Insights from Planar Heterojunctions: Understanding Charge Carrier Generation in Organic Photovoltaics

Organic photovoltaics (OPVs) have recently achieved high short-circuit current densities (J_SC) approaching 30 mA/cm² with internal quantum efficiencies surpassing 90%. In comparison to their inorganic or perovskite counterparts, a distinguishing feature of OPVs is the involvement of singlet or charge-transfer excitons in photoelectron conversion. A deeper understanding of the charge generation process with these excitons is crucial to further enhance J_SC while maintaining the open-circuit voltage and fill factor. In this perspective, we provide new insights into the charge generation mechanisms and their electric field dependence derived from investigations using planar heterojunction structures and their comparison to bulk heterojunction systems. We aim to foster open discussion and collaboration within the research community to address the aforementioned challenges.