High Performance Inverted Organic Photovoltaics Without Hole Selective Contact

TL;DR

This study demonstrates that inverted organic photovoltaics can achieve high efficiency and stability without hole transporting layers by using bare silver contacts and ambient oxygen exposure, simplifying device architecture.

Contribution

It introduces a novel approach of using bare Ag contacts and ambient oxygen to eliminate the need for hole transporting layers in inverted OPVs, maintaining high efficiency and stability.

Findings

Achieved over 3.5% PCE after 4 days air exposure.

Demonstrated 6.5% PCE with various polymer:fullerene systems.

Showed comparable stability to traditional devices under damp heat conditions.

Abstract

A detailed investigation of the functionality of inverted organic photovoltaics (OPVs) using bare Ag contacts as top electrode is presented. The inverted OPVs without hole transporting layer (HTL) exhibit a significant gain in hole carrier selectivity and power conversion efficiency (PCE) after exposure in ambient conditions. Inverted OPVs comprised of ITO/ZnO/poly(3-hexylthiophene-2,5-diyl):phenyl-C61-butyric acid methyl ester (P3HT:PCBM)/Ag demonstrate over 3.5% power conversion efficiency only if the devices are exposed in air for over 4 days. As concluded through a series of measurements, the oxygen presence is essential to obtain fully operational solar cell devices without HTL. Moreover, accelerated stability tests under damp heat conditions (RH=85% and T=65oC) performed to non-encapsulated OPVs demonstrate that HTL-free inverted OPVs exhibit comparable stability to the reference inverted OPVs. Importantly, it is shown that bare Ag top electrodes can be efficiently used in inverted OPVs using various high performance polymer:fullerene bulk heterojunction material systems demonstrating 6.5% power conversion efficiencies.