Solvent-Mediated Intragranular-Coarsening of CH3NH3PbI3 Thin Films toward High-Performance Perovskite Photovoltaics.

The deposition of dense and uniform perovskite films with large grains is crucial for fabricating high-performance perovskite solar cells (PSCs). High-quality CH3NH3PbI3 films were produced by a self-induced intragranular-coarsening approach. The perovskite precursor solution contained a Lewis base, N,N-dimethyl sulfoxide (DMSO), and was deposited using a gas-assisted, one-step, spin-coating method that was followed by a solvent vapor-assisted annealing treatment using a mix of DMSO and chlorobenzene (CBZ). Combining solvent-engineering with gas-assisted deposition helps to form intermediate crystalline entities upon evaporation of the parent solvent but retards the otherwise fast reaction between the precursor ingredients. Subsequent cosolvent annealing induces further grain-coarsening via a facilitated dissolution-precipitation process. This technique produced flat CH3NH3PbI3 films featuring large grain microstructures, with well-coarsened subgrains and a reduction of intragranular defects that minimized carrier recombination. The optimized CH3NH3PbI3 films exhibited enhanced crystallinity, excellent carrier transport and injection, as well as suppressed charge recombination. Benefiting from these advantages, PSCs based on the optimized perovskite films delivered a power conversion efficiency of 17.99% and a stabilized power output above 17.30%. This study presents an effective strategy for the fabrication of high-quality, hybrid perovskite films with potential applications in optoelectronic devices.