Unique Curve for the Radiative Photovoltage Deficit Caused by the Urbach Tail

The photovoltage V-oc of high-performance solar cells such as GaAs and metal halide perovskites is affected by the exponential Urbach tail in the absorption spectrum, with an energy parameter E-U. It has been observed that increasing Urbach energy decreases the maximum photovoltage that can be achieved. On the basis of detailed balance and reciprocity of absorption and emission, we present a calculation that shows that the voltage loss due to the exponential tail in an absorption obeys a universal relation Delta V-oc(rad) = (k(B)T/q) ln(1 - E-U/k(B)T) for E-U < k(B)T, independently of the bandgap.

Automated summary

The photovoltage of high-performance solar cells like GaAs and metal halide perovskites is affected by the exponential Urbach tail in the absorption spectrum, with a parameter E-U. Increasing Urbach energy leads to a decrease in the maximum achievable photovoltage. A calculation based on the detailed balance and reciprocity of absorption and emission shows that the voltage loss due to the exponential tail in absorption follows a universal relation.