Abstract
A two-step-solution-processing approach has been established to grow void-free perovskite films for low-cost and high-performance planar heterojunction photovoltaic devices. A high-temperature thermal annealing treatment was generally applied to drive the diffusion of CH3NH3I precursor molecules into the compact PbI2 layer to form perovskite films. However, thermal annealing for extended periods would lead to degraded device performance due to the defects generated by decomposition of perovskite into PbI2. In this work, we explored a controllable layer-by-layer spin-coating method to grow “bilayer” CH3NH3I/PbI2 films, and then drive the interdiffusion between PbI2 and CH3NH3I layers by a simple room-temperature-air-exposure for making well-oriented, highly-crystalline perovskite films without thermal annealing. This high degree of crystallinity resulted in a carrier diffusion length of ~ 800 nm and high device efficiency of 15.0±0.4%, which is comparable to the reported values from thermally-annealed perovskite films based counterparts. The simplicity and high device performance of this processing approach is highly promising for direct integration into industrial-scale device manufacture.
