Enhanced performance in hole transport material free perovskite solar cells via morphology control of PbI2 film by solvent treatment

•A simple solvent treatment process is introduced.•Morphology of PbI2 film is modified by the solvent treatment.•More complete conversion of PbI2 to CH3NH3PbI3 is observed.•Enhanced performance and reproducibility is obtained.

The morphology of PbI2 film plays a critical role in determining the quality of the resultant CH3NH3PbI3 film and power conversion efficiency of CH3NH3PbI3 perovskite solar cell. Here, we propose a solvent treatment method in the two-step sequential deposition process to control the morphology of PbI2 film, which leads to enhanced power conversion efficiency. Hole transport material free perovskite solar cell is chosen as a paradigm to demonstrate this idea. Solvent (isopropanol, chlorobenzene, or ethanol) treated PbI2 films exhibit dendrite-like or flake-like morphologies, which facilitate more complete conversion of PbI2 to CH3NH3PbI3 perovskite in ambient atmosphere with a relative high humidity. Therefore, enhanced performance is obtained with the solvent treated PbI2 films. Average power conversion efficiency has been improved from 9.42% in the traditional two-step sequential deposition to 11.22% in solar cells derived from ethanol treated PbI2 films.