| AVS 66th International Symposium & Exhibition | |
| Thin Films Division | Thursday Sessions |
| Session TF+AS+EL+PS+RA-ThA |
| Session: | Characterization of Thin Film Processes and Properties |
| Presenter: | Jonathan Meyers, University of North Carolina at Chapel Hill |
| Authors: | J.K. Meyers, University of North Carolina at Chapel Hill L.Y. Serafin, University of North Carolina at Chapel Hill J.F. Cahoon, University of North Carolina at Chapel Hill |
| Correspondent: | Click to Email |
Lead halide perovskites have shown remarkable promise for use in thin film optoelectronic devices such as photodetectors, light-emitting diodes, and solar cells. Methods for casting thin films of perovskite have been extensively studied, and great improvements have been made in an effort to improve device efficiency and stability. A few reports have suggested some benefits to processing or post-processing techniques in a methylamine (MA) atmosphere, including healing grain boundary defects to create pinhole free films with grains on the order of tens of microns and improving crystallinity. The process can be observed spectroscopically as the MA induces a reversible phase change which bleaches the dark perovskite film. In this work, we perform the MA-treatment in a vacuum reactor while monitoring in-situ the UV-visible spectral response correlated with temperature and MA partial pressure. Clear evidence is found for the existence of a solid intermediate phase in transitioning from MAPbI3(s) to MAPbI3*xMA(l) and back again. We construct a phase diagram and demonstrate that the critical partial pressure of the phase transition changes from 10 to 500 torr between 25 and 120 °C. By tuning the kinetics of film crystallization, compact films with domains up to 80 μm can be produced.