Semitransparent Organic Photovoltaics Utilizing Intrinsic Charge Generation in Non‐Fullerene Acceptors

Abstract

AbstractIn organic semiconductors, a donor/acceptor heterojunction is typically required for efficient dissociation of excitons. Using transient absorption spectroscopy to study the dynamics of excited states in non‐fullerene acceptors (NFAs), it is shown that NFAs can generate charges without a donor/acceptor interface. This is due to the fact that dielectric solvation provides a driving force sufficient to dissociate the excited state and form the charge‐transfer (CT) state. The CT state is further dissociated into free charges at interfaces between polycrystalline regions in neat NFAs. For IEICO‐4F, incorporating just 9 wt% donor polymer PTB7‐Th in neat films greatly boosts charge generation, enhancing efficient exciton separation into free charges. This property is utilized to fabricate donor‐dilute organic photovoltaics (OPV) delivering a power conversion efficiency of 8.3% in the case of opaque devices with a metal top‐electrode and an active layer average visible transmittance (AVT) of 75%. It is shown that the intrinsic charge generation in low‐bandgap NFAs contributes to the overall photocurrent generation. IEICO‐4F‐based OPVs with limited PTB7‐Th content have high thermal resilience demonstrating little drop in performance over 700 h. PTB7‐Th:IEICO‐4F semitransparent OPVs are leveraged to fabricate an 8‐series connected semitransparent module, demonstrating light‐utilization efficiency of 2.2% alongside an AVT of 63%.