Engineering middle transparent electrodes for enhanced performance of parallel tandem organic photovoltaics

Organic Photovoltaics (OPVs) have emerged as leading materials for next-generation energy sources. Despite the advancements in organic photoactive materials, research on parallel tandem organic photovoltaics (PT-OPVs) has been limited. The efficiency of PT-OPVs can be improved by reducing the difference in the open-circuit voltages (VOC) between the front and back subcells. However, there is a significant gap in research on the middle transparent electrode (MTE), which is crucial for achieving the desired energy-level alignment between the photoactive layers of these subcells and establishing electrical connectivity between them. This gap limits the utilization of reported high-performance photoactive materials in PT-OPV devices. To address this issue, a novel MTE is developed by depositing a copper (I) thiocyanate (CuSCN) hole transport layer on a molybdenum oxide/ thin silver/molybdenum oxide (MAM) multilayer structure. The MAM/CuSCN MTE is distinguished by its higher work function and reduced surface roughness. As a result, integrating the MAM/CuSCN MTE in the PT-OPVs substantially increases the VOC of the back subcells (from 714 mV to 773 mV) while simultaneously minimizing the difference in VOC between the front and back subcells; thus, improving the performance of the device. Our findings provide valuable insights into the engineering of MTEs to enhance PT-OPVs' efficiency.