Thin Films of Tin Sulphide for Application in Photovoltaic Solar Cells

Tin sulphide (SnS) is a promising new material for use in photovoltaic solar cells. With a direct energy band gap of about 1.3 eV, and a high optical absorption coefficient, only a few microns of SnS are needed to absorb most of the incident light. Not only is SnS made of abundant, environmentally acceptable elements, it is also amphoteric giving flexibility to device design. Structures that can be envisioned include p-type SnS (absorber layer) / n-type (window layer) heterojunction devices, buried p-n junction devices made using SnS and p-i-n structure devices where the i-layer is SnS. It is most likely that the grain boundaries in SnS can be passivated either by counter-doping the grain boundaries, or by oxidizing the grain boundaries to form wide energy bandgap n-type SnO2 within p-type SnS, as dopants or oxygen will diffuse preferentially down the grain boundaries and react first at the grain boundary surfaces. Thin film solar cell devices based on the use of SnS have now been produced with efficiencies > 2 %; these and other promising results indicate that it is most likely that devices with efficiencies > 10% will be produced in the near future. Given that tin layers are routinely coated in industry over large area substrates and that industrial sulphidization processes are also well established, the industrialization of this technology should be more straightforward than that encountered with the already commercialised cadmium telluride and copper indium gallium diselenide thin film technologies. This review discusses the chemical and physical properties of SnS, the methods of producing both bulk crystals and thin films of SnS, the literature available on studies of SnS2 based photovoltaic solar cell devices, and progress made so far in developing this exciting new material

Nano-Photonic Structures for Light Trapping in Ultra-Thin Crystalline Silicon Solar Cells

Thick wafer-silicon is the dominant solar cell technology. It is of great interest to develop ultra-thin solar cells that can reduce materials usage, but still achieve acceptable performance and high solar absorption. Accordingly, we developed a highly absorbing ultra-thin crystalline Si based solar cell architecture using periodically patterned front and rear dielectric nanocone arrays which provide enhanced light trapping. The rear nanocones are embedded in a silver back reflector. In contrast to previous approaches, we utilize dielectric photonic crystals with a completely flat silicon absorber layer, providing expected high electronic quality and low carrier recombination. This architecture creates a dense mesh of wave-guided modes at near-infrared wavelengths in the absorber layer, generating enhanced absorption. For thin silicon (100 m) cells. There is potential for 20 m thick cells to provide 30 mA/cm(2) photo-current and >20% efficiency. This architecture has great promise for ultra-thin silicon solar panels with reduced material utilization and enhanced light-trapping

Tailoring of Interface Quality of MoOx/Si Solar Cells

Transition metal oxide films (TMO) as passivating contacts with improved opto-electronic characteristics play an important role in improving the silicon solar cell device efficiency. In this report, the effect of sputtering power on the optical properties of MoOx and the quality of MoOx/n-Si interface for its application in a silicon solar cell as carrier selective contacts has been reported. The optical transmittance of the film greater than 80 % in the visible and near infrared region of the spectrum is observed, which further improved with sputtering power. The creation of oxygen ion vacancies, which acts as positively charged structural defects able to capture one or two electrons led to the decrease of optical band gap from 3.70 eV to 3.23 eV at higher power. The oxygen vacancies occupied by electrons acts as donor centers, which lies close to the valence band, were responsible for modulation in electrical properties. The electrical properties of MoOx/n-Si interface was analyzed using current-voltage (I-V) measurements for its application as selective contact. A significant change in the selectivity parameters, like barrier height, I0 and series resistance of MoOx, has been observed with dc power. These extracted parameters showed that the sputtering power has a great influence on the selectivity of the charge carriers

Nano-Photonic Structures for Light Trapping in Ultra-Thin Crystalline Silicon Solar Cells

Thick wafer-silicon is the dominant solar cell technology. It is of great interest to develop ultra-thin solar cells that can reduce materials usage, but still achieve acceptable performance and high solar absorption. Accordingly, we developed a highly absorbing ultra-thin crystalline Si based solar cell architecture using periodically patterned front and rear dielectric nanocone arrays which provide enhanced light trapping. The rear nanocones are embedded in a silver back reflector. In contrast to previous approaches, we utilize dielectric photonic crystals with a completely flat silicon absorber layer, providing expected high electronic quality and low carrier recombination. This architecture creates a dense mesh of wave-guided modes at near-infrared wavelengths in the absorber layer, generating enhanced absorption. For thin silicon (<2 μm) and 750 nm pitch arrays, scattering matrix simulations predict enhancements exceeding 90%. Absorption approaches the Lambertian limit at small thicknesses (<10 μm) and is slightly lower (by ~5%) at wafer-scale thicknesses. Parasitic losses are ~25% for ultra-thin (2 μm) silicon and just 1%–2% for thicker (>100 μm) cells. There is potential for 20 μm thick cells to provide 30 mA/cm2 photo-current and >20% efficiency. This architecture has great promise for ultra-thin silicon solar panels with reduced material utilization and enhanced light-trapping

Polysilicon Films Formed on Metal Sheets by Aluminium Induced Crystallization of Amorphous Silicon: Barrier Effect

AbstractPolycrystalline silicon (pc-Si) thin films have been synthesized by aluminium induced crystallization (AIC) of amorphous silicon (a-Si) at low temperatures (≤500°C) on flexible metallic substrates for the first time. Different diffusion barrier layers were used to prepare stress free pc-Si films as well as to evaluate the effective barrier against substrate impurity diffusion. The layers of aluminum (Al) and then amorphous silicon with the thickness of 0.27 μm and 0.37 μm were deposited on barrier coated metal sheets by means of an electron beam evaporation and PECVD, respectively. The bi-layers were annealed in a tube furnace at different temperatures (400-500°C) under nitrogen flow for different time periods (1-10hours). The degree of crystallinity of the as-grown layers was monitored by micro-Raman and reflectance spectroscopies. Structure, surface morphology and impurity analysis were carried out by X-ray diffraction, scanning electron microscopy (SEM) and EDAX, respectively. The X-ray diffraction measurements were used to determine the orientation of grains. The results show that the AIC films on metal sheets are polycrystalline and the grains oriented in (100) direction preferentially. However, the properties of AIC films are highly sensitive to the surface roughness.</jats:p

Aluminum-Induced crystallization: Applications in photovoltaic technologies

[No abstract available

Thickness dependence of structure and optoelectronic properties of In2O3:Mo films prepared by spray pyrolysis

The influence of thickness on the structural, morphological and optoelectronic behavior of Mo-doped In2O3 films, prepared by spray pyrolysis was investigated. The films had the cubic crystal structure for all the thicknesses investigated although it was found that a change in the preferred orientation and growth mode, from 2D to 3D, has occurred with an increase of film thickness. A small degradation in the optical transmittance has been observed with the increase of film thickness. The variation of electrical resistivity, mobility and charge carrier concentration with film thickness were also studied and the results discussed