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Performance improvement of inverted perovskite solar cells using TiO2 nanorod array and mesoporous structure
Organic Electronics 75 (2019) 105433
Contents lists available at ScienceDirect
Organic Electronics journal homepage: www.elsevier.com/locate/orgel
Performance improvement of inverted perovskite solar cells using TiO2 nanorod array and mesoporous structure
T
Ching-Ting Leea,b,c,∗, Sian-Yuan Yangb a
Department of Electrical Engineering, Yuan Ze University, Taoyuan, 320, Taiwan, ROC Institute of Microelectronics, Department of Electrical Engineering, National Cheng Kung University, Tainan, 701, Taiwan, ROC c Department of Photonics, National Cheng Kung University, Tainan, 701, Taiwan, ROC b
ARTICLE INFO
ABSTRACT
Keywords: Inverted perovskite solar cells Laser interference lithography system Mesoporous layer Nanorod array Titanium dioxide material
In view of the low carrier mobility of organic materials, the carrier collection ability was suffered from the short transport length before carriers were recombined. To improve performances by enhancing carrier collection ability, the optimal period was 1.5 μm which was obtained by changing the period of titanium dioxide (TiO2) nanorod array in the inverted perovskite solar cells (IPSCs). The power conversion efficiency was improved to 11.96% from the 7.66% of the standard planar IPSCs. Besides, due to the inherent properties of high absorption surface area and high light scattering ability, the 150-nm-thick TiO2 mesoporous layer was embedded in the TiO2 electron transport layer. By changing the annealing temperature, the optimal crystallinity of anatase phase and the optimal porous distribution were obtained in the TiO2 mesoporous layers annealed at 500 °C for 30 min. Using the optimal annealed TiO2 mesoporous layers in the IPSCs, the power conversion efficiency was improved to 12.73%. The power conversion efficiency of 14.47% was obtained for the IPSCs embedded with the optimal 1.5-μm-periodic TiO2 nanorod array and the optimal 500 °C-annealed TiO2 mesoporous layer in the electron transport layer, simultaneously.
1. Introduction Due to energy shortage and environment pollution, it is urgently needed to develop green renewable energy sources. Among the renewable energy sources, solar energy source has been substantially attracted and focused owing to its nonpollution and permanent sufficiency. In view of the inherent advantages of optical and electrical properties, the performances of organic-inorganic hybrid perovskite solar cells have been significantly improved, recently [1–8]. The perovskite solar cells become promising candidate of the organic solar cells. Because the inverted structure was designed and demonstrated to improve the performance of polymer solar cells [9,10], the inverted perovskite solar cells (IPSCs) were fabricated and studied in this work. To overcome the inherent disadvantage of short transport length of generated carriers caused by the low carrier mobility in the organic materials, the embedded nanorod array was proposed, previously [11]. Besides, owing to nontoxic, long-term durability, distinct photochemical activity, and stable chemical and physical properties, titanium dioxide (TiO2) was widely applied in dye-sensitized solar cells [12–15]. In this study, to improve performances of IPSCs, nanorod array and mesoporous structure were used to enhance carrier collection ability
∗
and to increase more exciton in active layer, respectively. The electron transport layer (ETL) of the IPSCs was constructed by TiO2 mesoporous layer/TiO2 nanorod array/TiO2 film. To study the optimal ETL structure, various annealed TiO2 mesoporous layers and various periodic TiO2 nanorod arrays were fabricated and studied. The current densityvoltage characteristics, external quantum efficiency (EQE) and dark current density of the resulting IPSCs were measured and analyzed. 2. Device fabrication experiments Fig. 1 shows the schematic configuration of the designed IPSCs. After cleaning the 200-nn-thick fluorine-doped tin oxide (FTO)-coated glass substrates using successive treatment under ultrasonic bath in acetone, methyl alcohol and deionized water, a 30-nm-thick TiO2 film was then deposited by an electron beam evaporator. The photoresist (AZ6112) was spread on the TiO2 film using a spin coater. Two-beam He-Cd laser interference photolithography system was used to perform interference grating strips [16]. After rotating an angle of 90°, the perpendicularly crossed grating patterns were defined by exposing the sample using the same process parameters. By changing the intersection angle of the two-beam He-Cd laser, various periodic photoresist
Corresponding author. Department of Electrical Engineering, Yuan Ze University, Taoyuan, 320, Taiwan, ROC. E-mail address: [email protected] (C.-T. Lee).
https://doi.org/10.1016/j.orgel.2019.105433 Received 17 June 2019; Received in revised form 8 August 2019; Accepted 24 August 2019 Available online 26 August 2019 1566-1199/ © 2019 Elsevier B.V. All rights reserved.
Organic Electronics 75 (2019) 105433
C.-T. Lee and S.-Y. Yang
Fig. 1. Schematic configuration of inverted perovskite solar cells.
patterns could be performed. After developing in developer solution for 45 s, various dimensional photoresist arrays were obtained. A 200-nmthick zinc oxide (ZnO) sacrificial film was deposited using a radio frequency magnetron sputtering system. After the photoresist array was lifted off using acetone, the perpendicularly crossed ZnO sacrificial grating structures were obtained. A 150-nm-thick TiO2 film was obliquely deposited using an electron beam evaporator. Various periodic TiO2 nanorod arrays were resulted, after the ZnO sacrificial grating structures were etched away by a chemical solution of H3PO4:H2O (2:100) at 90 °C. To form TiO2 mesoporous structure, the mixed solution of TiO2 powder (1 g), ethyl cellulose (5 g), terpineol anhydrous (0.2 mL), and ethanol (7.5 mL) was first prepared, and then the mixed solution was spread on the sample using a spin coater. To remove the residual organic materials, the sample was annealed at various temperatures. To deposit a 360-nm-thick perovskite active layer of IPSCs, the solution of methylammonium iodide (CH3NH3I, 0.40 g), lead iodide (PbI2, 1.16 g), γ-butyrolactone (GBL, 1 mL), and dimethyl sulfoxide (DMSO, 1 mL) was mixed and stirred at 70 °C for one day. By first rotating the spin coater at a speed of 1000 rpm for 10 s and then at 5000 rpm for 20 s, the mixed solution was spread on the sample. In the spreading process, a toluene was dropped on the sample at the middle spreading time to remove the uneasily volatile organic solvent [17]. Subsequently, the mixed solution of spiro-OMeTAD (80 mg), chlorobenzene solvent (1 mL), 4-tert-butylphyridine (TBP, 28.5 μL), and bis (trifluoromethane) sulfonamide lithium salt (Li-TFSI, 14.5 μL) was prepared and stirred for one day. The purpose of adding Li-TFSI was to improve the carrier mobility of spiro-OMeTAD hole transport layer (HTL) [18–20]. A 280-nm-thick spiro-OMeTAD HTL was deposited by dropping the mixed solution on the top surface of the perovskite active layer and spin-coating at 4000 rpm for 30 s. The sample was then baked at 90 °C for 5 min to remove the residual solvent. Finally, the device fabrication was completed by thermal evaporation of top silver electrode (100 nm) through shadow mask with a pressure of 4 × 10−4 Pa.
temperature until 500 °C. Based on the diffraction angle of 25.0°, the anatase phase of the annealed TiO2 crystallinity was deduced. Furthermore, the reduction of residual defects and the improvement of carrier mobility would be concluded from the enhanced peak intensity at a higher annealing temperature [21]. When the TiO2 films were annealed at 550 °C, its diffraction angle was changed to 28.0°. It was resulted that the crystallinity was changed from anatase phase to rutile phase. Using Hall measurement at a room temperature, electron concentration, electron mobility, and resistivity of the resulting TiO2 films were listed in Table 1. Due to the anatase phase and the highest peak intensity, the highest electron concentration of 8.2 × 1018 cm−3 and the highest electron mobility of 15.2 cm2/V-s were obtained in the TiO2 films annealed at 500 °C for 30 min. Besides, the crystalline properties of the TiO2 nanorods and the TiO2 mesoporous layer were assumed to be the similar crystallinity of the TiO2 film annealed at the same temperature. To observe the surface morphology, Fig. 4 (a), (b), (c), and (d) shows the scanning electron microscope images of the TiO2 mesoporous layers annealed for 30 min at 400, 450, 500, and 550 °C, respectively. It could be seen that more uniform porous distribution was formed in the TiO2 mesoporous layer annealed at 500 °C for 30 min. The current density-voltage (J-V) characteristics of IPSCs were measured at a room temperature using a J-V curve tracer under an illumination of 100 mW/cm2 with an AM 1.5G solar simulator. Fig. 5 shows the J-V characteristics of the IPSCs without mesoporous structure and with various periodic TiO2 nanorod arrays. Table 2 listed the photovoltaic characteristics of short-circuit current density (Jsc), opencircuit voltage (Voc), fill factor (FF), and power conversion efficiency (PCE). Fig. 6 shows the associated external quantum efficiency (EQE) as a function of wavelength in which was measured using a xenon lamp and a chopper with a lock-in amplifier for phase-sensitive detection. It was found that the EQE and Jsc of the IPSCs with TiO2 nanorod arrays was larger than that of those without TiO2 nanorod array. The improved performance was attributed to the increased carrier collection ability by the TiO2 nanorod array. Furthermore, the EQE and Jsc of the IPSCs increased by reducing the period of the TiO2 nanorod array. Those phenomena were attributed to the enhanced carrier collection ability, because the carrier transport length is short due to the low carrier mobility in organic materials. Therefore, before the carriers were recombined, more carriers could be collected by the cathode electrode and the anode electrode to improve EQE and Jsc in a narrower periodic TiO2 nanorod array. As listed in Table 2, Voc and FF of IPSCs decreased with a reduction of the period of TiO2 nanorod array. To study the mechanisms, the dark current density-voltage characteristics of the above-mentioned IPSCs were measured and shown in Fig. 7. It was seen that the dark current density increased with a decrease of the
3. Experimental results and discussion Fig. 2 (a), (b), and (c) shows the scanning electron microscope images of the TiO2 nanorod arrays with a period of 2.0, 1.5, and 1.0 μm, respectively. Fig. 2 (d) presents the profile of nanorod in the 2.0-μmperiodic TiO2 nanorod array measured using atomic force microscopy. It was found that the height of the TiO2 nanorod array was about 150 nm. To study the crystalline property, Fig. 3 shows the X-ray diffraction (XRD) spectra of the TiO2 films annealed at various temperatures for 30 min. It was observed that the peak intensity at the diffraction angle of 25.0° was enhanced with increasing the annealing 2
Organic Electronics 75 (2019) 105433
C.-T. Lee and S.-Y. Yang
Fig. 2. Scanning electron microscope images of TiO2 nanorod array with a period of (a) 2.0 μm, (b) 1.5 μm, and (c) 1.0 μm. (d) Atomic force microscope of 2.0 μm-periodic TiO2 nanorod array.
Fig. 3. X-ray diffraction spectra of TiO2 films annealed at various temperatures for 30 min. Table 1 Electrical properties of TiO2 films annealed at various temperatures for 30 min. Annealing temperature (oC)
Electron concentration (cm−3)
Electron mobility (cm2/V-s)
Resistivity (cm-Ω)
400 450 500 550
5.7 × 1018 6.2 × 1018 8.2 × 1018 6.2 × 1018
12.4 13.7 15.2 13.3
8.8 × 10−2 7.3 × 10−2 5.1 × 10−2 7.6 × 10−2
period of TiO2 nanorod array. Since the higher nanorod density could be obtained in a narrower periodic TiO2 nanorod array, the larger total surface area was resulted in a narrower periodic TiO2 nanorod array. The larger dark current density was contributed by the more defects resided on the larger total surface area of the tinier nanorods in a narrower periodic TiO2 nanorod array. Consequently, the Voc and FF were degraded by the existence of more defects and the larger dark current density [22]. Compared with the PCE of 7.66% of the IPSCs without TiO2 nanorod array, the PCE could be improved by using TiO2 nanorod array. By trading off the Jsc, Voc, and FF of the IPSCs, the best PCE of 11.96% was obtained by embedding 1.5 μm periodic TiO2 nanorod array. To study the optimal TiO2 mesoporous layer, the IPSCs without TiO2 nanorod array and with TiO2 mesoporous layers annealed at various temperatures for 30 min were fabricated and measured. The associated J-V characteristics and the photovoltaic characteristics were shown in Fig. 8 and were listed in Table 3, respectively. Compared with the photovoltaic characteristics without TiO2 mesoporous layer, the performances were significantly improved by using TiO2 mesoporous layer in the IPSCs. It was also found that the photovoltaic characteristics of the IPSCs were enhanced by increasing the annealing temperature until 500 °C and then decreased by further increasing annealing temperature to 550 °C. Compared with the rutile phase of the TiO2 layers annealed at 550 °C, the anatase phase of the TiO2 layers annealed at below 500 °C has better carrier mobility and conductivity as listed in Table 1 [23]. As the XRD spectra shown in Fig. 3, the crystallinity of the anatase phase of the TiO2 films was enhanced by increasing the annealing temperature to 500 °C. Besides, as the SEM images shown in Fig. 4, the more uniform 3
Organic Electronics 75 (2019) 105433
C.-T. Lee and S.-Y. Yang
Fig. 4. Scanning electron microscope images of TiO2 mesoporous layers annealed for 30 min at (a) 400 °C, (b) 450 °C, (c) 500 °C, and (d) 550 °C.
Fig. 5. Current density-voltage characteristics of inverted perovskite solar cells without mesoporous structure and with various periodic TiO2 nanorod arrays. Table 2 Photovoltaic characteristics of inverted perovskite solar cells without TiO2 mesoporous structure and with various periodic TiO2 nanorod arrays. Period (μm)
Jsc (mA/cm2)
Voc (V)
FF (%)
PCE (%)
without 3.0 2.5 2.0 1.5 1.0
15.73 19.35 21.81 23.79 25.28 26.05
0.74 0.74 0.74 0.73 0.73 0.72
65.80 65.67 65.49 65.27 65.01 63.70
7.66 9.40 10.52 11.38 11.96 11.88
Fig. 6. External quantum efficiency of inverted perovskite solar cells without mesoporous structure and with various periodic TiO2 nanorod arrays.
porous distribution was obtained in the TiO2 mesoporous layers annealed at 500 °C for 30 min. Consequently, the best Jsc of 23.67 mA/cm2 was achieved in the IPSCs with TiO2 mesoporous layer annealed at 500 °C for 30 min. To verify the experimental results, the external quantum efficiency as a function of wavelength was also measured and shown in Fig. 9. It was found that the EQE changing tendency was quit fixed with the change of the Jsc. Moreover, to understand the changing 4
Organic Electronics 75 (2019) 105433
C.-T. Lee and S.-Y. Yang
Fig. 7. Dark current density-voltage characteristics of inverted perovskite solar cells without mesoporous structure and with various periodic TiO2 nanorod arrays.
Fig. 9. External quantum efficiency as a function of wavelength for the inverted perovskite solar cells without TiO2 nanorod array and with TiO2 mesoporous layers annealed at various temperatures for 30 min.
Fig. 8. Current density-voltage characteristics of inverted perovskite solar cells without TiO2 nanorod array and with TiO2 mesoporous layers annealed at various temperatures for 30 min.
Fig. 10. Dark current density-voltage characteristics of inverted perovskite solar cells without TiO2 nanorod array and with TiO2 mesoporous layers annealed at various temperatures for 30 min.
Table 3 Photovoltaic characteristics of inverted perovskite solar cells without TiO2 nanorod array and with TiO2 mesoporous layers annealed at various temperatures for 30 min. Annealing temperature (oC)
Jsc (mA/cm2)
Voc (V)
FF (%)
PCE (%)
400 450 500 550
22.74 23.14 23.67 23.06
0.75 0.76 0.77 0.76
67.31 68.63 69.85 68.75
11.51 12.10 12.73 12.09
Because the dark current density was a factor for determining Voc and FF of solar cells [22], the best results of Voc and FF were obtained in the IPSCs using TiO2 mesoporous layers annealed at 500 °C for 30 min. By trading off the parameters of Jsc, Voc, and FF, the best PCE of 12.73% was obtained. According to the above-mentioned experimented results of IPSCs, the optimal period of TiO2 nanorod array was 1.5 μm and the optimal annealing temperature of TiO2 film and TiO2 mesoporous layer was 500 °C for 30 min. By embedding the optimal TiO2 nanorod array and mesoporous layer, the J-V characteristics of the IPSCs shown in Fig. 1 were measured and illustrated in Fig. 11. In the IPSCs, the Jsc of 27.35 mA/cm2, Voc of 0.76 V, FF of 69.54%, and PCE of 14.47% were obtained. For the purpose of comparison, the J-V characteristics of the other structured IPSCs were also illustrated in Fig. 11. It was worth noting that the performances of IPSCs could be significantly improved by using the embedded TiO2 nanorod array and TiO2 mesoporous layer.
tendency of Voc and FF influenced by the annealing temperature as listed in Table 3, the dark current density of the IPSCs was measured and shown in Fig. 10. It was found that the dark current density decreased with an increase of annealing temperature until 500 °C and then increased by further increasing annealing temperature. The changing tendency of the dark current density was depended on the uniformity of porous distribution of the TiO2 mesoporous layers as shown in Fig. 4.
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Organic Electronics 75 (2019) 105433
C.-T. Lee and S.-Y. Yang
of the Republic of China under contract No. MOST 106-2923-E-155001-MY2 and MOST 105-2221-E-006-171-MY3. References [1] Y. Cai, S. Wang, M. Sun, X. Li, Y. Xiao, Mixed cations and mixed halide perovskite solar cell with lead thiocyanate additive for high efficiency and long-term moisture stability, Org. Electron. 53 (2018) 249–255. [2] E. Bagherzadeh-Khajehmarjan, A. Nikniazi, B. Olyaeefar, S. Ahmadi-Kandjani, J.M. Nunzi, Bulk luminescent solar concentrators based on organic-inorganic CH3NH3PbBr3 perovskite fluorophores, Sol. Energy Mater. Sol. Cells 192 (2019) 44–51. [3] G.S. Chen, Y.C. Chen, C.T. Lee, H.Y. Lee, Performance improvement of perovskite solar cells using electron and hole transport layers, Sol. Energy 174 (2018) 897–900. [4] C. Ren, Y. He, S. Li, Q. Sun, Y. Liu, Y. Wu, Y. Cui, Z. Li, H. Wang, Y. Hao, Y. Wu, Double electron transport layers for efficient and stable organic-inorganic hybrid perovskite solar cells, Org. Electron. 70 (2019) 292–299. [5] Q. Yang, K. Wang, H. Yu, X. Zhu, C. Han, L. Deng, H. Yang, F. Zhao, X. Sun, Q. Zhang, B. Hu, Surface polarization and recombination in organic-inorganic hybrid perovskite solar cells based on photo- and electrically induced negative capacitance studies, Org. Electron. 62 (2018) 203–208. [6] X. Zeng, T. Zhou, C. Leng, Z. Zang, M. Wang, W. Hu, X. Tang, S. Lu, L. Fang, M. Zhou, Performance improvement of perovskite solar cells by employing a CdSe quantum dot/PCBM composite as an electron transport layer, J. Mater. Chem. A 5 (2017) 17499–17505. [7] M. Wang, Z. Zang, B. Yang, X. Hu, K. Sun, L. Sun, Performance improvement of perovskite solar cells through enhanced holeextraction: the role of iodide concentration gradient, Sol. Energy Mater. Sol. Cells 185 (2018) 117–123. [8] T. Zhou, M. Wang, Z. Zang, L. Fang, Stable dynamics performance and high efficiency of ABX3-type super-alkali perovskites first obtained by introducing H5O2 cation, Adv. Energy Mater. 9 (2019) 1900664. [9] H.L. Huang, C.T. Lee, H.Y. Lee, Performance improvement mechanisms of P3HT:PCBM inverted polymer solar cells using extra PCBM and extra P3HT interfacial layers, Org. Electron. 21 (2015) 126–131. [10] G. Li, C.W. Chu, V. Shrotriya, J. Huang, Y. Yang, Efficient inverted polymer solar cells, Appl. Phys. Lett. 88 (2006) 253503. [11] H.Y. Lee, H.L. Huang, C.T. Lee, Performance enhancement of inverted polymer solar cells using roughened Al-doped ZnO nanorod array, Appl. Phys. Express 5 (2012) 122302. [12] C. Wang, X. Zhang, D. Cao, H. Yin, X. Li, P. Cheng, B. Mi, Z. Gao, W. Deng, In situ preparation of hierarchically structured dual-layer TiO2 films by E-spray method for efficient dye-sensitized solar cells, Org. Electron. 49 (2017) 135–141. [13] K. Qi, S.Y. Liu, Y. Chen, B. Xia, G.D. Li, A simple post-treatment with urea solution to enhance the photoelectric conversion efficiency for TiO2 dye-sensitized solar cells, Sol. Energy Mater. Sol. Cells 183 (2018) 193–199. [14] H. Guo, Z. Hu, L. Zhao, Y. Wu, S. Wang, B. Dong, L. Wan, J. Li, Facile synthesis of chrysanthemum flowers-like TiO2 hierarchical microstructures assembled by nanotube for high performance dye-sensitized solar cells, Org. Electron. 55 (2018) 97–105. [15] Y. Shi, L. Zhao, S. Wang, J. Li, B. Dong, Z. Xu, L. Wan, Double-layer composite film based on hollow TiO2 boxes and P25 as photoanode for enhanced efficiency in dyesensitized solar cells, Mater. Res. Bull. 59 (2014) 370–376. [16] C.T. Lee, H.Y. Juo, Multiple-submicron channel array gate-recessed AlGaN/GaN finMOSHEMTs, IEEE J. Electron Devices Soc. 6 (2018) 183–188. [17] N.J. Jeon, J.H. Noh, Y.C. Kim, W.S. Yang, S. Ryu, S.I. Seok, Solvent engineering for high-performance inorganic-organic hybrid perovskite solar cells, Nat. Mater. 13 (2014) 897–903. [18] X. Liu, Z. Wu, Y. Zhang, C. Tsamis, Low temperature Zn-doped TiO2 as electron transport layer for 19% efficient planar perovskite solar cells, Appl. Surf. Sci. 471 (2019) 28–35. [19] Z. Zhang, C. Shi, J. Chen, G. Xiao, L. Li, Combination of short-length TiO2 nanorod arrays and compact PbS quantum-dot thin films for efficient solid-state quantumdot-sensitized solar cells, Appl. Surf. Sci. 410 (2017) 8–13. [20] W.H. Nguyen, C.D. Bailie, E.L. Unger, M.D. McGehee, Enhancing the hole-conductivity of spiro-OMeTAD without oxygen or lithium salts by using spiro(TFSI)2 in perovskite and dye-sensitized solar cells, J. Am. Chem. Soc. 136 (2014) 10996–11001. [21] D. Zhao, T. Peng, L. Lu, P. Cai, P. Jiang, Z. Bian, Effect of annealing temperature on the photoelectrochemical properties of dye-sensitized solar cells made with mesoporous TiO2 nanoparticles, J. Phys. Chem. C 112 (2008) 8486–8494. [22] S.M. Sze, Physics of Semiconductor Devices, second ed., John Wiley and Sons Ltd, New York, 1981. [23] M. Landmann, E. Rauls, W.G. Schmidt, The electronic structure and optical response of rutile, anatase and brookite TiO2, J. Phys.-Condes. Matter 24 (2012) 195503.
Fig. 11. Current density-voltage characteristics of inverted perovskite solar cell without TiO2 nanorod array and TiO2 mesoporous layers, with TiO2 nanorod array only, with TiO2 mesoporous layer only, and with both TiO2 nanorod array and TiO2 mesoporous layer.
4. Conclusions In this study, to improve the performances of inverted perovskite solar cells, the TiO2 nanorod array and the TiO2 mesoporous layer were embedded on the TiO2 electron transport layer. To study the optimal period, various periodic TiO2 nanorod arrays were fabricated in IPSCs. Compared with the power conversion efficiency of 7.76% of the standard planar structure using TiO2 film as the electron transport layer only, the power conversion efficiency was improved to 11.96% in the IPSCs using TiO2 nanorod array with a period of 1.5 μm and a height of 150 nm. Since the crystallinity and the porous distribution of the TiO2 mesoporous layer were important issues for the performances of IPSCs, the 150-nm-thick TiO2 mesoporous layers were annealed for 30 min at various annealing temperatures. Due to the better crystallized anatase phase and more uniform porous distribution of the TiO2 mesoporous layer annealed at 500 °C for 30 min, the power conversion efficiency of 12.73% was obtained by using the TiO2 mesoporous layer. It was found that the power conversion efficiency was significantly improved compared with the power conversion efficiency of 7.66% of the IPSCs without TiO2 mesoporous layer. To further improve the performances of IPSCs, both the optimal 1.5-μm-periodic TiO2 nanorod array and the optimal 500 °C-annealed TiO2 mesoporous layer were embedded on the TiO2 electron transport layer, the power conversion efficiency of the resulting IPSCs was improved to 14.47%. It is well known that the performances of IPSCs are highly dependent on the structure and the quality of perovskite materials. In this study, since the structure of nanorod array and mesoporous layer are focused and emphasized, the general marked perovskite materials are used in the IPSCs. It is expected that the performances of the IPSCs can be more improved, if high quality perovskite materials are used. Acknowledgements This work was supported by the Ministry of Science and Technology
6
Contents lists available at ScienceDirect
Organic Electronics journal homepage: www.elsevier.com/locate/orgel
Performance improvement of inverted perovskite solar cells using TiO2 nanorod array and mesoporous structure
T
Ching-Ting Leea,b,c,∗, Sian-Yuan Yangb a
Department of Electrical Engineering, Yuan Ze University, Taoyuan, 320, Taiwan, ROC Institute of Microelectronics, Department of Electrical Engineering, National Cheng Kung University, Tainan, 701, Taiwan, ROC c Department of Photonics, National Cheng Kung University, Tainan, 701, Taiwan, ROC b
ARTICLE INFO
ABSTRACT
Keywords: Inverted perovskite solar cells Laser interference lithography system Mesoporous layer Nanorod array Titanium dioxide material
In view of the low carrier mobility of organic materials, the carrier collection ability was suffered from the short transport length before carriers were recombined. To improve performances by enhancing carrier collection ability, the optimal period was 1.5 μm which was obtained by changing the period of titanium dioxide (TiO2) nanorod array in the inverted perovskite solar cells (IPSCs). The power conversion efficiency was improved to 11.96% from the 7.66% of the standard planar IPSCs. Besides, due to the inherent properties of high absorption surface area and high light scattering ability, the 150-nm-thick TiO2 mesoporous layer was embedded in the TiO2 electron transport layer. By changing the annealing temperature, the optimal crystallinity of anatase phase and the optimal porous distribution were obtained in the TiO2 mesoporous layers annealed at 500 °C for 30 min. Using the optimal annealed TiO2 mesoporous layers in the IPSCs, the power conversion efficiency was improved to 12.73%. The power conversion efficiency of 14.47% was obtained for the IPSCs embedded with the optimal 1.5-μm-periodic TiO2 nanorod array and the optimal 500 °C-annealed TiO2 mesoporous layer in the electron transport layer, simultaneously.
1. Introduction Due to energy shortage and environment pollution, it is urgently needed to develop green renewable energy sources. Among the renewable energy sources, solar energy source has been substantially attracted and focused owing to its nonpollution and permanent sufficiency. In view of the inherent advantages of optical and electrical properties, the performances of organic-inorganic hybrid perovskite solar cells have been significantly improved, recently [1–8]. The perovskite solar cells become promising candidate of the organic solar cells. Because the inverted structure was designed and demonstrated to improve the performance of polymer solar cells [9,10], the inverted perovskite solar cells (IPSCs) were fabricated and studied in this work. To overcome the inherent disadvantage of short transport length of generated carriers caused by the low carrier mobility in the organic materials, the embedded nanorod array was proposed, previously [11]. Besides, owing to nontoxic, long-term durability, distinct photochemical activity, and stable chemical and physical properties, titanium dioxide (TiO2) was widely applied in dye-sensitized solar cells [12–15]. In this study, to improve performances of IPSCs, nanorod array and mesoporous structure were used to enhance carrier collection ability
∗
and to increase more exciton in active layer, respectively. The electron transport layer (ETL) of the IPSCs was constructed by TiO2 mesoporous layer/TiO2 nanorod array/TiO2 film. To study the optimal ETL structure, various annealed TiO2 mesoporous layers and various periodic TiO2 nanorod arrays were fabricated and studied. The current densityvoltage characteristics, external quantum efficiency (EQE) and dark current density of the resulting IPSCs were measured and analyzed. 2. Device fabrication experiments Fig. 1 shows the schematic configuration of the designed IPSCs. After cleaning the 200-nn-thick fluorine-doped tin oxide (FTO)-coated glass substrates using successive treatment under ultrasonic bath in acetone, methyl alcohol and deionized water, a 30-nm-thick TiO2 film was then deposited by an electron beam evaporator. The photoresist (AZ6112) was spread on the TiO2 film using a spin coater. Two-beam He-Cd laser interference photolithography system was used to perform interference grating strips [16]. After rotating an angle of 90°, the perpendicularly crossed grating patterns were defined by exposing the sample using the same process parameters. By changing the intersection angle of the two-beam He-Cd laser, various periodic photoresist
Corresponding author. Department of Electrical Engineering, Yuan Ze University, Taoyuan, 320, Taiwan, ROC. E-mail address: [email protected] (C.-T. Lee).
https://doi.org/10.1016/j.orgel.2019.105433 Received 17 June 2019; Received in revised form 8 August 2019; Accepted 24 August 2019 Available online 26 August 2019 1566-1199/ © 2019 Elsevier B.V. All rights reserved.
Organic Electronics 75 (2019) 105433
C.-T. Lee and S.-Y. Yang
Fig. 1. Schematic configuration of inverted perovskite solar cells.
patterns could be performed. After developing in developer solution for 45 s, various dimensional photoresist arrays were obtained. A 200-nmthick zinc oxide (ZnO) sacrificial film was deposited using a radio frequency magnetron sputtering system. After the photoresist array was lifted off using acetone, the perpendicularly crossed ZnO sacrificial grating structures were obtained. A 150-nm-thick TiO2 film was obliquely deposited using an electron beam evaporator. Various periodic TiO2 nanorod arrays were resulted, after the ZnO sacrificial grating structures were etched away by a chemical solution of H3PO4:H2O (2:100) at 90 °C. To form TiO2 mesoporous structure, the mixed solution of TiO2 powder (1 g), ethyl cellulose (5 g), terpineol anhydrous (0.2 mL), and ethanol (7.5 mL) was first prepared, and then the mixed solution was spread on the sample using a spin coater. To remove the residual organic materials, the sample was annealed at various temperatures. To deposit a 360-nm-thick perovskite active layer of IPSCs, the solution of methylammonium iodide (CH3NH3I, 0.40 g), lead iodide (PbI2, 1.16 g), γ-butyrolactone (GBL, 1 mL), and dimethyl sulfoxide (DMSO, 1 mL) was mixed and stirred at 70 °C for one day. By first rotating the spin coater at a speed of 1000 rpm for 10 s and then at 5000 rpm for 20 s, the mixed solution was spread on the sample. In the spreading process, a toluene was dropped on the sample at the middle spreading time to remove the uneasily volatile organic solvent [17]. Subsequently, the mixed solution of spiro-OMeTAD (80 mg), chlorobenzene solvent (1 mL), 4-tert-butylphyridine (TBP, 28.5 μL), and bis (trifluoromethane) sulfonamide lithium salt (Li-TFSI, 14.5 μL) was prepared and stirred for one day. The purpose of adding Li-TFSI was to improve the carrier mobility of spiro-OMeTAD hole transport layer (HTL) [18–20]. A 280-nm-thick spiro-OMeTAD HTL was deposited by dropping the mixed solution on the top surface of the perovskite active layer and spin-coating at 4000 rpm for 30 s. The sample was then baked at 90 °C for 5 min to remove the residual solvent. Finally, the device fabrication was completed by thermal evaporation of top silver electrode (100 nm) through shadow mask with a pressure of 4 × 10−4 Pa.
temperature until 500 °C. Based on the diffraction angle of 25.0°, the anatase phase of the annealed TiO2 crystallinity was deduced. Furthermore, the reduction of residual defects and the improvement of carrier mobility would be concluded from the enhanced peak intensity at a higher annealing temperature [21]. When the TiO2 films were annealed at 550 °C, its diffraction angle was changed to 28.0°. It was resulted that the crystallinity was changed from anatase phase to rutile phase. Using Hall measurement at a room temperature, electron concentration, electron mobility, and resistivity of the resulting TiO2 films were listed in Table 1. Due to the anatase phase and the highest peak intensity, the highest electron concentration of 8.2 × 1018 cm−3 and the highest electron mobility of 15.2 cm2/V-s were obtained in the TiO2 films annealed at 500 °C for 30 min. Besides, the crystalline properties of the TiO2 nanorods and the TiO2 mesoporous layer were assumed to be the similar crystallinity of the TiO2 film annealed at the same temperature. To observe the surface morphology, Fig. 4 (a), (b), (c), and (d) shows the scanning electron microscope images of the TiO2 mesoporous layers annealed for 30 min at 400, 450, 500, and 550 °C, respectively. It could be seen that more uniform porous distribution was formed in the TiO2 mesoporous layer annealed at 500 °C for 30 min. The current density-voltage (J-V) characteristics of IPSCs were measured at a room temperature using a J-V curve tracer under an illumination of 100 mW/cm2 with an AM 1.5G solar simulator. Fig. 5 shows the J-V characteristics of the IPSCs without mesoporous structure and with various periodic TiO2 nanorod arrays. Table 2 listed the photovoltaic characteristics of short-circuit current density (Jsc), opencircuit voltage (Voc), fill factor (FF), and power conversion efficiency (PCE). Fig. 6 shows the associated external quantum efficiency (EQE) as a function of wavelength in which was measured using a xenon lamp and a chopper with a lock-in amplifier for phase-sensitive detection. It was found that the EQE and Jsc of the IPSCs with TiO2 nanorod arrays was larger than that of those without TiO2 nanorod array. The improved performance was attributed to the increased carrier collection ability by the TiO2 nanorod array. Furthermore, the EQE and Jsc of the IPSCs increased by reducing the period of the TiO2 nanorod array. Those phenomena were attributed to the enhanced carrier collection ability, because the carrier transport length is short due to the low carrier mobility in organic materials. Therefore, before the carriers were recombined, more carriers could be collected by the cathode electrode and the anode electrode to improve EQE and Jsc in a narrower periodic TiO2 nanorod array. As listed in Table 2, Voc and FF of IPSCs decreased with a reduction of the period of TiO2 nanorod array. To study the mechanisms, the dark current density-voltage characteristics of the above-mentioned IPSCs were measured and shown in Fig. 7. It was seen that the dark current density increased with a decrease of the
3. Experimental results and discussion Fig. 2 (a), (b), and (c) shows the scanning electron microscope images of the TiO2 nanorod arrays with a period of 2.0, 1.5, and 1.0 μm, respectively. Fig. 2 (d) presents the profile of nanorod in the 2.0-μmperiodic TiO2 nanorod array measured using atomic force microscopy. It was found that the height of the TiO2 nanorod array was about 150 nm. To study the crystalline property, Fig. 3 shows the X-ray diffraction (XRD) spectra of the TiO2 films annealed at various temperatures for 30 min. It was observed that the peak intensity at the diffraction angle of 25.0° was enhanced with increasing the annealing 2
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Fig. 2. Scanning electron microscope images of TiO2 nanorod array with a period of (a) 2.0 μm, (b) 1.5 μm, and (c) 1.0 μm. (d) Atomic force microscope of 2.0 μm-periodic TiO2 nanorod array.
Fig. 3. X-ray diffraction spectra of TiO2 films annealed at various temperatures for 30 min. Table 1 Electrical properties of TiO2 films annealed at various temperatures for 30 min. Annealing temperature (oC)
Electron concentration (cm−3)
Electron mobility (cm2/V-s)
Resistivity (cm-Ω)
400 450 500 550
5.7 × 1018 6.2 × 1018 8.2 × 1018 6.2 × 1018
12.4 13.7 15.2 13.3
8.8 × 10−2 7.3 × 10−2 5.1 × 10−2 7.6 × 10−2
period of TiO2 nanorod array. Since the higher nanorod density could be obtained in a narrower periodic TiO2 nanorod array, the larger total surface area was resulted in a narrower periodic TiO2 nanorod array. The larger dark current density was contributed by the more defects resided on the larger total surface area of the tinier nanorods in a narrower periodic TiO2 nanorod array. Consequently, the Voc and FF were degraded by the existence of more defects and the larger dark current density [22]. Compared with the PCE of 7.66% of the IPSCs without TiO2 nanorod array, the PCE could be improved by using TiO2 nanorod array. By trading off the Jsc, Voc, and FF of the IPSCs, the best PCE of 11.96% was obtained by embedding 1.5 μm periodic TiO2 nanorod array. To study the optimal TiO2 mesoporous layer, the IPSCs without TiO2 nanorod array and with TiO2 mesoporous layers annealed at various temperatures for 30 min were fabricated and measured. The associated J-V characteristics and the photovoltaic characteristics were shown in Fig. 8 and were listed in Table 3, respectively. Compared with the photovoltaic characteristics without TiO2 mesoporous layer, the performances were significantly improved by using TiO2 mesoporous layer in the IPSCs. It was also found that the photovoltaic characteristics of the IPSCs were enhanced by increasing the annealing temperature until 500 °C and then decreased by further increasing annealing temperature to 550 °C. Compared with the rutile phase of the TiO2 layers annealed at 550 °C, the anatase phase of the TiO2 layers annealed at below 500 °C has better carrier mobility and conductivity as listed in Table 1 [23]. As the XRD spectra shown in Fig. 3, the crystallinity of the anatase phase of the TiO2 films was enhanced by increasing the annealing temperature to 500 °C. Besides, as the SEM images shown in Fig. 4, the more uniform 3
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Fig. 4. Scanning electron microscope images of TiO2 mesoporous layers annealed for 30 min at (a) 400 °C, (b) 450 °C, (c) 500 °C, and (d) 550 °C.
Fig. 5. Current density-voltage characteristics of inverted perovskite solar cells without mesoporous structure and with various periodic TiO2 nanorod arrays. Table 2 Photovoltaic characteristics of inverted perovskite solar cells without TiO2 mesoporous structure and with various periodic TiO2 nanorod arrays. Period (μm)
Jsc (mA/cm2)
Voc (V)
FF (%)
PCE (%)
without 3.0 2.5 2.0 1.5 1.0
15.73 19.35 21.81 23.79 25.28 26.05
0.74 0.74 0.74 0.73 0.73 0.72
65.80 65.67 65.49 65.27 65.01 63.70
7.66 9.40 10.52 11.38 11.96 11.88
Fig. 6. External quantum efficiency of inverted perovskite solar cells without mesoporous structure and with various periodic TiO2 nanorod arrays.
porous distribution was obtained in the TiO2 mesoporous layers annealed at 500 °C for 30 min. Consequently, the best Jsc of 23.67 mA/cm2 was achieved in the IPSCs with TiO2 mesoporous layer annealed at 500 °C for 30 min. To verify the experimental results, the external quantum efficiency as a function of wavelength was also measured and shown in Fig. 9. It was found that the EQE changing tendency was quit fixed with the change of the Jsc. Moreover, to understand the changing 4
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Fig. 7. Dark current density-voltage characteristics of inverted perovskite solar cells without mesoporous structure and with various periodic TiO2 nanorod arrays.
Fig. 9. External quantum efficiency as a function of wavelength for the inverted perovskite solar cells without TiO2 nanorod array and with TiO2 mesoporous layers annealed at various temperatures for 30 min.
Fig. 8. Current density-voltage characteristics of inverted perovskite solar cells without TiO2 nanorod array and with TiO2 mesoporous layers annealed at various temperatures for 30 min.
Fig. 10. Dark current density-voltage characteristics of inverted perovskite solar cells without TiO2 nanorod array and with TiO2 mesoporous layers annealed at various temperatures for 30 min.
Table 3 Photovoltaic characteristics of inverted perovskite solar cells without TiO2 nanorod array and with TiO2 mesoporous layers annealed at various temperatures for 30 min. Annealing temperature (oC)
Jsc (mA/cm2)
Voc (V)
FF (%)
PCE (%)
400 450 500 550
22.74 23.14 23.67 23.06
0.75 0.76 0.77 0.76
67.31 68.63 69.85 68.75
11.51 12.10 12.73 12.09
Because the dark current density was a factor for determining Voc and FF of solar cells [22], the best results of Voc and FF were obtained in the IPSCs using TiO2 mesoporous layers annealed at 500 °C for 30 min. By trading off the parameters of Jsc, Voc, and FF, the best PCE of 12.73% was obtained. According to the above-mentioned experimented results of IPSCs, the optimal period of TiO2 nanorod array was 1.5 μm and the optimal annealing temperature of TiO2 film and TiO2 mesoporous layer was 500 °C for 30 min. By embedding the optimal TiO2 nanorod array and mesoporous layer, the J-V characteristics of the IPSCs shown in Fig. 1 were measured and illustrated in Fig. 11. In the IPSCs, the Jsc of 27.35 mA/cm2, Voc of 0.76 V, FF of 69.54%, and PCE of 14.47% were obtained. For the purpose of comparison, the J-V characteristics of the other structured IPSCs were also illustrated in Fig. 11. It was worth noting that the performances of IPSCs could be significantly improved by using the embedded TiO2 nanorod array and TiO2 mesoporous layer.
tendency of Voc and FF influenced by the annealing temperature as listed in Table 3, the dark current density of the IPSCs was measured and shown in Fig. 10. It was found that the dark current density decreased with an increase of annealing temperature until 500 °C and then increased by further increasing annealing temperature. The changing tendency of the dark current density was depended on the uniformity of porous distribution of the TiO2 mesoporous layers as shown in Fig. 4.
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of the Republic of China under contract No. MOST 106-2923-E-155001-MY2 and MOST 105-2221-E-006-171-MY3. References [1] Y. Cai, S. Wang, M. Sun, X. Li, Y. Xiao, Mixed cations and mixed halide perovskite solar cell with lead thiocyanate additive for high efficiency and long-term moisture stability, Org. Electron. 53 (2018) 249–255. [2] E. Bagherzadeh-Khajehmarjan, A. Nikniazi, B. Olyaeefar, S. Ahmadi-Kandjani, J.M. Nunzi, Bulk luminescent solar concentrators based on organic-inorganic CH3NH3PbBr3 perovskite fluorophores, Sol. Energy Mater. Sol. Cells 192 (2019) 44–51. [3] G.S. Chen, Y.C. Chen, C.T. Lee, H.Y. Lee, Performance improvement of perovskite solar cells using electron and hole transport layers, Sol. Energy 174 (2018) 897–900. [4] C. Ren, Y. He, S. Li, Q. Sun, Y. Liu, Y. Wu, Y. Cui, Z. Li, H. Wang, Y. Hao, Y. Wu, Double electron transport layers for efficient and stable organic-inorganic hybrid perovskite solar cells, Org. Electron. 70 (2019) 292–299. [5] Q. Yang, K. Wang, H. Yu, X. Zhu, C. Han, L. Deng, H. Yang, F. Zhao, X. Sun, Q. Zhang, B. Hu, Surface polarization and recombination in organic-inorganic hybrid perovskite solar cells based on photo- and electrically induced negative capacitance studies, Org. Electron. 62 (2018) 203–208. [6] X. Zeng, T. Zhou, C. Leng, Z. Zang, M. Wang, W. Hu, X. Tang, S. Lu, L. Fang, M. Zhou, Performance improvement of perovskite solar cells by employing a CdSe quantum dot/PCBM composite as an electron transport layer, J. Mater. Chem. A 5 (2017) 17499–17505. [7] M. Wang, Z. Zang, B. Yang, X. Hu, K. Sun, L. Sun, Performance improvement of perovskite solar cells through enhanced holeextraction: the role of iodide concentration gradient, Sol. Energy Mater. Sol. Cells 185 (2018) 117–123. [8] T. Zhou, M. Wang, Z. Zang, L. Fang, Stable dynamics performance and high efficiency of ABX3-type super-alkali perovskites first obtained by introducing H5O2 cation, Adv. Energy Mater. 9 (2019) 1900664. [9] H.L. Huang, C.T. Lee, H.Y. Lee, Performance improvement mechanisms of P3HT:PCBM inverted polymer solar cells using extra PCBM and extra P3HT interfacial layers, Org. Electron. 21 (2015) 126–131. [10] G. Li, C.W. Chu, V. Shrotriya, J. Huang, Y. Yang, Efficient inverted polymer solar cells, Appl. Phys. Lett. 88 (2006) 253503. [11] H.Y. Lee, H.L. Huang, C.T. Lee, Performance enhancement of inverted polymer solar cells using roughened Al-doped ZnO nanorod array, Appl. Phys. Express 5 (2012) 122302. [12] C. Wang, X. Zhang, D. Cao, H. Yin, X. Li, P. Cheng, B. Mi, Z. Gao, W. Deng, In situ preparation of hierarchically structured dual-layer TiO2 films by E-spray method for efficient dye-sensitized solar cells, Org. Electron. 49 (2017) 135–141. [13] K. Qi, S.Y. Liu, Y. Chen, B. Xia, G.D. Li, A simple post-treatment with urea solution to enhance the photoelectric conversion efficiency for TiO2 dye-sensitized solar cells, Sol. Energy Mater. Sol. Cells 183 (2018) 193–199. [14] H. Guo, Z. Hu, L. Zhao, Y. Wu, S. Wang, B. Dong, L. Wan, J. Li, Facile synthesis of chrysanthemum flowers-like TiO2 hierarchical microstructures assembled by nanotube for high performance dye-sensitized solar cells, Org. Electron. 55 (2018) 97–105. [15] Y. Shi, L. Zhao, S. Wang, J. Li, B. Dong, Z. Xu, L. Wan, Double-layer composite film based on hollow TiO2 boxes and P25 as photoanode for enhanced efficiency in dyesensitized solar cells, Mater. Res. Bull. 59 (2014) 370–376. [16] C.T. Lee, H.Y. Juo, Multiple-submicron channel array gate-recessed AlGaN/GaN finMOSHEMTs, IEEE J. Electron Devices Soc. 6 (2018) 183–188. [17] N.J. Jeon, J.H. Noh, Y.C. Kim, W.S. Yang, S. Ryu, S.I. Seok, Solvent engineering for high-performance inorganic-organic hybrid perovskite solar cells, Nat. Mater. 13 (2014) 897–903. [18] X. Liu, Z. Wu, Y. Zhang, C. Tsamis, Low temperature Zn-doped TiO2 as electron transport layer for 19% efficient planar perovskite solar cells, Appl. Surf. Sci. 471 (2019) 28–35. [19] Z. Zhang, C. Shi, J. Chen, G. Xiao, L. Li, Combination of short-length TiO2 nanorod arrays and compact PbS quantum-dot thin films for efficient solid-state quantumdot-sensitized solar cells, Appl. Surf. Sci. 410 (2017) 8–13. [20] W.H. Nguyen, C.D. Bailie, E.L. Unger, M.D. McGehee, Enhancing the hole-conductivity of spiro-OMeTAD without oxygen or lithium salts by using spiro(TFSI)2 in perovskite and dye-sensitized solar cells, J. Am. Chem. Soc. 136 (2014) 10996–11001. [21] D. Zhao, T. Peng, L. Lu, P. Cai, P. Jiang, Z. Bian, Effect of annealing temperature on the photoelectrochemical properties of dye-sensitized solar cells made with mesoporous TiO2 nanoparticles, J. Phys. Chem. C 112 (2008) 8486–8494. [22] S.M. Sze, Physics of Semiconductor Devices, second ed., John Wiley and Sons Ltd, New York, 1981. [23] M. Landmann, E. Rauls, W.G. Schmidt, The electronic structure and optical response of rutile, anatase and brookite TiO2, J. Phys.-Condes. Matter 24 (2012) 195503.
Fig. 11. Current density-voltage characteristics of inverted perovskite solar cell without TiO2 nanorod array and TiO2 mesoporous layers, with TiO2 nanorod array only, with TiO2 mesoporous layer only, and with both TiO2 nanorod array and TiO2 mesoporous layer.
4. Conclusions In this study, to improve the performances of inverted perovskite solar cells, the TiO2 nanorod array and the TiO2 mesoporous layer were embedded on the TiO2 electron transport layer. To study the optimal period, various periodic TiO2 nanorod arrays were fabricated in IPSCs. Compared with the power conversion efficiency of 7.76% of the standard planar structure using TiO2 film as the electron transport layer only, the power conversion efficiency was improved to 11.96% in the IPSCs using TiO2 nanorod array with a period of 1.5 μm and a height of 150 nm. Since the crystallinity and the porous distribution of the TiO2 mesoporous layer were important issues for the performances of IPSCs, the 150-nm-thick TiO2 mesoporous layers were annealed for 30 min at various annealing temperatures. Due to the better crystallized anatase phase and more uniform porous distribution of the TiO2 mesoporous layer annealed at 500 °C for 30 min, the power conversion efficiency of 12.73% was obtained by using the TiO2 mesoporous layer. It was found that the power conversion efficiency was significantly improved compared with the power conversion efficiency of 7.66% of the IPSCs without TiO2 mesoporous layer. To further improve the performances of IPSCs, both the optimal 1.5-μm-periodic TiO2 nanorod array and the optimal 500 °C-annealed TiO2 mesoporous layer were embedded on the TiO2 electron transport layer, the power conversion efficiency of the resulting IPSCs was improved to 14.47%. It is well known that the performances of IPSCs are highly dependent on the structure and the quality of perovskite materials. In this study, since the structure of nanorod array and mesoporous layer are focused and emphasized, the general marked perovskite materials are used in the IPSCs. It is expected that the performances of the IPSCs can be more improved, if high quality perovskite materials are used. Acknowledgements This work was supported by the Ministry of Science and Technology
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