Thickness dependent effects of an intermediate molecular blocking layer on the optoelectronic characteristics of organic bilayer photovoltaic cells

TL;DR

This study investigates how the thickness of a molecular blocking layer affects the performance of organic bilayer photovoltaic cells, revealing an optimal layer thickness that significantly improves efficiency.

Contribution

It demonstrates the microscopic effects of an intermediate BPhen layer on exciton blocking, metal penetration, and electron transport in organic photovoltaic cells.

Findings

Optimal BPhen thickness of 5 nm enhances efficiency by over twofold.

Ag atoms penetrate the C60 layer without blocking, affecting exciton quenching.

Balancing exciton blocking and metal penetration improves device performance.

Abstract

In this work we address the microscopic effects related to the implementation of a Bathophenanthroline (BPhen) exciton blocking layer (EBL) sandwiched between Ag cathode and molecular Diindenoperylene (DIP)/C60 bilayer of a photovoltaic cell. Complementary studies of current density, external quantum efficiency, and photoluminescence quenching for EBL thicknesses up to 50 nm indicate that Ag atoms are able to penetrate through the whole 35 nm thick C60 film into the crystalline DIP layer underneath, thereby enhancing exciton quenching if no blocking layer is applied. In contrast, an optimal trade-off between exciton blocking, suppression of metal penetration and electron transport is achieved for a 5 nm thick BPhen layer yielding an improvement of power conversion efficiency by more than a factor of 2.