Interface Engineering with Polymer Hole Transport Layer for 3D Perovskite Solar Cells

Perovskite solar cells have demonstrated impressive efficiency, but their susceptibility to moisture ingress and ion-transport must be reduced in order to attain a lifetime sufficient for a commercially viable photovoltaic technology. New approaches have been used to create PSCs, including with triple cation absorbers, lowering the dimensionality of the absorber or alternate electrode layers, in order to address the stability issue. Another way in which stability is enhanced is via interface engineering to block moisture access to the hygroscopic photoabsorbers used in PSCs. 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% in case of using PTAA to 12.73% by using PTB7.