Interface engineering with polymer hole transport layer for 3D perovskite solar cells

Perovskite solar cells demonstrate impressive efficiency, but their susceptibility to moisture ingress and ion-transport must be reduced to attain a lifetime sufficient for a commercially viable photovoltaic technology. A new approach in which stability is enhanced is via interface engineering to block moisture access to the hygroscopic photo-absorbers used in perovskite solar cells. In this work, we explored the use of polymer interface layers between the 3D perovskite absorber and the conventional hole transport layer, Spiro-OMeTAD. Specifically, poly-[bis-(4-phenyl)-(2,4,6-trimethylphenyl)-amin] (PTAA) and Poly({4,8-bis[(2-ethylhexyl)oxy]benzo[1,2-b:4,5-b′]dithiophene-2,6-diyl}{3-fluoro-2-[(2-ethylhexyl)carbonyl]thieno[3,4-b]thiophenediyl}) (PTB7) were examined in the regular structure, but these are mostly utilized as hole transporting layers in an inverted structure. Specifically, the effect of inserting PTAA and PTB7 layers, as buffer layers at the interface between the absorber layer and hole transporting layer in perovskite solar cells is investigated. The power conversion efficiency of perovskite solar cells decreased from 16.49% when using PTAA to 12.73% using PTB7.