posted on 2016-03-21, 15:50authored byRobert
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.