Environmentally sustainable fabrication of organic solar cells: preserving the power conversion efficiency while reducing the material footprint†

Abstract

Organic solar cells (OSCs) have attracted significant interest due to their utilization of a solution-based approach, which allows for easier fabrication procedures. In recent years, OSCs have successfully reached more than 19.0% of power conversion efficiency (PCE). Most of these interesting developments commonly utilized halogenated solvents such as chlorobenzene (CB), chloroform (CF), 1,2-dichlorobenzene (ODCB), etc. These halogenated solvents are harmful to human health as well as the environment. Therefore, the utilization of harmful solvents limits its capability as an environmentally friendly technology. With an aim to employ eco-friendly solvents for OSC fabrication, we present our research on the fabrication of PTB7-Th:PC₇₁BM-based organic solar cells (OSCs) using a combination of non-halogenated and relatively eco-friendly solvents. The combination of 2-methylanisole (MA) and mesitylene (MY) in a specific ratio (7 : 3) has been identified as a suitable substitute solvent. By employing these solvents, we were able to reach a maximum PCE of 7.32% for the OSCs with an inverted device architecture ITO/ZnO/PTB7-Th:PC₇₁BM/MoO_x/Ag, which is comparable to the PCE of OSCs processed using ODCB solvent. Furthermore, we established the universality of a relatively non-toxic solvent combination (MA : MY) for eco-friendly OSCs by achieving a PCE of 11.05% for the ternary device architecture ITO/ZnO/PTB7-Th:Y7:IT-M/MoO_x/Ag.