• Rai, Nitish
• Saripally, Sudhaker
• Weerarathna, K. Lakshani Jayaprada
• Simonov, Alexandr
• Bach, Udo

Abstract

Interfacial defects between the organic-inorganic lead halide perovskite and hole transporting layers are one significant factor limiting performance of the perovskite solar cells (PSCs). These defects typically result from either lead or halide atom vacancies or under-coordinated Pb2+ atoms, which act as recombination centres for holes. To address this, we demonstrate that a thin layer of a polybithiophene-ester (PBTE) or a polyterthiophene-diester (PTTDE) introduced between the FA0.92MA0.08Pb(I0.92Br0.08)3 (MA+ = methylammonium; FA+ = formamidinium) perovskite layer and spiro-OMeTAD hole transporting layer (HTL) improves device stability and power-conversion efficiency (PCE). The PCE improvements are primarily associated with an enhanced open-circuit voltage and fill-factor arising from Lewis-base passivation of under-coordinated Pb2+ defects through interaction with the polymer carbonyl groups, as well as enhanced charge transfer between the perovskite layer and HTL facilitated by the conjugated thiophene functionalities of the polymeric interlayer. Furthermore, coating perovskite films with these thiophene-based polymers improves their thermal and moisture stability. Encapsulated PSCs comprising PTTDE or PBTE interlayers retain their initial PCE after 1440 hours at 65 °C and under 0.5-sun irradiation, while PSCs without a polymeric interlayer lose around 50% of their initial PCE. These results can guide future designs of ester-functionalised thiophene-based polymeric interlayers for high-performance PSCs.

Topics

• perovskite
• polymer
• defect
• interfacial
• ester