A Unified Diode Equation for Organic Photovoltaic Devices

TL;DR

This paper introduces a comprehensive diode equation for organic photovoltaics that incorporates charge injection, extraction, and recombination effects, validated through simulations and experiments, enhancing understanding of device physics.

Contribution

The authors develop a unified analytical diode model for OPVs that accounts for charge injection, extraction, and bimolecular recombination, addressing limitations of previous models.

Findings

Model accurately predicts current-voltage behavior.

Validated with numerical simulations and experimental data.

Provides insights into charge transport and recombination in OPVs.

Abstract

Organic photovoltaics (OPVs) are promising candidates for future sustainable technologies, including applications within the renewable energy sector, such as solar cells and indoor light recycling, and photodetection. However, the performance of OPVs is still inferior compared to established technologies, partially due to the intrinsically low charge carrier mobilities and large recombination losses in the low-permittivity, molecular organic semiconductors. To better understand these losses, accurate analytical diode models capable of capturing the underlying device physics are imperative. However, previously proposed analytical models have neglected the effects of injected charge carriers, which is the predominant source for bimolecular recombination in thin-film systems with ohmic contacts. In this work, we derive a unified diode equation for current in OPVs, which accounts for the interplay between charge carrier extraction, injection, and bimolecular recombination. To this end, we use a regional approximation approach to solve the coupled charge transport equations in sandwich-type thin film devices. The diode model is further validated by numerical simulations and experimental data. The derived theoretical framework not only provides vital insights into the underlying device physics of OPVs but is generally applicable to sandwich-type thin-film photovoltaic device based on semiconductors with low charge carrier mobilities.