is the most used back contact in Cu 2 ZnSn(S 1-x Se x ) 4 based solar cells. However, it has been suggested recently that Mo is not stable at the interface with Cu 2 ZnSn(S 1-x Se x ) 4 . In addition, to the best of our knowledge, no experimental study has been carried out so far to test whether solar cells built on another back contact could exhibit better photovoltaic properties. For this purpose, various metals (Au, W, Pd, Pt, and Ni) are deposited on top of Mo, and it is demonstrated that it is possible to synthesize device-quality Cu 2 ZnSn(S 1-x Se x ) 4 thin films on W, Au, and Pt back contacts. It is shown that that W and Au back contacts allow enhancing the photogenerated current, but that Mo remains the best back contact in terms of power conversion efficiency. V

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This work deals with the influence of sodium on the properties of CZTSSe material and solar cells. For that purpose, two types of substrates are compared, one with low sodium content (borosilicate glass), the other one with higher sodium content (soda-lime glass). In each case the Na-content in the CZTSSe passing from the substrate through the Mo back contact is quantified by secondary ion mass spectroscopy analysis. Photoluminescence spectroscopy indicates that better quality material is achievable when increasing the Na-content in the CZTSSe. The material characterization results are compared to the photovoltaic properties.

A series of polycrystalline 1 μm thick SnO2 films were deposited onto borosilicate glass substrates by atmospheric pressure chemical vapor deposition. Unintentionally doped as-grown SnO2 layers had electron concentrations and mobility of 2–4×1017cm−3 and 25–30cm2∕Vs, respectively. Potential barriers and trap concentrations were calculated to be 30 meV and 2.3×1012cm−2, respectively. Upon N2∕vacuum annealing at 670 K for 15–20 min, the potential barrier height decreased to 8 meV and the electron mobility increased to 58cm2∕Vs. When doped with ammonia, the mobility of as-grown samples decreased to 0.5cm2∕Vs. The magnitude of the potential barriers varied, with ammonia doping, from 175 to 31 meV with trap densities of 4.7–1.2×1012cm−3, respectively. Upon vacuum∕N2 annealing at 670 K for 20 min, the electron mobilities of ammonia doped films recovered to 50–71cm2∕Vs, whereas the height of the potential barriers decreased to 3–4 meV with trap concentrations of 8–9×1011cm−2. The observed changes in the electrical properties are well described by a double back-to-back Schottky barrier model.