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Tin monosulfide (SnS) thin film is one of the most promising absorbers layer for high efficiency solar cells using low cost earth-abundant materials. To fabricate high quality SnS thin films, a simple nanoparticle based approach was employed in this work for phase pure material preparation using non-toxic solvents. Uniform SnS thin films were fabricated via a spin-coating process using phase pure SnS-ORT nanoparticle precursor solutions based on a methanol solvent, followed by post-annealing for grain growth. SnS thin film solar cells were then fabricated and their photovoltaic performance was characterized. The best SnS solar cell fabricated with the as-prepared SnS films with a band gap energy of ~1.25 eV showed a conversion efficiency of 0.12%.

To maximize the conversion efficiency of solar cells by improving the trapping of incident light, surface texturing of multicrystalline silicon wafers is a more permanent and effective solution to decrease reflections compared with antireflection coatings. In general, many techniques of wet chemical surface texturing depend on crystal orientation. Also, these processes place a limitation on the growth of solar production capacity due to consumption of the large amount of material, de-ionized water and chemicals. Reactive ion etching (RIE) is therefore useful for mc-Si solar cells with the random grain orientation. In this study, we have fabricated mc-Si solar cells with a large-area (156 mm × 156 mm) by a random RIE texturing method using SF 6 /O 2 plasma chemistry. A large amount of silicon loss, which is due to saw damage removal and texturing process of mc-Si wafers, have dramatically decreased by applying RIE texturing process. As a result of the optimum RIE process, the best mc-Si solar cell showed conversion efficiency, fill factor, short circuit current density, and open circuit voltages as high as 17.4%, 80%, 35 mA/cm 2 and 620 mV, respectively. This study demonstrates that it is possible to apply the thin mc-Si Solar cells fabrication for low cost and high efficiency in conventional industrial production line.

For low-cost fabrication applications, Cu 2 − x Se thin films were fabricated by a non-vacuum process and were then characterized in terms of quality. Cu–Se nanoparticles were synthesized by a low-temperature colloidal method and were confirmed to be Cu 2 − x Se nanoparticles by X-ray diffraction and Raman spectroscopy. The synthesized Cu 2 − x Se nanoparticles were deposited as films by a direct non-vacuum coating method, and the as-deposited Cu 2 − x Se thin films were selenized at different reaction temperatures, reaction times, and Se fluxes. The selenized films presented several distinct characteristics that depended on their fabrication conditions. Well-grown Cu 2 − x Se thin films were obtained at high reaction temperatures, long reaction times, and high Se fluxes. In addition, the selenized Cu 2 − x Se layer was observed to have a larger Cu content than the Cu 2 − x Se nanoparticles.

We investigated the transport and photovoltaic properties of Cu-deficient Cu(In1 − xGax)Se2 (CIGS) thin-film solar cells containing ordered vacancy compound (OVC) layers. Raman spectra clearly revealed that the CIGS thin films with lower Cu concentrations contained larger volumes of OVC layers. The temperature-dependent inverse ideality factor showed that the CIGS film containing more (less) OVC layers exhibited tunneling-mediated bulk (interface)-dominated recombination. The capacitance–voltage characteristics and admittance spectra showed that the CIGS cells containing more OVC layers had more uniform carrier concentration near the junction and less interfacial trap states compared with cells with less OVC layers. These results suggested that the Cu-deficiency and the resulting OVC layer formation reduced the interfacial defect density and suppressed the interface recombination processes of the CIGS solar cells.

The influence of the conventional depositing processes on the optical properties of Cu(In,Ga)Se 2 (CIGS) thin films in solar cell structures was investigated by measuring the photoluminescence (PL) and Raman spectra of the CIGS layer at each stage of the solar cell deposition process. The intensities of the PL and the Raman A 1 mode increase after the CdS buffer layer is deposited, suggesting that the CdS layer either improves the optical quality of the CIGS film or protects it from degradation due to environmental factors. The temperature and excitation power dependences of the PL for the bare CIGS sample are very different from those for the samples with the CdS layer, reflecting different characters of the luminescence centers near the surface of the CIGS layer. On the other hand, the lateral homogeneity, as seen in the micro-PL and micro-Raman images, does not seem to improve. After the ZnO window layer is deposited, the overall PL and Raman intensities do not change much, although the intensity distribution becomes more inhomogeneous.

Cu 2 ZnSnSe 4 (CZTSe) thin films were deposited on Mo-coated soda–lime glass substrates by single-stage co-evaporation process and the effect of substrate temperature ( T sub ) was investigated on the CZTSe thin film growth during the process. The film thickness decreased and the grain size increased with increasing T sub . The optimum substrate temperature to obtain CZTSe films was found to be 593 K. The film grown at T sub of 773 K seems to have the phase decomposition into Cu x Se and ZnSe, probably because of Sn loss during the process. The best cell fabricated with a CZTSe absorber layer grown at T sub of 593 K produced 2.88% of conversion efficiency.

The photovoltaic properties of CIGS cells on an alumina substrate were improved through the use of Na-doped Mo as the bottom layer of a Mo back contact. Na was supplied to the CIGS bulk region from an alumina/Na-doped Mo/Mo structure, similar to the Na diffusion from soda-lime glass. The diffusion of Na from the Na-doped Mo was controlled effectively compared to that from Soda-lime glass (SLG). The present results indicate that Na-doped Mo acts as a Na source material and that the Na amount can be controlled by adjustment of thickness of Na-doped Mo layer, without the use of an alkali barrier layer. The highest conversion efficiency of 13.34% ( J sc = 34.62 mA/cm 2 , V oc = 0.58 V and FF = 66%) for an active area of 0.45 cm 2 on an alumina substrate was obtained for 100 nm Na-doped Mo/1000 nm Mo.

Cu(In,Ga)Se2 (CIGS) nanoparticles as a precursor material of a thin absorber layer for the CIGS based solar cells were synthesized by the relatively simple colloidal process. CIGS nanoparticles of 15–80 nm in diameter were obtained by reacting a mixture of CuI, InI3 and GaI3 in pyridine with Na2Se in methanol at 0 °C in nitrogen atmosphere with mechanical stirring. As the reaction time increased from 0 to 1 min. the size of nanoparticle decreased, showing a minimum at 1 min. (about 15 nm in diameter with very small size distribution). Further increase in the reaction time resulted in an increase in the nanoparticle size. The change in the size of CIGS nanoparticles with the reaction time was analyzed in terms of the effects of mechanical stirring on the concentration distribution of solute, i.e., CIGS nuclei, in the colloidal solution, and hence on the nucleation and the subsequent growth processes of the CIGS nanoparticles.

The structure of passive film formed on Ti in pH 8.5 buffer solution was examined by comparing the photocurrent for both the passive film and the thermally grown oxide on Ti in air at 400 °C. The passive films formed on Ti in pH 8.5 buffer solution showed optical band gap energy of 3.36 eV, while the thermally grown oxide film on Ti was found to have band gap energy of 3.1 eV. The higher value of band gap energy of passive film was attributed to the less crystalline or more disordered structure of passive film compared to that of the thermal oxide. This fact was supported by the higher disorder energy of passive film, determined from the absorption tail of photocurrent spectrum, than that of thermal oxide.