Effect of PEIE and polylysine as interfacial layers on the performance of air-processed organic solar cells under both indoor and 1 sun conditions

Organic solar cells (OSCs) are showing great potential to be employed in indoor and outdoor applications. The utilization of portable electronics, internet of things (IoT), and sensors for wearable and healthcare applications that are used in both indoor and outdoor conditions highlight the importance of the development of photovoltaic devices that can efficiently perform under various light intensities. In this paper, we fabricated OSCs with polyethyleneimine ethoxylated (PEIE) and a water-based material, polylysine, as interfacial layers (IFL), and investigated the devices' performance under 1 sun and indoor light. Our results show that the choice of the interfacial layer is important and affects significantly the performance of devices. Under 1 sun illumination devices with polylysine as an interfacial layer exhibit the highest average efficiency of 7.72% whereas PEIE-based devices displayed a lower average efficiency of 7.13%. When moving to indoor illumination (1000 lx) the performance of the two devices are inverted: polylysine-based devices demonstrated reduced average efficiency (7.09%) compared to their 1 sun illumination results while PEIE-based devices achieve an increased average efficiency of 12.25%. The different behavior of the two interfacial layers can be ascribed to varying shunt resistance values, which are lower for polylysine, causing a reduction in indoor performance. This study highlights the importance of properly choosing the interfacial layer of the OSC depending on the desired application, paving the way toward OPV devices suitable for portable and wearable applications.