Fig. 1: Molecular structure and photovoltaic performance of single-junction devices.

a Chemical structures, b thin film absorption coefficients, and c UPS results of PM6 (red line), PM7 (yellow line), and Y6 (blue line). Fermi energy was determined by linear extrapolating the high binding energy portion of the spectrum, and HOMO energy level was referred to low binding energy onset. d Energy level alignment and double cascading transport pathways for quaternary system. e Current density–voltage characteristics and f histogram of PCE measurement for 40 devices on binary, ternary, and quaternary devices under constant incident light intensity (AM 1.5 G, 100 mW cm⁻²). g Normalized PCE, V_OC, J_SC, and FF (20 devices statistics) against aging time under illumination equivalent to ~1 sun for 1000 h (red for binary and blue for quaternary, the error bar is from the deviation of twenty samples).