Field-enhanced recombination at low temperatures in an organic photovoltaic blend

TL;DR

This study reveals that in organic photovoltaic blends at low temperatures, an external electric field can enhance charge recombination due to field-assisted separation of electron-hole pairs at donor-acceptor interfaces, challenging conventional understanding.

Contribution

The paper introduces a microwave resonance technique to monitor low-temperature charge recombination and demonstrates the counterintuitive effect of electric fields increasing recombination in organic solar cells.

Findings

Electric field can increase recombination at low temperatures.

Recombination depends on initial electron-hole separation.

Monte Carlo simulations explain the field-assisted separation mechanism.

Abstract

We report on the non-trivial field dependence of charge carrier recombination in an organic blend at low temperatures. A new microwave resonance technique for monitoring charge recombination in organic semiconductors at low temperatures is applied in bulk heterojunction P3HT:PCBM blends with results showing that an external electric field can in fact increase recombination. Monte Carlo simulations suggest that this contradiction to conventional wisdom relates to electron-hole pairs that are separated at donor-acceptor interfaces where the electric field acts in synergy with their Coulomb attraction. For this behaviour to occur a critical initial separation of 5nm between the carriers is required.