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Organic photovoltaic cell relying on energy transfer with over 20% efficiency in indoor lighting

Device optimization of a three-layer and fullerene-free organic photovoltaic device stack allowed us to achieve over 8% power conversion efficiency (PCE). Complementary small molecule absorbers enable a broad absorption up to 800 nm leading to short-circuit current density of 14.5 mA/cm2. Simultaneously an elevated open-circuit voltage of 1 V can be achieved as the third absorbers' contribution is harvested via exciton energy transfer. Under AM1.5G standard light conditions, the PV cell reaches a PCE of 8.4%. The simple structure, where three materials contribute in parallel to the photocurrent generation, motivated us to assess its performance in varying indoor lighting conditions, where it reaches a PCE of over 20% due to increase in responsivity and reduced series resistance.