||Perovskite solar cells prepared by a new 3-step method including a PbI 2 scavenging step
Okamoto, YujiSuzuki, Yoshikazu
Materials science in semiconductor processing
6 , 2017-11 , Elsevier
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−xBrx. Morphological improvements such as a network formation among perovskite grains and a decrease of intergranular voids were also observed. The additional CH3NH3I spin-coating resulted in the increases of both JSC and VOC, 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 ~ 85% of the original PCE values after storing in air for 700 h, which indicates an improved stability.