Absorption Spectrum-Compensating Configuration Reduces the Energy Loss of Nonfullerene Organic Solar Cells

Using narrow bandgap nonfullerene acceptors (NFAs) can broaden the absorption spectrum of organic solar cells (OSCs) to the near-infrared region. However, the simultaneously decreased extinction coefficient of the active layer at the blue region results in inevitable light escaping and energy loss. Herein, a blazed grating-based device configuration consisting of a patterned rear electrode is employed to compensate for the low absorption of nonfullerene OSCs. Experimental results reveal that the normal incidence light, especially blue light, that bounces off the patterned rear electrode is concentrated in a large tilted angle and subsequently trapped in waveguide mode. Along with the excitation of surface plasmon polariton, the structured nonfullerene OSCs using a new-designed PM6:M36 active layer obtain the broadband absorption enhancement with 1.5 times increase at the blue region. The optimized device achieves an 8.95% increase in photocurrent and a champion power conversion efficiency of approaching 18%, which is the highest reported value among all the devices based on A-D-A type NFAs.