One-step Preparation of ZnO Electron Transport Layers Functionalized with Benzoic Acid Derivatives

TL;DR

This paper introduces a simple one-step method to functionalize ZnO electron transport layers with benzoic acid derivatives, enhancing performance and stability in organic solar cells while simplifying manufacturing.

Contribution

The study presents a novel one-step surface modification technique for ZnO ETLs using BZA derivatives, improving device efficiency and stability without complex processing.

Findings

Enhanced device performance with BZA-treated ZnO layers.

Improved stability of organic solar cells using the new method.

Surface properties of ZnO are effectively modified by BZA derivatives.

Abstract

We present a "one-step" approach to modify ZnO electron transport layers (ETLs) used in organic solar cells. This approach involves adding benzoic acid (BZA) derivatives directly to the ZnO precursor solution, which are then present at the surface of the resulting ZnO film. We demonstrate this approach for three different BZA derivatives, namely benzoic acid, chlorobenzoic acid, and 4-hydrazinobenzoic acid. For all molecules, improved device performance and stability is demonstrated in solar cells using an active layer blend of PTQ10 (donor) and ITIC-Br (non-fullerene acceptor) compared to such cells prepared using untreated ZnO. Furthermore, similar or improved device performance and stability is demonstrated compared to conventional PEIE treatment of ZnO. The presence of the BZA derivatives at the surface after processing is established using X-ray photoelectron spectroscopy and near-edge X-ray absorption fine-structure spectroscopy. From atomic force microscopy analysis and X-ray diffraction studies, the addition of BZA derivatives appears to restrict ZnO grain growth; however, this does not negatively impact device performance. ZnO layers treated with BZA derivatives also exhibit higher water contact angle and lower work function compared to untreated ZnO. This approach enables simplification of device manufacture while still allowing optimization of the surface properties of metal oxide ETLs. Keywords: electron transport layers, zinc oxide, organic solar cells, surface modification