a, EQE spectra of champion control and CF3-PA mixed Pb-Sn solar cells. The EQE values of CF3-PA device are substantially higher than those of previous works at wavelengths above 800 nm, mainly due to the use of thicker absorber while maintaining sufficient carrier transport. It is noted that such a high Jsc value is obtained herein together with high Voc and FF even when using a 1,200 nm absorber. b, Reverse and forward J-V curves of the champion CF3-PA mixed Pb-Sn solar cell. c, The steady-state PCE of the champion CF3-PA device.