PTQ10:L8-BO Organic Photoactive Layers Enable Improved Stability for Solar Water Oxidation and Enhanced Unassisted Water Splitting

Abstract

Integrating organic photovoltaics into anodes (IPV-anodes) represents a promising way to exploit the excellent optoelectronic properties of organic polymer:non-fullerene bulk-heterojunctions (BHJ) for solar-to-fuel applications. However, the high voltage losses, poor photochemical stability and high synthetic complexity of the most commonly used polymer:non-fullerene combinations have limited their full potential. Here, we address these limitations by introducing a BHJ comprising the low-synthetic-complexity polymer PTQ10 and the near-infrared absorbing acceptor L8-BO. By integrating this new BHJ with a graphite sheet functionalised with a NiFeOOH catalyst, we achieve a low onset potential of +0.64 VRHE, a photocurrent density of 21 mA cm−2 at +1.23 VRHE and a t80 operational stability of 22 h under full AM1.5G illumination (i.e., without using any UV filter) for water oxidation. These values represent a 40 mV increase in photovoltage and a sevenfold improvement in operational stability (t80 extended from 3 h to 22 h) compared to reference IPV-anodes based on the ternary D18:PM6:L8-BO photoactive blend. Spectroscopic analyses reveal that these improvements stem from the reduced non-radiative voltage losses (from 0.24 V to 0.19 V) and superior photochemical and morphological stability of the PTQ10:L8-BO blend compared to the reference blend. Building on these advances, we demonstrate monolithic tandem IPV-anodes integrating PTQ10:IDIC and PTQ10:L8-BO organic blends to achieve a solar-to-hydrogen efficiency of 6.2%, offering critical insights for boosting the stability and efficiency of integrated solar-to-hydrogen systems working without any external bias.