Angstrom Solar Center

Uppsala, Sweden

Angstrom Solar Center

Uppsala, Sweden
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Kosyak V.,Angstrom Solar Center | Postnikov A.V.,University of Lorraine | Scragg J.,Angstrom Solar Center | Scarpulla M.A.,University of Utah | Platzer-Bjorkman C.,Angstrom Solar Center
Journal of Applied Physics | Year: 2017

Herein, we study the native point defect equilibrium in Cu2ZnSnS4 (CZTS) by applying a statistical thermodynamic model. The stable chemical-potential space (SCPS) of CZTS at an elevated temperature was estimated directly, on the basis of deviations from stoichiometry calculated for the different combinations of chemical potential of the components. We show that the SCPS is narrow due to high concentration of VCu - ZnCu+ complex which is dominant over other complexes and isolated defects. The CZTS was found to have p-type conductivity for both stoichiometric and Cu-poor/Zn-rich composition. It is established that the reason for this is that the majority of donor-like ZnCu+ antisites are involved in the formation of VCu - ZnCu+ complex making CuZn- dominant and providing p-type conductivity even for Cu-poor/Zn-rich composition. However, our calculation reveals that the hole concentration is almost insensitive to the variation of the chemical composition within the composition region of the single-phase CZTS due to nearly constant concentration of dominant charged defects. The calculations for the full equilibrium and quenching indicate that hole concentration is strongly dependent on the annealing temperature and decreases substantially after the drastic cooling. This means that the precise control of annealing temperature and post-annealing cooling rate are critical for tuning the electrical properties of CZTS. © 2017 Author(s).


Scragg J.J.,Angstrom Solar Center | Dale P.J.,University of Luxembourg | Colombara D.,University of Bath | Peter L.M.,University of Bath
ChemPhysChem | Year: 2012

A simple and useful thermodynamic approach to the prediction of reactions taking place during thermal treatment of layers of multinary semiconductor compounds on different substrates has been developed. The method, which uses the extensive information for the possible binary compounds to assess the stability of multinary phases, is illustrated with the examples of Cu(In,Ga)Se 2 and Cu 2ZnSnSe 4 as well as other less-studied ternary and quaternary semiconductors that have the potential for use as absorbers in photovoltaic devices. © 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.


Ericson T.,Angstrom Solar Center | Scragg J.J.,Angstrom Solar Center | Hultqvist A.,Angstrom Solar Center | Hultqvist A.,Stanford University | And 4 more authors.
IEEE Journal of Photovoltaics | Year: 2014

To improve the conduction band alignment and explore the influence of the buffer-absorber interface, we here investigate an alternative buffer for Cu 2 ZnSnS4 (CZTS) solar cells. The Zn(O, S) system was chosen since the optimum conduction band alignment with CZTS is predicted to be achievable, by varying oxygen to sulfur ratio. Several sulfur to oxygen ratios were evaluated to find an appropriate conduction band offset. There is a clear trend in open-circuit voltage (Voc), with the highest values for the most sulfur rich buffer, before going to the blocking ZnS, whereas the fill factor peaks at a lower S content. The best alternative buffer cell in this series had an efficiency of 4.6% and the best CdS reference gave 7.3%. Extrapolating Voc values to 0 K gave activation energies well below the expected bandgap of 1.5 eV for CZTS, which indicate that recombination at the interface is dominating. However, it is clear that the values are affected by the change of buffer composition and that increasing sulfur content of the Zn(O, S) increases the activation energy for recombination. A series with varying CdS buffer thickness showed the expected behavior for short wavelengths in quantum efficiency measurements but the final variation in efficiency was small. © 2013 IEEE.


PubMed | Angstrom Solar Center
Type: Journal Article | Journal: Chemphyschem : a European journal of chemical physics and physical chemistry | Year: 2012

A simple and useful thermodynamic approach to the prediction of reactions taking place during thermal treatment of layers of multinary semiconductor compounds on different substrates has been developed. The method, which uses the extensive information for the possible binary compounds to assess the stability of multinary phases, is illustrated with the examples of Cu(In,Ga)Se(2) and Cu(2)ZnSnSe(4) as well as other less-studied ternary and quaternary semiconductors that have the potential for use as absorbers in photovoltaic devices.

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