Optically thin light-absorbers for increasing photochemical energy-conversion efficiencies

Abstract

Photochemical energy conversion is more efficient when a single light-absorbing unit is split into multiple light-absorbing units (N) that are each 1/N as thick as the single light-absorbing unit and thus use the same amount of material as the single light-absorbing unit. For electrocatalytic parameters relevant to water electrolysis, the maximum efficiency for solar-to-fuel conversion from a 1.75 eV bandgap material increases from approximately 1% for a single light-absorbing unit to greater than 20% for 128 identical stacked light-absorbing units. Alterations in utilization of photons results in a better match of the light-absorber power output to the load of the chemical transformation and in the case of high-quality light-absorbers there is an added benefit from radiative coupling between the light-absorbing units via photon recycling.