V_xIn_(2-x)S₃ Intermediate Band Absorbers Deposited by Atomic Layer Deposition

Substitutional alloys of several thin film semiconductors have been proposed as intermediate band (IB) materials for use in next-generation photovoltaics, which aim to utilize a larger fraction of the solar spectrum without sacrificing significant photovoltage. We demonstrate a novel approach to IB material growth, namely atomic layer deposition (ALD), to allow unique control over substitutional-dopant location and density. Two new ALD processes for vanadium sulfide incorporation are introduced, one of which incorporates a vanadium(III) amidinate previously untested for ALD. Using this process, we synthesize the first thin film V_xIn_(2-x)S₃ intermediate band semiconductors and further demonstrate that the V:In ratio, and therefore intraband gap density of states, can be finely tuned according to the ALD dosing schedule. Deposition on a crystalline In₂S₃ underlayer promotes the growth of a tetragonal β-In₂S₃-like phase V_xIn_(2-x)S₃, which exhibits a distinct sub-band gap absorption peak with onset near 1.1 eV in agreement with computational predictions. However, the V_xIn_(2-x)S₃ films lack the lower-energy transition predicted for a partially filled IB, and photoelectrochemical devices reveal a photocurrent response only from illumination with energy sufficient to span the parent band gap.