Thermodynamic reciprocity in scanning photocurrent maps

Scanning photocurrent maps in inhomogeneous materials contain nontrivial patterns, which often can only be understood with a full model of device geometry and nonuniformities. We remark on the consequences of Onsager reciprocity to the photocurrent in linear response, with immediate applications in photovoltaic and photothermoelectric effects. In particular with photothermoelectric effects, we find that the ampere-per-watt responsivity is exactly governed by Peltier-induced temperature shifts in the same device when time-reversed and voltage-biased. We show, with the example of graphene, that this principle aids in understanding and modelling of photocurrent maps.