Organic solar cells (OSCs) are promising photovoltaic technology that can play a key role in a future for low-cost energy generation. Organic solar cells can be thin, light-weight, highly transparent, and mechanically flexible providing new opportunities for their integration into buildings, wear, etc. Furthermore, OSCs can be fabricated using printable methods, which are compatible with high-throughput R2R technology. Most importantly, the power conversion efficiency (PCE) of OPV has significantly increased over the last years, reaching a record above 18%. However, the organic materials makes the solar cells susceptible to degradation caused by environmental stresses such as oxygen, heat, light, and humidity. Although encapsulation of these devices can mitigate or even completely eliminate some of the listed adverse effects, overcoming these limitations at the molecular level is the most desirable solution for this problem.

In this work, we present the investigation of outdoor stability of polymer-fullerene organic solar cells (OSCs) using naphthalene dithiol (NDT) as a stabilizing additive. We studied the effect of NDT on recombination processes in OSCs. The operational stability of OSCs was evaluated under real outdoor conditions (Sede Boker in the Negev desert, Israel, latitude, 30.8°N; longitude, 34.8°E; altitude, 475 m), following the ISOS-O-1 protocol during September 2019, with the exposure of the OSCs samples for 10 days. The average day-time light intensity during the experiment was 65 mW cm^–2 at ambient temperatures not exceeding 40 °C.

Utilizing of NDT additive in active layer can efficiently reduce the number of traps, which was demonstrated by increase in the photocurrents of devices. Besides, NDT prevents the formation of new traps and subsequent recombination process, which was confirmed by TPV and TPC techniques. Moreover, the OSCs comprising benzodithiophene-based conjugated polymer P1 and fullerene derivative [60]PCBM, which were stabilized by adding of NDT, exhibited both excellent stability and capability of recovering. For example, the devices with NDT additive exhibited a small drop in characteristic for the first 70–100 h with further recovery of the performance. After 10 day of operation, the efficiency of the devices decreased by less than 10% that is two times lower than for non-stabilized devices. Thus, NDT has been confirmed as the promising stabilizing component for OSCs that is of great interest for practical applications.