N.R. Mathews

Development of CdTe thin films on flexible substrates—a review

In the recent years there has been an increased interest in photovoltaic structures on lightweight flexible substrates. Photovoltaic structures on lightweight substrates have several advantages over the heavy glass-based structures in both terrestrial and space applications. CdTe is one of the leading candidates for the solar cells due to its optimum band gap and the variety of film preparation methods. The development of CdTe thin films on flexible substrates is discussed. The film growth and characterization are reviewed.

Photoelectrochemical characterization of porous Si

Abstract The photoelectrochemical measurements of p-Si and porous silicon in 0.1 M H2SO4 were done. The band gap of Si is a bit low for efficient hydrogen production. The silicon was made porous to improve the efficiency of hydrogen production. The porous silicon photocathodes show a substantial improvement in the hydrogen production compared to that of p-Si photocathodes. Studies were done by applying different light flux on the porous silicon.

Influence of the deposition potential on the structure and composition of the CdTe films electrodeposited on stainless steel substrates

The dependence of the chemical composition and grain growth on the deposition potential of CdTe films on stainless steel substrates has been investigated. The preliminary analysis using XRD, EPMA and AUGER techniques show that the preferential orientation of the CdTe grains and the percentage composition of the film depend on the potential applied between the reference electrode and the stainless steel substrate. It is possible to control the composition of the electrodeposited CdTe films by properly adjusting the deposition potential. AUGER analysis revealed the presence of oxygen throughout the thickness of the film.

Photoelectrochemical characterization of SiC

The current-voltage (I-V) studies for p-SiC in KOH and n-SiC in Na 2 SO 3 in a two-electrode configuration indicated that SiC-based photoelectrochemical systems can be a possibility for water splitting. With illumination there is appreciable photocurrent generation at the semiconductor-electrolyte interface, which correspond to water splitting to form hydrogen and oxygen at the respective electrodes. The C-V analysis gave an idea about the flat-band potential and carrier concentration.

Development of wide band gap Cd1-XMgXTe/CdS top cells for tandem devices

In order to achieve advances in CdTe technology, we are continuing our efforts in developing wide band gap ternary alloy films based on CdTe. This approach will help in harnessing the already existing CdTe technology to develop high efficiency tandem devices. The band gap of Cd1-xMgxTe can be easily tuned from 1.48 to 1.8 eV (x=0 to 0.17). Close match of the lattice constant of MgTe with CdTe and the apparent complete miscibility of MgTe in CdTe and the rapid increase in band gap with Mg content gives the flexibility to prepare material with appropriate band gap for current- matching in a tandem solar cell. In this paper development of Cd1-xMgxTe films by vacuum co-evaporation and prototype Cd1-xMgxTe/CdS solar cells are reported. The co-evaporated films on large area substrates exhibited high spatial uniformity. We have used different experimental techniques such as XRD, Raman, PL, UV-VIS spectroscopy, and opto-electronic tools for studying the effect of Mg incorporation in to the lattice of CdTe. Evidences of lattice perturbations due to the incorporation of Mg were observed in XRD and Raman data, however no phase segregation was observed in the XRD spectra. We are continuing our investigation of the effect of post deposition chloride treatment and annealing on the band gap stability of the Cd1-xMgxTe films. Films chloride treated with MgCl2 exhibited better stability compared with those films annealed in CdCl2 vapor. However, our preliminary data on the CdS/Cd1-xMgxTe devices show that CdCl2 vapor treatment is beneficial for attaining better efficiency. Prototype devices of the configuration Tec7/CdS/Cd1-xMgxTe/Cu-Au was developed with Cd1-xMgxTe films with different x values. Efficiency varies in the range 2 to 4.6% depending on the band gap of the absorber.

Synthesis and Characterization of SnS Nanoparticles through a Non-Aqueous Chemical Route for Depositing Photovoltaic Absorber Layers

SnS nanocrystals of sub-10 nm in size were synthesized by a room temperature, non-aqueous chemical route in the presence of different amounts of triethanolamine (TEA) used as a complexing agent. The crystallinity, size, morphology, chemical composition and optical properties of the as-prepared SnS nanoparticles were investigated by powder X-ray diffraction (XRD), high-resolution transmission electron microscopy (HRTEM), Energy-dispersive X-ray spectroscopy (EDS), micro Raman and optical absorption spectroscopy. The XRD analysis and HRTEM investigation of SnS nanoparticles confirmed the presence of crystalline orthorhombic SnS phase. Upon increasing the amount of TEA, the crystallite size of the samples decreased gradually showing evidence of quantum confinement. EDS analysis showed that SnS nanoparticles (NPs) grown in absence of TEA were highly stoichiometric whereas in TEA capped samples, the atomic concentration of S is slightly higher than that of Sn. As-synthesized SnS nanocrystals displayed strong absorption in the visible and near-infrared spectral regions followed by a blue shift of their absorption edge on increasing the TEA concentration. These nanoparticles were used to prepare SnS paste which was deposited on conducting glass substrates to obtain thin films for photovoltaic applications. The crystallinity, morphology, chemical composition and optical properties of annealed SnS films were investigated.