American Chemical Society
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VxIn(2–x)S3 Intermediate Band Absorbers Deposited by Atomic Layer Deposition

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journal contribution
posted on 2016-03-21, 15:50 authored by Robert F. McCarthy, Matthew S. Weimer, Richard T. Haasch, Richard D. Schaller, Adam S. Hock, Alex B. F. Martinson
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 VxIn(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 VxIn(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 VxIn(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.