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.