Bernhardt Annik, Ambagaspitiya Tharushi D, Kordesch Martin E, Cimatu Katherine Leslee A, Chen Jixin
Department of Chemistry and Biochemistry, Ohio University, Athens, OH 45701, United States.
Department of Chemistry, University of Leipzig, 04103, Leipzig, Germany.
Chemphyschem. 2022 Aug 3;23(15):e202200022. doi: 10.1002/cphc.202200022. Epub 2022 Jun 7.
Methylammonium lead iodide bromides MAPb(Br I ) are a class of mixed halide lead perovskites, materials that offer high-power conversion efficiencies and bandgap tunability. For these reasons, they are a promising absorber material for future solar cells, although their use is still limited due to several factors. The reversible phase segregation under even low light intensities is one of them, lowering the effective bandgap due to local segregation into iodide-rich and bromide-rich phases. While several studies have been done to illuminate the mechanism and suppression of phase segregation, challenges remain to understand its kinetics. We obtained dynamic ellipsometric measurements from x=0.5 mixed halide lead perovskite thin films protected by a polystyrene layer under green laser light with a power density of ∼11 W/cm . Time constants between 1.7(±0.7)×10 s for the segregation and 1.5(±0.6)×10 s for recovery were calculated. The phase segregation rate constants are surprisingly two orders of magnitude slower than and the recovery rate is consistent with those measured using photoluminescence methods under similar conditions. These results confirm a concern in the literature about the complexity in the phase separation kinetics measured from photoluminescence. We expect ellipsometry to serve as a complementary technique to other spectroscopies in studying mixed-halide lead perovskites phase segregation in the future.
甲基碘化溴化铅（MAPb(BrI)）是一类混合卤化物铅基钙钛矿材料，具有高功率转换效率和带隙可调性。基于这些原因，它们是未来太阳能电池中很有前景的吸收材料，尽管由于多种因素其应用仍然有限。即使在低光照强度下的可逆相分离就是其中一个因素，它会由于局部偏析成富碘相和富溴相而降低有效带隙。虽然已经开展了多项研究来阐明相分离的机制及抑制方法，但在理解其动力学方面仍存在挑战。我们对由聚苯乙烯层保护的x = 0.5混合卤化物铅基钙钛矿薄膜在功率密度约为11W/cm的绿色激光下进行了动态椭偏测量。计算出相分离的时间常数为1.7(±0.7)×10 s，恢复的时间常数为1.5(±0.6)×10 s。相分离速率常数比在类似条件下使用光致发光方法测得的结果慢两个数量级，而恢复速率与之相符。这些结果证实了文献中关于从光致发光测量相分离动力学的复杂性的担忧。我们预计椭偏测量法在未来研究混合卤化物铅基钙钛矿相分离时可作为其他光谱学的补充技术。
