The contribution of electron and hole conductivity to the transport loss in organic solar cells

The effective conductivity determines the reciprocal of the transport resistance, the dominant loss of fill factor in organic solar cells. We experimentally determine the dependence of effective conductivity on its electron and hole contributions. Using PM6:Y12 blends with tunable morphological and energetic disorder, we show that the effective conductivity follows a harmonic mean of electron and hole conductivities even across nearly three orders of magnitude in conductivity imbalance. We also validate the method for directly extracting effective conductivity from current-voltage measurements, eliminating the need to rely on indirect mobility and charge carrier density-based proxies. Our findings challenge the widespread use of geometric mean approximations and offer a more accurate framework for analysing and modelling transport in disordered organic semiconductors.