Shaun Tan1,Tianyi Huang1,Qiyu Xing1,Yang Yang1
University of California, Los Angeles1
Shaun Tan1,Tianyi Huang1,Qiyu Xing1,Yang Yang1
University of California, Los Angeles1
Residual PbI<sub>2</sub> in the halide perovskite thin film is known to beneficially increase the performance of perovskite solar cells (PSCs). The residual PbI<sub>2</sub> exists in its crystalline hexagonal phase, distributed along the perovskite grain boundaries. However, it is also known that the presence of this crystalline PbI<sub>2</sub> is a double-edged sword, and sacrifices the long-term operational stability of PSCs. Under illumination, PbI<sub>2</sub> can undergo photolysis to decompose into metallic Pb and I<sub>2</sub> gas – the former constitutes a deep-level trap state, while the latter aggravates the perovskite phase degradation.<br/><br/>In this work, we demonstrate a strategy to suppress the crystallization of residual PbI<sub>2</sub>. Synchrotron-based in-situ wide-angle X-ray scattering (in-situ WAXS) measurements were used to monitor the perovskite formation from solution and during thermal annealing, confirming the amorphization of PbI<sub>2</sub> into a secondary, non-crystalline phase. We observed that this amorphization of PbI<sub>2 </sub>significantly improved the ambient, humidity, and photo stability of the perovskite thin films. Control experiments on perovskites with residual crystalline PbI<sub>2</sub> showed reduced or comparable stability under the same testing conditions. We verified the universality of our results on a variety of different perovskite compositions. Lastly, our champion devices also reached power conversion efficiencies approaching 25%, with an open-circuit voltage (V<sub>OC</sub>) loss as low as 0.33 V.