Why can electron-hole recombination reduce a solar cell's electrical output?

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Diagram of a solar cell showing labeled layers, including a front electrical contact grid, antireflection layer, absorber layer, back junction layer, and back electrical contact layer, with arrows indicating light entering and terminals connecting to a circuit. — solar cell A commonly used solar cell structure. In many such cells, the absorber layer and the back junction layer are both made of the same material.

In a solar cell, the generation of electric current relies on the movement of electrons and holes created when photons excite electrons from the valence band to the conduction band.1

Electron-hole recombination reduces a solar cell's electrical output because it removes these charge carriers before they can contribute to the current. When an electron and a hole recombine, they effectively cancel each other out, preventing the flow of electricity that would otherwise be induced by a voltage.1

This process is an intrinsic property of semiconductor materials, but it is further exacerbated by crystal defects—such as grain boundaries, impurities, and dislocations—as well as by surfaces and interfaces within the cell. Consequently, minimizing these recombination sites is a critical challenge in materials science to maintain a sizable current and improve the overall efficiency of photovoltaic systems.1