In any photovoltaic device, efficient energy conversion results from a competition between light harvesting, charge separation and transport, and charge recombination. Devices based on disordered materials such as solution processed molecular, inorganic and hybrid semiconductors, despite showing impressive advances in performance recently, typically show greater recombination losses than traditional crystalline semiconductor devices. The impact of non-radiative recombination on open-circuit voltage can be quantified precisely using luminescence techniques, but the method does not indicate the microscopic origin of the recombination nor its impact on overall solar cell performance. In this work, we use a variety of complementary experimental techniques and simulation to correlate the measured voltage losses to the underlying recombination mechanism in different types of solar cell including organic heterojunctions, lead halide perovskites and solution processed inorganic devices. We will focus on the impact of structural and energetic disorder, selectivity of contacts, density and energy of defect states and the competition of charge separation with recombination. We will comment on the extent to which disorder controls the losses to recombination, and address the question of whether large recombination losses are unavoidable in molecular materials.
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