Role of Polaron Pair Diffusion and Surface Losses in Organic Semiconductor Devices

TL;DR

This paper investigates how polaron pair diffusion and surface losses affect the efficiency of organic semiconductor devices, using simulations and a unified analytical model to understand and mitigate these loss mechanisms.

Contribution

It introduces a comprehensive analytic model combining Onsager theory, Sokel-Hughes model, and polaron diffusion to better understand loss mechanisms in organic photovoltaic devices.

Findings

Polaron pair extraction at electrodes is a significant efficiency loss.

The unified model accurately describes polaron dissociation and extraction.

Insights from the model can guide optimized device design.

Abstract

By applying Monte Carlo simulations we found that the extraction of bound polaron pairs (PP) at the electrodes is an important loss factor limiting the efficiency of organic optoelectronic and photovoltaic devices. Based upon this finding, we developed a unified analytic model consisting of exact Onsager theory, describing the dissociation of PP in organic donor-acceptor heterojunctions, the Sokel-Hughes model for the extraction of free polarons at the electrodes, as well as of PP diffusion leading to the aforementioned loss mechanism, which was not considered previously. Our approach allows to describe the simulation details on a macroscopic scale and to gain fundamental insights, which is important in view of developing an optimized photovoltaic device configuration.