Organic photovoltaic bulk heterojunctions with spatially varying composition

TL;DR

This paper models organic bulk heterojunction photovoltaics with spatially varying compositions, revealing that composition variations mainly influence charge generation rather than transport, and a donor-rich skin layer has minimal impact on performance.

Contribution

It introduces analytical and numerical models for spatially varying compositions in organic photovoltaics, highlighting the limited effect of composition variation on charge transport and device efficiency.

Findings

Variation in blend composition minimally affects charge transport.

A donor-rich skin layer has a small impact on device performance.

The geometry of the blend influences photocharge generation.

Abstract

Models of organic bulk heterojunction photovoltaics which include the effect of spatially varying composition of donor/acceptor materials are developed and analyzed. Analytic expressions for the current-voltage relation in simplified cases show that the effect of varying blend composition on charge transport is minimal. Numerical results for various blend compositions, including the experimentally relevant composition of a donor-rich region near the cathode (a "skin layer" of donor material), show that the primary effect of this variation on device performance derives from its effect on photocharge generation. The general relation between the geometry of the blend and its effect on performance is given explicitly. The analysis shows that the effect of a skin layer on device performance is small.