Quantum Mechanical Assessment of Optimal Photovoltaic Conditions in Organic Solar Cells

TL;DR

This study uses quantum mechanical modeling to identify optimal conditions for charge generation in organic solar cells, highlighting the roles of energetic driving force, Coulomb interaction, and external bias in minimizing energy losses.

Contribution

The paper introduces a coarse-grained quantum model to analyze charge generation dynamics under various energy loss mechanisms in organic photovoltaics.

Findings

Energy losses are minimized when driving force approaches reorganization energy.

Charge generation is insensitive to temperature and electric field near optimal conditions.

Moderate reverse bias reduces geminate recombination at low driving forces.

Abstract

Recombination losses contribute to reduce $J_{SC}$, $V_{OC}$ and the fill factor of organic solar cells. Recent advances in non-fullerene organic photovoltaics have shown, nonetheless, that efficient charge generation can occur under small energetic driving forces ($\Delta E_{DA}$) and low recombination losses. To shed light on this issue, we set up a coarse-grained open quantum mechanical model for investigating the charge generation dynamics subject to various energy loss mechanisms. The influence of energetic driving force, Coulomb interaction, vibrational disorder, geminate recombination, temperature and external bias are included in the analysis of the optimal photovoltaic conditions for charge carrier generation. The assessment reveals that the overall energy losses are not only minimized when $\Delta E_{DA}$ approaches the effective reorganization energy at the interface but also become insensitive to temperature and electric field variations. It is also observed that a moderate reverse bias reduces geminate recombination losses significantly at vanishing driving forces, where the charge generation is strongly affected by temperature.