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

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.