Tailoring the Open-Circuit Voltage Deficit of Wide-Band-Gap Perovskite Solar Cells Using Alkyl Chain-Substituted Fullerene Derivatives.

Wide-band-gap (WB) perovskite devices are promising as the top cell of silicon-perovskite tandem devices to boost the efficiency beyond the Shockley-Queisser limit. Here, we tailor the performance parameters of WB mixed-halide perovskite solar cell with long alkyl chain-substituted fullerene derivatives as an electron transport layer (ETL). The device with C60-fused N-methylpyrrolidine- meta-dodecyl phenyl (C60MC12) demonstrates an enhanced power conversion efficiency of 16.74% with the record open circuit voltage ( VOC) of 1.24 V, an increase by 70 mV with concomitant VOC deficit reduction to 0.47 V. This is achieved by mitigating the recombination loss through the use of highly crystalline C60MC12 film compared to amorphous [6,6]-phenyl-C61-butyric acid methyl ester layer. The device analysis reveals the soothing of the defect activities with shallower defect states and passivation of the interface recombination centers for the device with C60MC12. We ascribe this property to the crystallinity of fullerene derivatives as ETL, which is also important for the optimization of device parameters, besides the band alignment matching of WB perovskite devices.