Heterojunction photovoltaic cells

Abstract

A theoretical evaluation of a heterojunction photovoltaic cell is presented. Short circuit current densities, collection efficiencies, open circuit voltages, and maximum power outputs are calculated and compared to those of equivalent homojunction cells made of the two semiconductor materials forming the heterojunction. The analysis considers the abrupt p-n heterojunction and treats only the case of uniform illumination. Open circuit voltages and short circuit currents, as derived, cannot exceed the values obtained in the equivalent homojunction cells. Cell efficiencies for heterojunctions are thus bounded by the efficiencies of the corresponding homojunctions and any advantages of the cells are limited to those arising out of the window effect (low energy photons pass through one semiconductor to generate carriers in the junction region of the other): i.e., reduced surface recombination losses, and lower sheet resistances.