Perovskite solar cells prepared by a new 3-step method including a PbI2 scavenging step

摘要

CH3NH3PbI3 films prepared by the 2-step method for perovskite solar cells generally have problems of residual unreacted PbI2 and rough surface structure. Here, we report a new 3-step method, based on the 2-step method with an additional spin-coating of CH3NH3(I,Br) solution on the CH3NH3PbI3 film to scavenge remnant PbI2. The 3-step method improved light absorption of the film by converting the residual PbI2 into CH3NH3PbI3-x,Br-x. Morphological improvements such as a network formation among perovskite grains and a decrease of inter granular voids were also observed. The additional CH3NH3I spin-coating resulted in the increases of both J(sc) and V-oc, while that of CH3NH3Br solution showed a slight decrease of Jsc and large increase of Voc due to the enlarged bandgaps. The maximum power conversion efficiency was improved from 12.9% (2-step) to 14.4% (3-step). Furthermore, the 3-step cells retained similar to 85% of the original PCE values after storing in air for 700 h, which indicates an improved stability.