover, the increase in EQE is significant at lower thicknesses than higher thicknesses. The change in EQE at higher thicknesses is very less, attributed to absorption saturation. However, at lower thicknesses, the increment is significant. J-V curve, as reported in Fig. 6b shows that JSC and VOC increase for thick perovskite layer and the increment in JSC is substantial due to higher absorption in the thick perovskite layer. Moreover, PV parameters, i.e., JSC, VOC, FF, and PCE with different perovskite thicknesses, are also summarized in Fig. 6 (c-f). The JSC, VOC increases while increasing the thickness, whereas FF initially increases and
7
then start decreasing when the thickness is increased beyond 150 nm. The increment in Jsc and VOC is attributed to large electron-hole concentration and their subsequent separation, whereas reduction in FF is due to the reduction in the strength of electric field across the perovskite layer. Summarizing this subsection, at a higher thickness of perovskite, increment in JSC and VOC is sufficient to mitigate the reduction in FF, therefore overall PCE increases as
-p
ro
of
shown in Fig. 7(f).
re
Fig. 6: (a) EQE and (b) J-V curve of the CTL free PSC with different perovskite thickness. PV parameters: (c) JSC, (d) VOC, (e) FF and (f) PCE at different perovskite thickness. Defect density is fixed at 2.5x1013 cm-3.
D. A comprehensive study of defects at different perovskite thicknesses:
lP
The motivation of the last results section is to understand the influence of bulk defect density on PV parameters of CTL free PSC at different perovskite thicknesses. Thickness is varied from 50 nm to 350 nm in 7 equal steps and defect density is varied from 2.5x1013 cm-3 to 2.5x1017 cm-3 in 10 equal steps in log scale. Combining both
ur na
the variations, 70 batches are solved to obtain PV parameters as reported in Fig. 7(a-d). Increasing the bulk defect inside a material decreases the carrier lifetimes and hence their diffusion length, which consequently leads to higher recombination rate and low carrier collection rate. Herein, an analysis has been projected, which predicts the performance of thin and slightly thick perovskite layer with different bulk defect densities. The ultimate aim of the PV device is to collect all the light generated carrier; however, in reality, it is not possible due to several collection
Jo
and recombination losses. After illumination, subsequently generated electron-hole pair diffuse toward the collecting interface where electron and hole are collected in ETL and HTL respectively. In thin (<150 nm) perovskite layerbased solar cell relatively low diffusion is required to arrive at collecting interface and hence the performance, i.e., PV parameters such as JSC, VOC, FF, and PCE is nearly independent on the defect density inside the perovskite layer. Said variation can be valued from Fig. 7 (a-d) that the performance remains unaltered while increasing the defect from 2.3x1013 cm-3 to 2.3x1017 cm-3 at lower thicknesses of the perovskite layer. Counterpart, i.e., in slightly thick (200 nm-350 nm) perovskite layer-based device, generated carrier required to cover a large diffusion length to arrive at collecting interface and hence material quality plays a significant role. Required diffusion length is large in 200 nm-350 nm thick PSC compared to <150 nm thick PSC, and to travel the required diffusion length, high quality (less
8
defect density) material is required. Results, as reported in Fig. 7(a-d) depicts that to achieve higher conversion efficiency from 200 nm-350 nm thick perovskite solar cell, the defect density must be as low as possible. Since higher defect density will reduce the diffusion length of the carrier and will lead to a significant reduction in PV performance, as shown in Fig. 7(a-d). In this subsection, with the help of results reported in Fig. 7(a-d) it is summarized that thin, i.e., <150 nm thick PSCs are immune to bulk defect whereas thick, i.e.,>200 nm thick PSCs are vulnerable to bulk defect density. Apart from defect immunity of thin PSC, it suffers from low absorption losses since thin perovskite layer is incapable of absorbing the significant number of photons. This leads to a reduction in JSC and VOC as well. Therefore, > 250nm thick PSC is required with superior (less defected) material quality in order to boost the conversion efficiencies. This section concludes a 350 nm thick perovskite solar cell which delivers
Jo
ur na
lP
re
-p
ro
of
JSC=19.9 mA.cm-2, VOC=726 mV, FF=66.8% and PCE=9.7%.
Fig. 7: PV parameters: (a) JSC, (b) VOC, (c) FF, and (d) PCE with a combined variation of thickness and defect density. Thickness is varied from 50 nm to 350 nm and defect density is varied from 2.5x1013 cm-3 to 2.5x1017 cm-3. Combining both the variations 70 batches are solved.
9
IV. CONCLUSION SCAPS based numerical simulation is performed for CTL free PSC using metal work function shifted gold contacts. Two different contacts are used with the metal work function of 4.35eV and 5.25eV as cathode and anode respectively. Simulated CTL free PSC exhibits Jsc=17.8 mA.cm-2, Voc=712 mV, FF=68.5% and PCE=8.7% with 250 nm thick perovskite absorber layer having bulk defect density of 2.5x1013 cm-3. Further, comprehensive study and optimization are done in terms of FEW, transparency, perovskite thickness, and bulk defect density. FEW is varied from 4.35eV to 5.25eV while keeping the work function of the back electrode fixed at 5.25eV. Results show the higher slope of the conduction band and valence in the case of FEW of 4.35eV, and the slope reduces as the FEW approaches to the work function of the back electrode which is being set at 5.25eV. Higher slope reflects a higher
of
electric field across the perovskite layer and uplifts the carrier collection, which further reflects superior PV performance. It is observed that the PV effect is absent for FEW > 5.15eV. Transparency analysis shows higher light
ro
generated carrier concentration with higher transparency level and the same is also validated with the help of energy band profile, which shows that electron quasi-Fermi/hole quasi-Fermi level moves close to conduction band/valence band at higher transparency level. The thickness and defect variation reflect that in thin (<150 nm) perovskite layer-
-p
based solar cell, PV parameters such as JSC, VOC, FF, and PCE is nearly independent on the defect density inside the perovskite layer. Counterpart, i.e., in slightly thick (200 nm-350 nm) perovskite layer-based device the required
re
diffusion length is large compared to <150 nm PSC, and to travel the required diffusion length, high quality (less defect density) material is required. The result depicts that to achieve higher conversion efficiency from 200 nm-350
lP
nm thick perovskite solar, the defect density must be as low as possible. It is summarized that thin, i.e. <150 nm thick PSCs are immune to bulk defect whereas thick, i.e.,>200 nm thick PSCs are vulnerable to bulk defect density. Apart from defect immunity of thin PSC, it suffers from low absorption losses since thin perovskite layer is incapable of absorbing the significant number of photons. This leads to a reduction in JSC and VOC as well. Therefore, > 250nm
ur na
thick PSC is required with superior (less defected) material quality in order to boost the conversion efficiencies. Optimized CTL free PSC device delivers JSC=19.9 mA.cm-2, VOC=726 mV, FF=66.8% and PCE=9.7%. The design simulated in this work opens up a new window for next-generation interface defect and hysteresis-free PSC. In future, the concept simulated in this work could be employed in different lead-free perovskite layers, additive-engineering based perovskite layers and electrode/perovskite interface quality in terms of defects and carrier
Jo
recombination can also be examined. ACKNOWLEDGMENT
The authors would like to acknowledge the members of the VLSI Centre of excellence, Chitkara University,
Punjab, India, for their continuous support during the research work done. REFERENCES [1] Solar Cells, Elsevier, 2013. [2] R. Pandey, R. Chaujar, Technology computer aided design of 29.5% efficient perovskite/interdigitated back contact silicon heterojunction mechanically stacked tandem solar cell for energy-efficient applications, Journal of Photonics for Energy, 7 (2017) 022503.
10
Jo
ur na
lP
re
-p
ro
of
[3] R. Pandey, R. Chaujar, Rear contact silicon solar cells with a-SiCX:H based front surface passivation for near-ultraviolet radiation stability, Superlattices and Microstructures, 122 (2018) 111-123. [4] M. Fischer, ITRPV 10th edition 2019- report release and key findings in, ITRPV, Penang, Malaysia 2019, pp. 1-28. [5] R. Pandey, A. Singla, J. Madan, R. Sharma, R. Chaujar, Toward the design of monolithic 23.1% efficient hysteresis and moisture free perovskite/c-Si HJ tandem solar cell: a numerical simulation study, Journal of Micromechanics and Microengineering, 29 (2019) 064001. [6] S. Jeong, M.D. McGehee, Y. Cui, All-back-contact ultra-thin silicon nanocone solar cells with 13.7% power conversion efficiency, Nature communications, 4 (2013) 2950-2950. [7] R. Pandey, A.P. Saini, R. Chaujar, Numerical simulations: Toward the design of 18.6% efficient and stable perovskite solar cell using reduced cerium oxide based ETL, Vacuum, 159 (2019) 173-181. [8] L.C. Andreani, A. Bozzola, P. Kowalczewski, M. Liscidini, L. Redorici, Silicon solar cells: toward the efficiency limits, Advances in Physics: X, 4 (2019) 1548305. [9] A. Deinega, S. Eyderman, S. John, Coupled optical and electrical modeling of solar cell based on conical pore silicon photonic crystals, Journal of Applied Physics, 113 (2013) 224501-224501. [10] A. Bera, K. Wu, A. Sheikh, E. Alarousu, O.F. Mohammed, T. Wu, Perovskite Oxide SrTiO3 as an Efficient Electron Transporter for Hybrid Perovskite Solar Cells, The Journal of Physical Chemistry C, 118 (2014) 28494-28501. [11] K.A. Bush, A.F. Palmstrom, Z.J. Yu, M. Boccard, R. Cheacharoen, J.P. Mailoa, D.P. McMeekin, R.L.Z. Hoye, C.D. Bailie, T. Leijtens, I.M. Peters, M.C. Minichetti, N. Rolston, R. Prasanna, S. Sofia, D. Harwood, W. Ma, F. Moghadam, H.J. Snaith, T. Buonassisi, Z.C. Holman, S.F. Bent, M.D. McGehee, 23.6%-efficient monolithic perovskite/silicon tandem solar cells with improved stability, Nature Energy, 2 (2017) 17009. [12] B. Chen, Z. Yu, K. Liu, X. Zheng, Y. Liu, J. Shi, D. Spronk, P.N. Rudd, Z. Holman, J. Huang, Grain Engineering for Perovskite/Silicon Monolithic Tandem Solar Cells with Efficiency of 25.4%, Joule, 3 (2019) 177-190. [13] R. Pandey, R. Chaujar, Numerical simulations: Toward the design of 27.6% efficient four-terminal semi-transparent perovskite/SiC passivated rear contact silicon tandem solar cell, Superlattices and Microstructures, 100 (2016) 656-666. [14] M.A. Green, Y. Hishikawa, E.D. Dunlop, D.H. Levi, J. Hohl-Ebinger, M. Yoshita, A.W.Y. Ho-Baillie, Solar cell efficiency tables (Version 53), Progress in Photovoltaics: Research and Applications, 27 (2019) 3-12. [15] J. Dong, J. Wu, J. Jia, L. Fan, Y. Lin, J. Lin, M. Huang, Efficient perovskite solar cells employing a simply-processed CdS electron transport layer, Journal of Materials Chemistry C, 5 (2017) 10023-10028. [16] X. Lin, A.N. Jumabekov, N.N. Lal, A.R. Pascoe, D.E. Gómez, N.W. Duffy, A.S.R. Chesman, K. Sears, M. Fournier, Y. Zhang, Q. Bao, Y.-B. Cheng, L. Spiccia, U. Bach, Dipole-field-assisted charge extraction in metal-perovskite-metal backcontact solar cells, Nature Communications, 8 (2017) 613. [17] D. Di Girolamo, F. Matteocci, F.U. Kosasih, G. Chistiakova, W. Zuo, G. Divitini, L. Korte, C. Ducati, A. Di Carlo, D. Dini, A. Abate, Stability and Dark Hysteresis Correlate in NiO-Based Perovskite Solar Cells, Advanced Energy Materials, 0 1901642. [18] J. Xiang, Y. Li, F. Huang, D. Zhong, Effect of Interfacial Recombination, Bulk Recombination and Carrier Mobility on J-V Hysteresis Behaviors of Perovskite Solar Cells: A Drift-Diffusion Simulation Study, Physical Chemistry Chemical Physics, (2019). [19] D.-H. Kang, N.-G. Park, On the Current–Voltage Hysteresis in Perovskite Solar Cells: Dependence on Perovskite Composition and Methods to Remove Hysteresis, Advanced Materials, 0 1805214. [20] M. Burgelman, J. Verschraegen, B. Minnaert, J. Marlein, Numerical simulation of thin film solar cells: practical exercises with SCAPS, in: Proceedings of NUMOS (Int. Workshop on Numerical Modelling of Thin Film Solar Cells, Gent (B), Gent. 2007, UGent & Academia Press, 2007. [21] M. Burgelman, P. Nollet, S. Degrave, Modelling polycrystalline semiconductor solar cells, Thin Solid Films, 361-362 (2000) 527-532. [22] M. Burgelman, J. Verschraegen, S. Degrave, P. Nollet, Modeling thin-film PV devices, Progress in Photovoltaics: Research and Applications, 12 (2004) 143-153. [23] M. Burgelman, Models for the optical absorption of materials in SCAPS, in: M. Burgelman (Ed.), University of Ghent, Ghent, Belgium, 2018, pp. 1-13. [24] A. Nakanishi, Y. Takiguchi, S. Miyajima, Device simulation of CH3NH3PbI3 perovskite/heterojunction crystalline silicon monolithic tandem solar cells using an n-type a-Si:H/p-type µc-Si1–xOx:H tunnel junction, physica status solidi (a), 213 (2016) 1997-2002. [25] R. Pandey, R. Chaujar, Rear contact SiGe solar cell with SiC passivated front surface for >90-percent external quantum efficiency and improved power conversion efficiency, Solar Energy, 135 (2016) 242-252.