The emergence of the Internet of Things (IoT) and the increasing demand for connected and intelligent devices[1], have sparked interest in utilizing Organic Photovoltaic (OPV) technology for indoor applications. OPVs possess unique properties such as tunable absorption, flexibility, low cost, lightweight, colouration, and large-area processability, making them highly desirable for addressing the demands of IoT [2].

However, the urgency of global environmental concerns calls for greener processes and the search for suitable alternatives to halogenated solvents and toxic additives [3]. To explore the potential of OPVs and their future industrialization, it is crucial to develop environmentally friendly ink formulations compatible with various deposition techniques. we have addressed these challenges by optimizing an indoor-adapted OPV system based on a non-fullerene acceptor using non-halogenated solvents such as o-xylene in combination with additives such as 1,8-diiodooctane (DIO) or tetralin. Indeed, we have shown that adding tetralin to PM6: ITIC-4F blend dissolved in o-xylene strongly enhances the layer morphologies of inkjet-printed layers in air. This led to printed solar cells with efficiencies of 10% using less toxic solvents[4]. However, although tetralin was used at 3% in the ink formulation it is known as rather a toxic solvent [5][6] making the seek for less toxic additives important to enhance the industrial potential of printed OPV.

In this work, we present our results on replacing tetralin with a much less toxic additive usually used for fullerene acceptors[7][8]. Indeed, we show here that diphenyl ether (DPE) is a highly suitable additive for NFA that simultaneously enhances layer processing and structural order inside the acceptor phase. Combined DPE with a concentration of up to 20% with o-xylenes allows us to process solar cells based on ITIC-4F and FCC-Cl NFA leading to power conversion efficiency (PCE) values approaching 20% under indoor illumination of 1000 lux.

Furthermore, we explored the air processability of our formulations using the doctor blade technique and inkjet printing at the cell and module scale. Additionally, we conducted a comprehensive analysis of the cells, encompassing morphological, optical, and electrical characterizations to gain insights into the impact of different formulations and deposition techniques on efficiency and physical properties.