arXiv subjects

Andriy Zakutayev

Publications and source records attributed to Andriy Zakutayev.

76 records · Page 5Linked to original sources

arXiv2015

CuSbSe2 photovoltaic devices with 3% efficiency

Recent technical and commercial successes of existing thin film solar cell technologies motivates exploration of next-generation photovoltaic (PV) absorber materials. Of particular scientific interest are compounds like CuSbSe$_2$, which do not have the conventional tetrahedral semiconductor bonding. Here, we demonstrate 1.5 μm thick CuSbSe$_2$ PV prototypes prepared at 380-410°C by a self-regulated sputtering process using the conventional substrate device architecture. The p-type CuSbSe$_2$ absorber has a 1.1 eV optical absorption onset, ~$10^{5}$ cm$^{-1}$ absorption coefficient at 0.3 eV above the onset, and a hole concentration of ~10$^{17}$ cm$^{-3}$. The promising >3% energy conversion efficiency (Jsc = 20 mA/cm$^2$, FF = 0.44, Voc = 0.35 V) in these initial devices is limited by bulk recombination that limits photocurrent, device engineering issues that affect fill factor, and a photovoltage deficit that likely results from the non-ideal CuSbSe2/CdS band offset.

cond-mat.mtrl-sci↗

arXiv2015

Accelerated development of CuSbS2 thin film photovoltaic device prototypes

Development of alternative thin film photovoltaic technologies is an important research topic due to the potential for low-cost, large-scale fabrication of high-efficiency solar cells. Despite the large number of promising alternative absorbers and corresponding contacts, the rate of progress is limited by complications that arise during solar cell fabrication. One potential solution to this problem is the high-throughput combinatorial method, which has been extensively used for research and development of individual absorber and contact materials. Here, we demonstrate an accelerated approach to development of thin film photovoltaic device prototypes based on the novel CuSbS2 absorber, using the device architecture employed for CuInxGa(1-x)Se2 (CIGS). The newly developed three-stage, self-regulated CuSbS2 growth process enables the study of PV device performance trends as a function of phase purity, crystallographic orientation, layer thickness of the absorber, and numerous back contacts. This exploration results in initial CuSbS2 device prototypes with ~1% conversion efficiency; currently limited by low short-circuit current due to poor collection of photoexcited electrons, and a small open-circuit voltage due to a cliff-type conduction band offset at the CuSbS2/CdS interface (suggested by first-principles calculations). Overall, these results illustrate the potential of combinatorial methods to accelerate the development of thin film photovoltaic devices with novel absorbers.

cond-mat.mtrl-sci↗

arXiv2015

Effects of disorder on carrier transport in Cu$_2$SnS$_3$

In recent years, further improvements in the efficiency of Cu$_2$ZnSn(S,Se)$_4$ photovoltaic devices have been hampered due to several materials issues, including cation disorder. Cu$_2$SnS$_3$ is a promising new absorber material that has attracted significant interest in recent years. However, similar to CZTS, Cu$_2$SnS$_3$ displays cation disorder. In this work, we develop synthetic techniques to control the disorder in Cu$_2$SnS$_3$ thin films. By manipulating the disorder in this material, we observe crystal structure changes and detect improvements in the majority carrier (hole) transport. However, when the minority carrier (electron) transport was investigated using optical pump terahertz probe spectroscopy, minimal differences were observed between the ordered and disordered Cu$_2$SnS$_3$. By combining these results with first-principles and Monte Carlo theoretical calculations, we are able to conclude that even ostensibly "ordered" Cu$_2$SnS$_3$ displays minority carrier transport properties corresponding to the disordered structure. The presence of extended planar defects in all samples, observed in TEM imaging, suggests that disorder is present even when it is not detectable using traditional structural characterization methods. The results of this study highlight some of the challenges to the further improvement of Cu$_2$SnS$_3$-based photovoltaics, and have implications for other disordered multinary semiconductors such as CZTS.

cond-mat.mtrl-sci↗

arXiv2014

Electronic band structure and ambipolar electrical properties of Cu2O based semiconductor alloys

Tuning the opto-electronic properties through alloying is essential for semiconductor technology. Currently, mostly isovalent and isostructural alloys are used (e.g., group-IV and III-V), but a vast and unexplored space of novel functional materials is conceivable when considering more complex alloys by mixing aliovalent and heterostructural constituents. The real challenge lies in the quantitative property prediction for such complex alloys to guide their experimental exploration. We developed an approach to predict compositional dependence of both band-structure and electrical properties from ab-initio calculations by extending conventional dilute defect model to higher (alloy) concentrations. Considering alloying of aliovalent (Mg, Zn, Cd) cations and isovalent anions (S, Se) into Cu2O, we predict tunability of band-gap energies and doping levels over a wide range, including the type conversion from p- to n-type. Initial synthesis and characterization of Zn and Se substituted Cu2O support the defect model, suggesting these alloys as promising novel oxide semiconductor materials.

cond-mat.mtrl-sci↗