Wide Bandgap Organic Solar Cells with Improved Photovoltaic Performance via Solid Additive Integration

Abstract

Wide bandgap (WBG) and high-voltage organic solar cells (OSC) are of high interest for applications such as top cell in multijunction structures and indoor photovoltaic. In this study, an inverted WBG OSC is optimized through a synergistic approach integrating material design and a solid additive strategy. The initial active layer is composed of a blend of the WBG donor polymer PBDB-T-2F (PM6) with a WBG non-fullerene acceptor (NFA) GS-ISO. After optimization of the process, including thermal annealing of the active layer and incorporation of processing additives, a power conversion efficiency (PCE) of 7.4% is reached. It is shown that the introduction of a conjugated polymer, F8T2, in small quantities (less than 1% wt), further improves the photovoltaic performances. Indeed, the effects of enhanced absorption through improved intermolecular packing result in a high open-circuit voltage (VOC) of 1.20 V and a fill factor (FF) of 0.68, leading to a PCE of 10 % for the champion cell under 1 sun. Such a WBG cell is particularly suitable to be integrated as top cell in a full-OSC lateral multijunction architecture and we show theoretical achievable efficiencies up to 14% and values of increase-over-best-cell (IoBC) up to 21%. Beyond multijunction applications, WBG materials are also of particular interest in the development of efficient indoor photovoltaic devices, and the cells developed in this work were proven to reach efficiencies up to 16% under 1000 lx illumination.