Publication date: 1st July 2014
Structure control in solution-processed hybrid perovskites is crucial to design and fabricate highly efficient solar cells. Here, we utilize in situ grazing incidence wide-angle X-ray scattering (GIWAXS) and scanning electron microscopy to investigate the structural evolution and film morphologies of methylammonium lead mixed halide perovskite during thermal annealing. We show that the material evolution can be characterized by three distinct structures: a crystalline precursor structure not described previously, a 3D perovskite structure, and a mixture of compounds resulting from degradation. Finally, we demonstrate how understanding the processing parameters provides the foundation needed for optimal perovskite film morphology and coverage.Based on this, we investigated the photovoltaic device performance with planar heterojunction architectures under different annealing conditions. We observed that a short rapid thermal annealing at 130 °C leads to the growth of large micron-sized textured perovskite domains and improved short circuit currents and power conversion efficiencies up to 13.5% for planar heterojunction perovskite solar cells.This work highlights the criticality of controlling the thin film crystallization mechanism of hybrid perovskite materials and offers a simple pathway for further enhancements in perovskite solar cells.