The combination of oxide and heavier chalcogenide layers
in thin film photovoltaics suffers limitations associated with oxygen
incorporation and sulfur deficiency in the chalcogenide layer or with
a chemical incompatibility which results in dewetting issues and defect
states at the interface. Here, we establish atomic layer deposition
(ALD) as a tool to overcome these limitations. ALD allows one to obtain
highly pure Sb2S3 light absorber layers, and
we exploit this technique to generate an additional interfacial layer
consisting of 1.5 nm ZnS. This ultrathin layer simultaneously resolves
dewetting and passivates defect states at the interface. We demonstrate
via transient absorption spectroscopy that interfacial electron recombination
is one order of magnitude slower at the ZnS-engineered interface than
hole recombination at the Sb2S3/P3HT interface.
The comparison of solar cells with and without oxide incorporation
in Sb2S3, with and without the ultrathin ZnS
interlayer, and with systematically varied Sb2S3 thickness provides a complete picture of the physical processes
at work in the devices.
We prepare arrays of cylindrical pores featuring large periods (460 nm and 600 nm) by anodization of aluminum. A self-ordered monolayer of nanospheres drives the subsequent pore ordering and yields a quality of order significantly improved with respect to the traditional two-step anodization procedure.
Antimony chalcogenides
represent a family of materials of low toxicity
and relative abundance, with a high potential for future sustainable
solar energy conversion technology. However, solar cells based on
antimony chalcogenides present open-circuit voltage losses that limit
their efficiencies. These losses are attributed to several recombination
mechanisms, with interfacial recombination being considered as one
of the dominant processes. In this work, we exploit atomic layer deposition
(ALD) to grow a series of ultrathin ZnS interfacial layers at the
TiO
2
/Sb
2
S
3
interface to mitigate
interfacial recombination and to increase the carrier lifetime. ALD
allows for very accurate control over the ZnS interlayer thickness
on the ångström scale (0–1.5 nm) and to
deposit highly pure Sb
2
S
3
. Our systematic study
of the photovoltaic and optoelectronic properties of these devices
by impedance spectroscopy and transient absorption concludes that
the optimum ZnS interlayer thickness of 1.0 nm achieves the
best balance between the beneficial effect of an increased recombination
resistance at the interface and the deleterious barrier behavior of
the wide-bandgap semiconductor ZnS. This optimization allows us to
reach an overall power conversion efficiency of 5.09% in planar configuration.
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