• Energy Research

Abstract The doping of Mg and Ga into ZnO is a method for obtaining excellent optical and electrical properties for a window layer in an inorganic solar cell. Because a tradeoff exists between the electrical and optical properties in the window layer, balancing them is important for enhancing the performance of the solar cells. From this viewpoint, the thickness change of the window layer affects the transmittance and the conductivity. In particular, it affects the transmittance in the NIR-IR region significantly, which can enhance the current collection but lead to poor conductivity when the transmittance of the window layer is increased. We examine the thickness effect of MGZO films for CZTSSe solar cells in order to determine the optimal conversion efficiency. The enhanced transmittance in the NIR-IR region with a thin MGZO layer contributed to a high current density, although the electrical resistivity was relatively high. An enhanced conversion efficiency of 7.54% was eventually recorded for an optimal thickness of the MGZO layer with an improved current density over 7 mA/cm2.

Abstract Cu2Sn(SxSe1−x)3 (CTSSe) (0 ≤ x ≤ 0.03) thin films are prepared using sputtered metal precursors. The influence of the quantity of selenium doped during an annealing process on the properties of CTSSe thin films and solar cells is investigated. The synthesized CTSSe thin films are grown in the monoclinic crystal structure with a densely packed morphology. The growth of the CTSSe thin films is successfully demonstrated by Raman spectroscopy and X-ray photoelectron spectroscopy (XPS) analyses. The band gap energy of the CTSSe thin films are extrapolated from the optical spectra of the band edge region to be 0.86 eV and 0.88 eV. A compositional analysis using X-ray fluorescence (XRF) spectroscopy shows a consistent increase in the selenium content with increase in the quantity of added selenium. This dependence is confirmed by changes in the crystallinity, composition, optical and electrical properties. CTSSe thin-film solar cells (TFSCs) were fabricated with a structure of Mo/CTSSe/CdS/i-ZnO/AZO/Al. The best efficiency of 2.49% was achieved for the fabricated CTSSe TFSC with a Voc of 190.8 mV, Jsc of 34.6 mA/cm2, and FF of 37%.

Abstract In this work, earth-abundant CZTSSe thin film solar cells were fabricated by sulfo-selenization of the Mo/Zn/Cu/Sn/Cu metallic precursors. The influences of morphological and compositional properties of the absorbers on performance of solar cells were investigated by tuning Cu content in the films. The Raman analysis showed that absorbers consist of a kesterite CZTSSe phase with ZnSe as a minor secondary phase. X-ray photoelectron spectroscopy (XPS) analyses revealed that the surfaces are Cu depleted and Zn enriched compared with the bulk composition of the absorbers. The results indicate that during sulfo-selenization the Cu diffused into the film and the Zn towards the film surface. The performance of the solar cells initially improved with the increasing of the Cu content and then decreased. By tuning the Cu content in the absorbers, the minority-carrier life time improved from 0.8 to 1.6 ns. The power conversion efficiency increased from 5.1 to 8.03% with fine controlling of Cu composition of the CZTSSe absorbers. The diode-ideality factors are higher than 2, suggesting an increased interfacial recombination in the devices. The high ideality-factors A and low minority carrier life times may originate from surface and bulk related defects, which in turn limits the Voc and the achievable high conversion efficiency for the CZTSSe thin film solar cells.

Abstract Ge alloyed Cu 2 SnS 3 (CTGS) thin films were prepared by annealing the sputtered deposited Cu-Ge-Sn precursor films under sulfur atmosphere at different annealing temperatures. The influence of different annealing temperatures on morphological, compositional, crystal structure of CTGS thin films were investigated. It was found that the annealing temperature of 550 °C provides a favorable sulfurization environment to promote grain growth leading to a compact thin film formation. Improved performance is ascribed to high Ge contents as evidenced from X-ray fluorescence (XRF) studies. Well incorporated Ge atoms into CTS thin film can be confirmed by X-ray diffraction (XRD). X-ray photoelectron spectroscopy (XPS) study provides an evidence of existence of Ge atoms where its binding energy located at 25.78 and 26.78 eV, respectively. However, the decreased performance was found at unsuitable annealing temperatures such as 500 °C, 520 °C, 580 °C and 600 °C. Finally, with annealing temperatures of 550 °C, the best power conversion efficiency (PCE) of 2.14% was attained with an open circuit voltage ( V oc ) of 220 mV, a short circuit current density ( J sc ) of 23.74 mA/cm 2 and a fill factor ( FF ) of 41%.