(262c) Evaluating Novel Semiconducting Materials for Photovoltaic Applications: A Case Study of Copper Arsenic Sulfide (Cu3AsS4)

Evaluating
Novel Semiconducting Materials for Photovoltaic Applications: A Case Study of
Copper Arsenic Sulfide (Cu₃AsS₄)

Scott
A. McClary,¹ Weiwei Meng,² Xinxing Yin,²
Joseph Andler,³ Siming Li,⁴ Louis R. Schroeder,¹
Jason B. Baxter,⁴ Carol A. Handwerker,³ Yanfa Yan,²
and Rakesh Agrawal¹

1
– Davidson School of Chemical Engineering, Purdue University, West Lafayette IN

2
– Department of Physics and Astronomy, University of Toledo, Toledo OH

3
– Department of Materials Engineering, Purdue University, West Lafayette, IN

4
– Department of Chemical and Biological Engineering, Drexel University,
Philadelphia, PA

The
ubiquity of solar radiation makes it a prime candidate to satisfy the world’s
energy demand for the foreseeable future. Thin-film solar cells (TFSCs), which
convert sunlight directly into electricity, are widely researched because of
their high efficiencies, ability to be fabricated on flexible substrates, and
amenability to solution-phase deposition (and hence scalable manufacturing
techniques). The current TFSC market is dominated by cadmium telluride (CdTe)
and copper indium gallium diselenide (CIGSe). However, the low earth abundance
of elements In and Te cast significant doubt on the ability of such materials
to comprise a significant portion of the world’s future energy portfolio.
Copper zinc tin sulfoselenide (CZTSSe) is another well-researched material for
TFSCs, but inherent defects and potential fluctuations make the achievement of
high efficiencies difficult, if not impossible. To ensure the broad impact of
future TFSCs, new materials must satisfy numerous criteria, including
constituent earth abundant elements, stability, low concentrations of harmful
defects, and ideal optoelectronic properties for solar energy conversion.

One
emerging TFSC material is copper arsenic sulfide, Cu₃AsS₄. 
Density functional theory (DFT) calculations have estimated bandgaps in the
ideal range for solar energy conversion (1.2 – 1.4 eV), absorption coefficients
exceeding 10⁵ cm^-1 in the visible range, and solar
conversion efficiencies exceeding 25%.^1,2
Additionally, Cu₃AsS₄ consists of three earth abundant
elements with dissimilar cation sizes and charge states, greatly reducing the
likelihood of antisite defects seen in CZTSSe. Experimentally, a strong photocurrent
and ideal band gap have been demonstrated in natural minerals³
and synthetic nanoparticles.^4,5
Recently, our group developed the first method to synthesize thin films of Cu₃AsS₄.⁶ By
heating nanoparticles in an As₂S₅ atmosphere, thin films
with micron-sized dense grains are formed; we attribute the grain growth to the
presence of a liquid phase consisting primarily of arsenic and sulfur. 
Preliminary solar cells were fabricated using these thin films as the absorber
layer, and a champion device efficiency of 0.35% has been achieved.⁷

While
the initial results are promising, the long-term feasibility of Cu₃AsS₄
as a TFSC material must be explored before significant research efforts are
expended. In this talk, we present detailed optoelectronic and materials
characterization of Cu₃AsS₄ thin films. We demonstrate
that Cu₃AsS₄ has suitable optoelectronic properties (e.g.
absorption coefficients, carrier lifetimes, etc.) and low harmful defect
concentrations, both of which are necessary for high-efficiency TFSCs. With our
results suggesting that Cu₃AsS₄ is worthy of continued exploration,
we progress towards film improvement and device optimization, using alternative
film deposition techniques and buffer layers. Our results motivate further
research and development of Cu₃AsS₄-based solar cells,
and we expect that our methods can be adapted to development of other novel TFSC
materials.

References

(1)      Yu, L.;
Kokenyesi, R. S.; Keszler, D. A.; Zunger, A. Inverse Design of High Absorption
Thin-Film Photovoltaic Materials. Adv. Energy Mater. 2013, 3
(1), 43–48.

(2)
     Shi, T.; Yin, W.-J.; Al-Jassim, M.; Yan, Y. Structural, Electronic, and
Optical Properties of Cu₃-V-VI₄ Compound Semiconductors. Appl.
Phys. Lett. 2013, 103 (15), 152105.

(3)
     Pauporté, T.; Lincot, D. Electrical, Optical and Photoelectrochemical
Properties of Natural Enargite, Cu₃AsS₄. Adv. Mater.
Opt. Electron. 1995, 5 (6), 289–298.

(4)
     Balow, R. B.; Sheets, E. J.; Abu-Omar, M. M.; Agrawal, R. Synthesis and
Characterization of Copper Arsenic Sulfide Nanocrystals from Earth Abundant
Elements for Solar Energy Conversion. Chem. Mater. 2015, 27
(7), 2290–2293.

(5)
     Balow, R. B.; Miskin, C. K.; Abu-Omar, M. M.; Agrawal, R. Synthesis and
Characterization of Cu₃(Sb_1–xAs_x)S₄
Semiconducting Nanocrystal Alloys with Tunable Properties for Optoelectronic
Device Applications. Chem. Mater. 2017, 29 (2), 573–578.

(6)
     McClary, S. A.; Andler, J.; Handwerker, C. A.; Agrawal, R.
Solution-Processed Copper Arsenic Sulfide Thin Films for Photovoltaic
Applications. J. Mater. Chem. C 2017, 5 (28), 6913–6916.

(7)
     McClary, S. A.; Andler, J.; Handwerker, C. A.; Agrawal, R. Fabrication of
Copper Arsenic Sulfide Thin Films from Nanoparticles for Application in Solar
Cells. In 44th IEEE Photovoltaics Specialists Conference; 2017.