Investigating the Structural Changes of Mixed Halide Perovskites Treated with Contact Layers

Mixed-halide perovskites have garnered immense scientific interest since the first implementation of the semiconductor in a photovoltaic cell in 2009. This is due to their many desirable properties such as their tunable bandgap, defect tolerance, and inexpensive fabrication. Widespread use of perovskites is hindered by the discrepancy between their theoretical and experimental efficiencies. A main contributor to this is the segregation of the halides within the perovskite forming low bandgap domains that act as traps in the material under illumination. Experimental data suggests contact layers could improve the stability of perovskites under light. Utilizing grazing-incidence wide angle x-ray scattering at the Stanford Synchrotron Radiation Lightsource, we were able to observe structural changes of MaPbBrI2 treated with either the hole-transport layer (HTL) poly(trairly amine) (PTAA) or the electron-transport layer (ETL) fullerene (C60) under continuous wave conditions in situ; with the ultimate goal of using such contacts to suppress photoinduced halide segregation. Our results indicate that contact layers play a role in the structural stability of our device. The HTL sample showed the emergence of multiple crystalline domains, while the perovskite with an ETL layer did not.