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Ruddlesden-Popper Perovskite Solar Cells
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Ruddlesden-Popper Perovskite Solar Cells Teck Ming Koh,1 Benny Febriansyah,2,3 and Nripan Mathews1,4,* Ruddlesden-Popper halide perovskites are now viewed as a promising avenue in perovskite solar cells in terms of both stability and high power-conversion efficiencies. We provide context to the efforts of Kanatzidis and coworkers, who, in this issue of Chem, have unveiled promising developments in the higher members of the (CH3(CH2)3NH3)2(CH3NH3)n 1PbnI3n+1 series.
Since the first reports of stable solid-state organic-inorganic perovskites, intense research focus has centered on these materials and their variants. Solution-processed perovskite solar cells (PSCs) can now match the efficiency (22%) of inorganic thin-film technologies, justifying the research focus. Attention has now turned to improving the stability of PSCs. The PSCs that have been developed are unstable, especially over the long term under ambient conditions. The hydrophilicity and volatility of methylammonium cations (MA+) make the archetypical organic lead iodide perovskite (MAPbI3) vulnerable to degradation through humidity and heat. More complex multilayered structures in perovskites can be conceived by the insertion of alternating larger organic molecules between the adjacent PbI64 inorganic sheets. Tuning the organic cations and altering the ratio of the perovskite constituents can yield RuddlesdenPopper perovskites (An 1A’2MnX3n+1) with controlled inorganic layer stacking (n). These allow a wider compositional flexibility and represent a great avenue for obtaining ambient stable perovskite materials. The formation of such layered structures has led to perovskites with tunable photophysical and electronic properties. A few prototypical examples of RuddlesdenPopper perovskites include (CH3(CH2)3 NH3)2(CH3NH3)2Pb3I10 and (CH3(CH2)3
326
NH3)2(CH3NH3)3Pb4I13, which crystallize into well-organized layered structures.1 Properties such as the band gap, band energy levels, carrier binding energy, and internal charge transport can be intentionally tuned by alterations in the types of organic cations, the thickness of the inorganic slabs, and the fabrication processes (spin coating, hot casting, and dipping).2–4 The first demonstration of RuddlesdenPopper perovskites in PSCs was reported in 2014 by Smith et al.,2 who examined (PEA)2(MA)2[Pb3I10] (PEA+ = phenethylammonium). Despite the reduced efficiencies, this Ruddlesden-Popper perovskite showed high moisture resistance under storage for 46 days in 52% relative humidity. In 2016, Tsai et al. achieved a breakthrough in the power-conversion efficiencies of Ruddlesden-Popper perovskite photovoltaics by producing Ruddlesden-Popper layered perovskites (BA)2(MA)3Pb4I13 (BA+ = butylammonium) with an out-of-plane orientation in which charge transport occurred predominantly without inhibition through the PbI64 inorganic slabs.3 This multilayered perovskite was fabricated by a hot-casting technique, which generated thin films with near single-crystalline quality. The efficiency of these RuddlesdenPopper photovoltaics was recorded to be as high as 12.52% with a stability > 2,000 hr under illumination and 65% humidity.
Chem 2, 326–333, March 9, 2017 ª 2017 Elsevier Inc.
In this issue of Chem, Kanatzidis and coworkers have isolated the single crystal of phase-pure Ruddlesden-Popper layered perovskites (BA)2(MA)4Pb5I16 and performed detailed photophysical characterization.5 This RuddlesdenPopper perovskite crystal exhibits a strong vertical growth tendency, such that some platelets grow perpendicularly to the existing (010) plane, leading to extensive twin intergrowth. In contrast to the bulk MAPbI3, which had degraded, the Ruddlesden-Popper perovskite crystal demonstrated ambient stability in humid air of up to 5 months. Most interestingly, the authors revealed the existence of a disproportionation reaction from (BA)2(MA)4Pb5I16 (n = 5) into (BA)2(MA)2Pb3I10 (n = 3) and MAPbI3$H2O. The disproportionation mechanism has been proposed as a possible mechanism for improving the stability of the overall material because whereas the MAPbI3$H2O species get secluded upon degradation, the moisture-resistant n = 3 compound would act as a ‘‘skin’’ ensheathing the remaining n = 5 material in the inner core. The lower band gap and excitonic binding energy are believed to play a crucial role in the enhancement of light harvesting and photogenerated charge-carrier collection, both of which are important parameters in maximizing solar cell efficiency. Ruddlesden-Popper perovskites have become promising candidates for
1Energy
Research Institute, Nanyang Technological University, Research Techno Plaza, X-Frontier Block Level 5, 50 Nanyang Avenue, Singapore 637553, Singapore
2Interdisciplinary
Graduate School, Energy Research Institute, Nanyang Technological University, Singapore 639798, Singapore
3Division
of Chemistry and Biological Chemistry, School of Physical and Mathematical Sciences, Nanyang Technological University, 21 Nanyang Link, Singapore 637371, Singapore
4School
of Materials Science and Engineering, Nanyang Technological University, 50 Nanyang Avenue, Singapore 639798, Singapore *Correspondence: [email protected] http://dx.doi.org/10.1016/j.chempr.2017.02.015
overcoming the stability challenges in 3D perovskites because they can incorporate more hydrophobic organic cations while potentially avoiding the pitfalls of poor charge transport.6,7 Band gaps, carrier binding energy, and charge-transport properties can be rationally tuned in Ruddlesden-Popper perovskites by modulation of the stoichiometric ratio of the perovskite components, the choice of proper deposition techniques, and rational selection of the organic cations. It has to be noted that multilayered perovskite formation in single crystals and thin films (from spin coating or hot
casting) could be different as a result of the distinct crystallization rates. Thus, thin-film formation of phasepure Ruddlesden-Popper perovskites needs to be carefully controlled. We foresee that tremendous research efforts will be invested in RuddlesdenPopper perovskites for the development of high-efficiency PSCs with long-term stability. 1. Cao, D.H., Stoumpos, C.C., Farha, O.K., Hupp, J.T., and Kanatzidis, M.G. (2015). J. Am. Chem. Soc. 137, 7843–7850. 2. Smith, I.C., Hoke, E.T., Solis-Ibarra, D., McGehee, M.D., and Karunadasa, H.I. (2014). Angew. Chem. Int. Ed. 53, 11232–11235.
3. Tsai, H., Nie, W., Blancon, J.C., Stoumpos, C.C., Asadpour, R., Harutyunyan, B., Neukirch, A.J., Verduzco, R., Crochet, J.J., Tretiak, S., et al. (2016). Nature 536, 312–316. 4. Koh, T.M., Shanmugam, V., Schlipf, J., Oesinghaus, L., Mu¨ller-Buschbaum, P., Ramakrishnan, N., Swamy, V., Mathews, N., Boix, P.P., and Mhaisalkar, S.G. (2016). Adv. Mater. 28, 3653–3661. 5. Stoumpos, C.C., Soe, C.M.M., Tsai, H., Nie, W., Blancon, J.-C., Cao, D.H., Liu, F., Traore´, B., Katan, C., Even, J., et al. (2017). Chem 2, this issue, 427–440. 6. Boix, P.P., Agarwala, S., Koh, T.M., Mathews, N., and Mhaisalkar, S.G. (2015). J. Phys. Chem. Lett. 6, 898–907. 7. Koh, T.M., Thirumal, K., Soo, H.S., and Mathews, N. (2016). ChemSusChem 9, 2541–2558.
Preview parameter (Hansch parameter: pR = 1.04),2 and specific electronic properties3 and induces specific structural features.4 Such an interest in this substituent is well illustrated with riluzole (Rilutek), the only currently approved drug for amyotrophic lateral sclerosis (Lou Gehrig’s disease or Charcot’s disease).5
New Reagents for Asymmetric Trifluoromethoxylation Fabien Toulgoat1,2 and Thierry Billard1,3,* Trifluoromethoxylation reactions are still limited, and new strategies are greatly required in light of the growing interest in CF3O molecules. In a recent publication in Nature Chemistry, Tang and co-workers used new reagents, easily accessible and simple to handle, to perform asymmetric bromotrifluoromethoxylation of alkenes. Besides the development of new reagents, this work is the first example of asymmetric trifluoromethoxylation.
With the fluorine discovery by Moissan in 1886, the use of fluorinated compounds has continued to increase in a large panel of applications, mainly because of the extraordinary characteristics of the fluorine atom, which confers molecule-specific, and often unusual, properties.1 Among all the fluorinated groups envisaged to adorn organic substrates, the association between the CF3 group and heteroatoms occupies a special place. Indeed, CF3chalcogen combinations lead to new substituents with interesting electronic
and physicochemical properties that bring pertinent modifications to molecules bearing such groups,1 particularly the increased lipophilicity of compounds that favor their bioavailability, an important parameter for life science applications.1 Compared with other chalcogens associations, the trifluoromethoxy group is highly valued because of its distinctive properties. More specifically, this group presents high chemical and metabolic stability, an interesting lipophilicity
However, despite this fascinating interest in trifluoromethoxylated molecules, their syntheses are still limited.6 In particular, direct trifluoromethoxylation remains underdeveloped. This could be explained by the instability of the trifluoromethoxide anion, which collapses rapidly to difluorophosgene and a fluoride anion. Consequently, this chemistry requires a reagent able to generate the CF3O anion.
1ICBMS
UMR 5246 CNRS, Institute of Chemistry and Biochemistry, Universite´ Lyon 1, Centre National de la Recherche Scientifique, 69622 Villeurbanne, France 2E ´ cole Supe´rieure de Chimie Physique E´lectronique de Lyon, 69616 Villeurbanne, France 3CERMEP
– In Vivo Imaging, Groupement Hospitalier Est, 69003 Lyon, France *Correspondence: [email protected] http://dx.doi.org/10.1016/j.chempr.2017.02.008
Chem 2, 326–333, March 9, 2017 ª 2017 Elsevier Inc.
327
Ruddlesden-Popper Perovskite Solar Cells Teck Ming Koh,1 Benny Febriansyah,2,3 and Nripan Mathews1,4,* Ruddlesden-Popper halide perovskites are now viewed as a promising avenue in perovskite solar cells in terms of both stability and high power-conversion efficiencies. We provide context to the efforts of Kanatzidis and coworkers, who, in this issue of Chem, have unveiled promising developments in the higher members of the (CH3(CH2)3NH3)2(CH3NH3)n 1PbnI3n+1 series.
Since the first reports of stable solid-state organic-inorganic perovskites, intense research focus has centered on these materials and their variants. Solution-processed perovskite solar cells (PSCs) can now match the efficiency (22%) of inorganic thin-film technologies, justifying the research focus. Attention has now turned to improving the stability of PSCs. The PSCs that have been developed are unstable, especially over the long term under ambient conditions. The hydrophilicity and volatility of methylammonium cations (MA+) make the archetypical organic lead iodide perovskite (MAPbI3) vulnerable to degradation through humidity and heat. More complex multilayered structures in perovskites can be conceived by the insertion of alternating larger organic molecules between the adjacent PbI64 inorganic sheets. Tuning the organic cations and altering the ratio of the perovskite constituents can yield RuddlesdenPopper perovskites (An 1A’2MnX3n+1) with controlled inorganic layer stacking (n). These allow a wider compositional flexibility and represent a great avenue for obtaining ambient stable perovskite materials. The formation of such layered structures has led to perovskites with tunable photophysical and electronic properties. A few prototypical examples of RuddlesdenPopper perovskites include (CH3(CH2)3 NH3)2(CH3NH3)2Pb3I10 and (CH3(CH2)3
326
NH3)2(CH3NH3)3Pb4I13, which crystallize into well-organized layered structures.1 Properties such as the band gap, band energy levels, carrier binding energy, and internal charge transport can be intentionally tuned by alterations in the types of organic cations, the thickness of the inorganic slabs, and the fabrication processes (spin coating, hot casting, and dipping).2–4 The first demonstration of RuddlesdenPopper perovskites in PSCs was reported in 2014 by Smith et al.,2 who examined (PEA)2(MA)2[Pb3I10] (PEA+ = phenethylammonium). Despite the reduced efficiencies, this Ruddlesden-Popper perovskite showed high moisture resistance under storage for 46 days in 52% relative humidity. In 2016, Tsai et al. achieved a breakthrough in the power-conversion efficiencies of Ruddlesden-Popper perovskite photovoltaics by producing Ruddlesden-Popper layered perovskites (BA)2(MA)3Pb4I13 (BA+ = butylammonium) with an out-of-plane orientation in which charge transport occurred predominantly without inhibition through the PbI64 inorganic slabs.3 This multilayered perovskite was fabricated by a hot-casting technique, which generated thin films with near single-crystalline quality. The efficiency of these RuddlesdenPopper photovoltaics was recorded to be as high as 12.52% with a stability > 2,000 hr under illumination and 65% humidity.
Chem 2, 326–333, March 9, 2017 ª 2017 Elsevier Inc.
In this issue of Chem, Kanatzidis and coworkers have isolated the single crystal of phase-pure Ruddlesden-Popper layered perovskites (BA)2(MA)4Pb5I16 and performed detailed photophysical characterization.5 This RuddlesdenPopper perovskite crystal exhibits a strong vertical growth tendency, such that some platelets grow perpendicularly to the existing (010) plane, leading to extensive twin intergrowth. In contrast to the bulk MAPbI3, which had degraded, the Ruddlesden-Popper perovskite crystal demonstrated ambient stability in humid air of up to 5 months. Most interestingly, the authors revealed the existence of a disproportionation reaction from (BA)2(MA)4Pb5I16 (n = 5) into (BA)2(MA)2Pb3I10 (n = 3) and MAPbI3$H2O. The disproportionation mechanism has been proposed as a possible mechanism for improving the stability of the overall material because whereas the MAPbI3$H2O species get secluded upon degradation, the moisture-resistant n = 3 compound would act as a ‘‘skin’’ ensheathing the remaining n = 5 material in the inner core. The lower band gap and excitonic binding energy are believed to play a crucial role in the enhancement of light harvesting and photogenerated charge-carrier collection, both of which are important parameters in maximizing solar cell efficiency. Ruddlesden-Popper perovskites have become promising candidates for
1Energy
Research Institute, Nanyang Technological University, Research Techno Plaza, X-Frontier Block Level 5, 50 Nanyang Avenue, Singapore 637553, Singapore
2Interdisciplinary
Graduate School, Energy Research Institute, Nanyang Technological University, Singapore 639798, Singapore
3Division
of Chemistry and Biological Chemistry, School of Physical and Mathematical Sciences, Nanyang Technological University, 21 Nanyang Link, Singapore 637371, Singapore
4School
of Materials Science and Engineering, Nanyang Technological University, 50 Nanyang Avenue, Singapore 639798, Singapore *Correspondence: [email protected] http://dx.doi.org/10.1016/j.chempr.2017.02.015
overcoming the stability challenges in 3D perovskites because they can incorporate more hydrophobic organic cations while potentially avoiding the pitfalls of poor charge transport.6,7 Band gaps, carrier binding energy, and charge-transport properties can be rationally tuned in Ruddlesden-Popper perovskites by modulation of the stoichiometric ratio of the perovskite components, the choice of proper deposition techniques, and rational selection of the organic cations. It has to be noted that multilayered perovskite formation in single crystals and thin films (from spin coating or hot
casting) could be different as a result of the distinct crystallization rates. Thus, thin-film formation of phasepure Ruddlesden-Popper perovskites needs to be carefully controlled. We foresee that tremendous research efforts will be invested in RuddlesdenPopper perovskites for the development of high-efficiency PSCs with long-term stability. 1. Cao, D.H., Stoumpos, C.C., Farha, O.K., Hupp, J.T., and Kanatzidis, M.G. (2015). J. Am. Chem. Soc. 137, 7843–7850. 2. Smith, I.C., Hoke, E.T., Solis-Ibarra, D., McGehee, M.D., and Karunadasa, H.I. (2014). Angew. Chem. Int. Ed. 53, 11232–11235.
3. Tsai, H., Nie, W., Blancon, J.C., Stoumpos, C.C., Asadpour, R., Harutyunyan, B., Neukirch, A.J., Verduzco, R., Crochet, J.J., Tretiak, S., et al. (2016). Nature 536, 312–316. 4. Koh, T.M., Shanmugam, V., Schlipf, J., Oesinghaus, L., Mu¨ller-Buschbaum, P., Ramakrishnan, N., Swamy, V., Mathews, N., Boix, P.P., and Mhaisalkar, S.G. (2016). Adv. Mater. 28, 3653–3661. 5. Stoumpos, C.C., Soe, C.M.M., Tsai, H., Nie, W., Blancon, J.-C., Cao, D.H., Liu, F., Traore´, B., Katan, C., Even, J., et al. (2017). Chem 2, this issue, 427–440. 6. Boix, P.P., Agarwala, S., Koh, T.M., Mathews, N., and Mhaisalkar, S.G. (2015). J. Phys. Chem. Lett. 6, 898–907. 7. Koh, T.M., Thirumal, K., Soo, H.S., and Mathews, N. (2016). ChemSusChem 9, 2541–2558.
Preview parameter (Hansch parameter: pR = 1.04),2 and specific electronic properties3 and induces specific structural features.4 Such an interest in this substituent is well illustrated with riluzole (Rilutek), the only currently approved drug for amyotrophic lateral sclerosis (Lou Gehrig’s disease or Charcot’s disease).5
New Reagents for Asymmetric Trifluoromethoxylation Fabien Toulgoat1,2 and Thierry Billard1,3,* Trifluoromethoxylation reactions are still limited, and new strategies are greatly required in light of the growing interest in CF3O molecules. In a recent publication in Nature Chemistry, Tang and co-workers used new reagents, easily accessible and simple to handle, to perform asymmetric bromotrifluoromethoxylation of alkenes. Besides the development of new reagents, this work is the first example of asymmetric trifluoromethoxylation.
With the fluorine discovery by Moissan in 1886, the use of fluorinated compounds has continued to increase in a large panel of applications, mainly because of the extraordinary characteristics of the fluorine atom, which confers molecule-specific, and often unusual, properties.1 Among all the fluorinated groups envisaged to adorn organic substrates, the association between the CF3 group and heteroatoms occupies a special place. Indeed, CF3chalcogen combinations lead to new substituents with interesting electronic
and physicochemical properties that bring pertinent modifications to molecules bearing such groups,1 particularly the increased lipophilicity of compounds that favor their bioavailability, an important parameter for life science applications.1 Compared with other chalcogens associations, the trifluoromethoxy group is highly valued because of its distinctive properties. More specifically, this group presents high chemical and metabolic stability, an interesting lipophilicity
However, despite this fascinating interest in trifluoromethoxylated molecules, their syntheses are still limited.6 In particular, direct trifluoromethoxylation remains underdeveloped. This could be explained by the instability of the trifluoromethoxide anion, which collapses rapidly to difluorophosgene and a fluoride anion. Consequently, this chemistry requires a reagent able to generate the CF3O anion.
1ICBMS
UMR 5246 CNRS, Institute of Chemistry and Biochemistry, Universite´ Lyon 1, Centre National de la Recherche Scientifique, 69622 Villeurbanne, France 2E ´ cole Supe´rieure de Chimie Physique E´lectronique de Lyon, 69616 Villeurbanne, France 3CERMEP
– In Vivo Imaging, Groupement Hospitalier Est, 69003 Lyon, France *Correspondence: [email protected] http://dx.doi.org/10.1016/j.chempr.2017.02.008
Chem 2, 326–333, March 9, 2017 ª 2017 Elsevier Inc.
327