A 1 cm2 Organic Solar Cell with 15.2% Certified Efficiency. Detailed Characterization and Identification of Optimization Potential
In organic photovoltaics, high power conversion efficiencies (PCE) are mostly achieved on device areas well below 0.1 cm2. Herein, organic solar cells based on a D18:Y6 absorber layer on an active area of > 1 cm2 with a certified PCE of 15.24% are reported. The impacts of the sheet resistance of the transparent electrode and the cell design are quantified by means of full optical device simulations and an analytical electrical model. Three imaging methods (light beam-induced current, dark lock-in thermography, and electroluminescence [EL]) are applied and reveal a strong homogeneity of the record cell. Nevertheless, it is found that there is substantial room for improvement mostly in current but also in fill factor and that a PCE of 18.6% on >1 cm2 is feasible with this absorber material. Further, photoluminescence (PL) and EL spectroscopy reveal that both emissions occur at the same wavelength(s) and are very similar to the PL spectrum of a pure Y6 acceptor film. The latter points strongly toward electronic coupling between the S1 states of the acceptor and the charge transfer states at the donor/acceptor interface.