Drop‐Casting to Make Efficient Perovskite Solar Cells under High Humidity

Drop‐casting was used to make MAPbI 3 films for solar cells. The crystal growth in drop‐cast MAPbI 3 films was regulated by adjusting temperature. A mechanism for the formation of different morphology was proposed by combining in situ crystal‐growth study with XRD measurements. The crystals in the films made at low temperature (60 °C) and high temperature (≥120 °C) are (110) and (200) oriented, respectively. The different crystal growth mode leads to quite different film morphology. Compared with spin‐coating, drop‐casting shows much better tolerance to humidity. MAPbI 3 solar cells made under 88 % humidity delivered a PCE of 18.17 %, which is the highest PCE for perovskite solar cells made under >70 % humidity without antisolvent assistance.