Cu2Zn1–x Cdx Sn(Se1–y Sy)4 monograin powders with different x ‐ and y ‐values were prepared from binary compounds in the liquid phase of flux material (KI) in evacuated quartz ampoules. All the materials had uniform composition and p‐type conductivity. PL spectra (10 K) of the as grown Cu2Zn1–x Cdx Sn(Se)4 monograin powders showed one PL band with peak position around 0.85 eV which shifted linearly to the lower energy side with increasing Cd content. Cu2ZnSnS4 material showed asymmetrical PL band at 1.31 eV attributed to band‐to‐tail recombination. RT Raman spectra of Cu2ZnSnSe4 revealed two main peaks at 196 cm–1 and 173 cm–1 and a third less intensive peak with varying peak position in the region 231–253 cm–1. Raman spectra of Cu2ZnSnS4 showed an intensive peak at 338 cm–1 and additional peaks at 287 cm–1 and 368 cm–1. Narrow sieved fractions of grown powders were used as absorber materials in monograin layer (MGL) solar cell structures: graphite/ Cu2Zn1–x Cdx Sn(Se1–y Sy)4/CdS/ZnO. The best so far solar cell that was based on the Cu2Zn0.8Cd0.2SnSe4 had open circuit voltage 422 mV, short circuit current 12 mA/cm2 and fill factor 44%. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

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Photoluminescence (PL) measurements of (x \ 0.5) single CuIn 1~x Ga x Se 2 crystals grown by the vertical Bridgmann technique were made at temperatures ranging from 11 K to 200 K and with various excitation powers. At low temperatures only one asymmetric PL band (BT-band) is present at 1.23 eV. It has a steeper decline on the high-energy side and nearly temperature independent low-energy side. At higher temperatures (T [ 140 K) the BB-band becomes visible at 1.31 eV. We used an asymmetric double sigmoidal function to Ðt the experimental PL spectra. The results of this Ðtting can be interpreted to show the presence of spatial potential Ñuctuations in our samples. Observed dependencies would seem to reveal that the BT band is indeed connected with the recombination of a free electron with a localized hole. It is shown that these relatively deep localized states are probably formed due to potential Ñuctuations in highly compensated material and are not connected with any particular acceptor defect. We show that this model conforms to most of the discovered dependencies.

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In this study, we investigated the photoluminescence (PL) properties of Cu2ZnSnS4 polycrystals. Two PL bands at 1.27 eV and 1.35 eV at T = 10 K were detected. Similar behaviour with temperature and excitation power was found for both PL bands and attributed to the band-to-impurity recombination. Interestingly, the thermal activation energies determined from the temperature dependence of the PL bands coincide. With the support of the Raman results, we propose that the observed PL bands arise from the band-to-impurity-recombination process involving the same deep acceptor defect with ionization energy of around 280 meV but different Cu2ZnSnS4 phase with different bandgap energy.