Bischak Connor G, Wong Andrew B, Lin Elbert, Limmer David T, Yang Peidong, Ginsberg Naomi S
Department of Chemistry , University of California , Berkeley , California 94720 , United States.
Kavli Energy NanoScience Institute , Berkeley , California 94720 , United States.
J Phys Chem Lett. 2018 Jul 19;9(14):3998-4005. doi: 10.1021/acs.jpclett.8b01512. Epub 2018 Jul 6.
Photoinduced phase separation in mixed halide perovskites emerges from their electro-mechanical properties and high ionic conductivities, resulting in photoinduced I-rich charge carrier traps that diminish photovoltaic performance. Whether photoinduced phase separation stems from the polycrystalline microstructure or is an intrinsic material property has been an open question. We investigate the nanoscale photoinduced behavior of single-crystal mixed Br/I methylammonium (MA) lead halide perovskite (MAPb(Br I)) nanoplates, eliminating effects from extended structural defects. Even in these nanoplates, we find that phase separation occurs, resulting in I-rich clusters that are nucleated stochastically and stabilized by polarons. Upon lowering the electron-phonon coupling strength by partially exchanging MA for Cs, a phase-separated steady state is not reached, nevertheless transient I clustering still occurs. Our results, supported by multiscale modeling, demonstrate that photoinduced phase separation is an intrinsic property of mixed halide perovskites, the extent and dynamics of which depends on the electron-phonon coupling strength.
混合卤化物钙钛矿中的光致相分离源于其机电性能和高离子电导率，导致富碘的光生电荷载流子陷阱，从而降低光伏性能。光致相分离是源于多晶微观结构还是材料的固有特性，一直是个悬而未决的问题。我们研究了单晶混合溴/碘甲基铵（MA）铅卤化物钙钛矿（MAPb(Br I)）纳米板的纳米级光致行为，消除了扩展结构缺陷的影响。即使在这些纳米板中，我们也发现会发生相分离，形成随机成核并由极化子稳定的富碘团簇。通过用铯部分取代甲基铵来降低电子-声子耦合强度时，虽然未达到相分离稳态，但仍会发生瞬态碘团簇化。我们的结果得到多尺度建模的支持，表明光致相分离是混合卤化物钙钛矿的固有特性，其程度和动力学取决于电子-声子耦合强度。
