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Title CuSb(S,Se)₂ thin film heterojunction photovoltaic devices
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Publication Date
Date Accessioned
Degree PhD
Discipline/Department Chemical and Biological Engineering
Degree Level doctoral
University/Publisher Colorado School of Mines
Abstract Thin film heterojunction solar cells based on CuSb(S,Se)2 absorbers are investigated for two primary reasons. First, antimony is more abundant and less expensive than elements used in current thin film photovoltaics, In, Ga, and Te, and so, successful integration of Sb based materials offers greater diversification and scalability of solar energy. Second, the CuSb(S,Se)2 ternary is chemically, electronically, and optically similar to the well-known, high efficiency, CuIn(S,Se)2 based materials. It is therefore postulated that the copper antimony ternaries will have similar defect tolerant electronic transport that may allow for similar highly efficient photoconversion. However, CuSb(S,Se)2 forms a layered crystal structure, different from the tetrahedral coordination found in conventional solar absorbers, due to the non-bonding lone pair of electrons on the antimony site. Thus examination of 2D antimony ternaries will lend insight into the role of structure in photoconversion processes. To address these questions, the semiconductors of interest (CuSbS2 & CuSbSe2) were first synthesized on glass by combinatorial methods, to more quickly optimize process condi- tions. Radio-frequency (RF) magnetron co-sputtering from Sb2(S,Se)3 and Cu2(S,Se) targets were used, without rotation, to produce chemical and flux graded libraries which were then subjected to high throughput characterization of structure (XRD), composition (XRF), con- ductivity (4pp), and optical absorption (UV/Vis/NIR). This approach rapidly identified processes that generated phase pure material with tunable carrier concentration by apply- ing excess Sb2(S,Se)3 within a temperature window bound by the volatility of Sb2(S,Se)3 and stability of the ternary phase. The resulting phase pure thin films were then incor- porated into the traditional CuInGaSe2 (CIGS) substrate photovoltaic (PV) architecture, and the resulting device performance was correlated to gradients in composition, sputter flux, absorber thickness, and grain orientation. This combinatorial work was complimented by individual measurements of photoluminescence (PL), capacitance-voltage (CV), external quantum efficiency (EQE), terahertz (THz) spectroscopy, and photoelectrochemical (PEC) measurements. CuSbS2-based libraries produced devices with just 1% power conversion efficiency, mainly limited by high levels of recombination associated with high density of shallow trap states. Conversely, the selenide variant showed more promise, with initial cells producing signifi- cantly more photocurrent, nearly 60% of the theoretical maximum, and likewise 5% efficient devices, mainly due to fewer trap states. However, the selenide is still limited by short carrier diffusion lengths, therefore demonstrating that structure does seem to play limiting role in photoconversion processes. Overall, the CuSb(S,Se)2 material system is only likely to merit further exploration if it can be incorporated into an alternate device structure less dependent on collection by diffusion. There is a small possibility that…
Subjects/Keywords chalcostibite; electrical properties; photovoltaics; semiconductor; thin flm; vacuum deposition
Contributors Wolden, Colin Andrew (advisor); Zakutayev, Andriy (committee member); O'Hayre, Ryan P. (committee member); Zimmerman, Jeramy D. (committee member); Gorman, Brian P. (committee member)
Language en
Rights Copyright of the original work is retained by the author.
Record ID handle:11124/166675
Repository colo-mines
Date Retrieved
Date Indexed 2018-10-24
Grantor Colorado School of Mines
Note [] 2015 Fall; [] Includes illustrations (some color); [] Includes bibliographical references.;

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