S-shaped current-voltage characteristics of organic solar devices

TL;DR

This paper investigates the origin of s-shaped current-voltage curves in organic solar cells, linking surface recombination and interface effects to device performance, and demonstrates experimental methods to induce these characteristics.

Contribution

It provides a numerical model explaining s-shaped I-V curves due to reduced surface recombination and experimentally shows how plasma etching induces these effects in organic solar devices.

Findings

S-shaped I-V curves linked to surface recombination effects

Plasma etching of ITO induces s-shaped characteristics

Implications for open circuit voltage discussed

Abstract

Measuring the current-voltage characteristic of organic bulk heterojunction solar devices sometimes reveals an s-shaped deformation. We qualitatively produce this behaviour by a numerical device simulation assuming a reduced surface recombination. Furthermore we show how to experimentally create these double diodes by applying an oxygen plasma etch on the indium tin oxide (ITO) anode. Restricted charge transport over material interfaces accumulates space charges and therefore creates s-shaped deformations. Finally we discuss the consequences of our findings for the open circuit voltage $V_{oc}$