Free charge photogeneration in a single component high photovoltaic efficiency organic semiconductor

Organic photovoltaics (OPVs) offer a promising pathway to cost-effective and flexible solar energy. Unlike silicon photovoltaics where light generates free charges, organic semiconductors typically form excitons due to their low dielectric constants, necessitating molecular heterojunctions for charge separation. This study demonstrates that the high dielectric constant of the small molecule Y6 allows for intrinsic free charge generation in Y6 films without a heterojunction. Spectroscopic analyses reveal that 60-90% of excitons dissociate into free charges at AM1.5 intensity. While bimolecular recombination and hole traps limit single-component Y6 photovoltaic efficiency, adding small amounts of donor material reduces recombination. Quantum-chemical calculations show strong exciton-CT state coupling and an intermolecular polarization pattern that facilitates exciton dissociation. This challenges conventional understanding of OPV operation and revives the potential of efficient single-component OPVs.

Michael B. Price, Paul A. Hume, Aleksandra Ilina, Isabella Wagner, Ronnie R. Tamming, Karen E. Thorn, Wanting Jiao, Alison Goldingay, Patrick J. Conaghan, Girish Lakhwani, Nathaniel J. L. K. Davis, Yifan Wang, Peiyao Xue, Heng Lu, Kai Chen, Xiaowei Zhan, Justin M. Hodgkiss