Low-temperature, simple and efficient preparation of perovskite solar cells using Lewis bases urea and thiourea as additives: stimulating large grain growth and providing a PCE up to 18.8.

We demonstrated that two Lewis bases - urea and thiourea - acted as efficient additives for CH 3 NH 3 (MA)PbI 3- x Cl x and MAPbI 3 perovskite solar cells (PSCs) and observed a significant increase in PCE for the MAPbI 3 devices in the presence of 1% urea with a remarkable PCE of 18.8% using an extremely low annealing temperature (85 °C).