20.4% Power conversion efficiency from albedo-collecting organic solar cells under 0.2 albedo.

Highly efficient bifacial organic solar cells (OSCs) have not been reported due to limited thickness of the active layer in conventional configurations, not allowing for efficient harvesting of front sunlight and albedo light. Here, bifacial OSCs are reported with efficiency higher than the monofacial counterparts. The incorporation of pyramid-based asymmetrical optical transmission (AOT) array to a transparent silver electrode suppresses the escaping of front sunlight without sacrificing the harvesting of albedo light. Parasitic absorption induced by the excitation of surface plasmons in an AOT electrode is further reduced by doping organic emitter in electron transport layer and capping high dielectric constant film to silver. The rear electrode achieves a front transmittance of 7% and a rear transmission of 86%. At a conventional albedo of 0.2, the synergistic effect of AOT and minimized optical loss endow the bifacial OSCs with power conversion efficiency of 20.4%. This work paves the way for the utilization of albedo light in OSCs.