Fabrication of high quality perovskite films by modulating the Pb–O bonds in Lewis acid–base adducts

High efficiency perovskite solar cells can be made through the Lewis adduct approach. The interaction between PbI2 and the Lewis base is a key factor to make high quality perovskite films. Here, we combine a two-step method with the Lewis adduct approach to fabricate high quality organometallic perovskite films by tuning the strength of the Pb-O bond in Lewis acid-base adducts via adding different Lewis base additives. By optimizing the strength of the Pb-O bond, smooth CH3NH3PbI3 films with large perovskite grains are prepared. The high quality CH3NH3PbI3 films lead to a low recombination rate, long carrier life time and highly efficient charge transfer process. As a result, the power conversion efficiency of the best perovskite solar cell increases from 12.79% to 17.26%.