No abstract

Secondary phases like Cu2SnS3 are major obstacles for kesterite thin film solar cell applications. We prepare Cu2SnS3 using identical annealing conditions as used for the kesterite films. By x-ray diffraction, the crystal structure of Cu2SnS3 was identified as monoclinic. Polarization-dependent Raman investigations allowed the identification of the dominant peaks at 290 cm−1 and 352 cm−1 with the main A′ symmetry vibrational modes from the monoclinic Cu2SnS3 phase. Furthermore, micro-resolved Raman investigations revealed local variations in the spectra that are attributed to a secondary phase (possibly Cu2Sn3S7). This exemplifies the abilities of micro-resolved Raman measurements in the detection of secondary phases.

Alongside with Cu 2 ZnSnS 4 and SnS, the p-type semiconductor Cu 2 SnS 3 also consists of only Earth abundant and low-cost elements and shows comparable opto-electronic properties, with respect to Cu 2 ZnSnS 4 and SnS, making it a promising candidate for photovoltaic applications of the future. In this work, the ternary compound has been produced via the annealing of an electrodeposited precursor in a sulfur and tin sulfide environment. The obtained absorber layer has been structurally investigated by X-ray diffraction and results indicate the crystal structure to be monoclinic. Its optical properties have been measured via photoluminescence, where an asymmetric peak at 0.95 eV has been found. The evaluation of the photoluminescence spectrum indicates a band gap of 0.93 eV which agrees well with the results from the external quantum efficiency. Furthermore, this semiconductor layer has been processed into a photovoltaic device with a power conversion efficiency of 0.54 %, a short circuit current of 17.1 mA/cm 2 , a open circuit voltage of 104 mV hampered by a small shunt resistance, a fill factor of 30.4 %, and a maximal external quantum efficiency of just less than 60 %. In addition, the potential of this Cu 2 SnS 3 absorber layer for photovoltaic applications is discussed.

The degradation of CuInSe2 absorbers in ambient air is observed by the decay of the quasi-Fermi level splitting under well defined illumination with time. The decay is faster and stronger in absorbers with [Cu]/[In]<1 than in ones with a higher ratio. It can be attributed to the oxidation of the sample. Epitaxial films containing no Na show very similar trends, indicating that decay and oxidation are independent of the Na content. A standard CdS layer commonly used as buffer in solar cells, terminates the decay even over many months. Aged absorbers can be completely restored by a KCN etch.

Kesterite is an attractive material for absorber layers in thin film photovoltaics. Solar cells based on kesterite have shown a substantial progress over the last decade; nevertheless, further improvements in device efficiency are pending due to the open‐circuit voltage (Voc) deficit (i.e., difference between the maximum V oc that can be achieved according to Shockley–Queisser limit and actual V oc from the device). In this study, the optoelectronic properties of the author's internal record Cu2ZnSnSe4 solar cell, which shows a power conversion efficiency of 11.4%, are presented. The device measurements reveal a Voc deficit of 337 mV, which is one of the lowest V oc deficits in the literature. Moreover, an unusual behavior for kesterite is observed: (i) photon energy of the photoluminescence emission and (ii) the extrapolated V oc for 0 K are both matching the band gap region of the absorber. These results indicate a significant improvement in the recombination characteristics and absorber quality in comparison to other kesterite devices in literature.