A Three Stage Selenization Process for the Preparation of High Efficiency CuInGaSe2/ CdS Thin Films Solar Cells

CuGaInSe2/CdS thin film solar cell with an efficiency in excess of 15% have been prepared by a novel three stage selenization method. The first stage consists in the deposition of Cu, In Ga elemental layer on Mo covered soda lime glass and selenization of the layers in a Se vapour. For the second and third stage only Cu and Ga are used as elemental layers in order to increase the amount of Ga in CuGaInsSe2 film

Lock-in EBIC studies of CdS/CdTe solar cells grown by high vacuum evaporation

The use of an electostatically blanked electron beam has allowed the application of phase sensitive detection to the electron beam-induced current technique. This has allowed the recovery of smaller induced signals, even from films of low mechanical integrity following substrate removal. This technique has been applied to CdTdCdS solar cells deposited by the high vacuum evaporation technique. EBlC images of untreated and chloride treated devices suggest that this treatment produces higher efficiency regions near CdTe grain boundaries than In the grain interiors. This is explained by the collecting junction being closer to the CdStCdTe interface in the near boundary regions. compared with a more deeply buried junction within the grains. This conclusion is supported by beam voltage dependent EBIC measurements, which show unexpectedly efficient collection deep in the absorber layer. Comparison with previous work implies that this variation in junction position is due to higher doping near the grain boundaries

Effect of back contact metallization on the material stability of CdTe/CdS solar cells

The electrical contact on CdTe is important for the high efficiency and long term stability of CdTe/CdS solar cells. As most of the metals form a Schottky barrier on p-type CdTe, a buffer layer is needed to reduce the effective barrier height and enhance the acceptor concentration at the back contact. In order to obtain stable but highly efficient cells we investigated different back contact materials and etching procedures. Accelerated life time tests revealed the stability of the cells. CdTe/CdS cells with Al or Au metallization showed degradation, whereas Mo metallization produced very stable cells with Sb2Te3 and Sb buffer layers. These cells have up to 10 % efficiency after 9 months accelerated life time tests which corresponds to 75 years under normal conditions. The barrier height and the doping profile have been measured with C-V characteristics

Development of High Efficiency Flexible CdTe Solar Cells

Polycrystalline thin film solar cells of II-VI compound semiconductors are important because of their low cost, high efficiency and stable performance. Flexible and lightweight solar cells are interesting for a variety of terrestrial and space applications that require a very high specific power (ratio of output electrical power to the solar module weight). Moreover, light modules are advantageous in terms of transport and mounting. We have previously described the development of flexible CdTe/CdS solar cells on polyimide substrates with a novel method; efficiencies of 8.6 % were reported. Further improvements in the processing have now increased the solar cell efficiency to 11%. The CdTe solar cell is fabricated in a \u201csuperstrate\u201d configuration where the light passes through the polyimide substrate. Absorption of the incident light and possible degradation of polyimide under UV and particle irradiation are the major limitations of this configuration. To overcome these a new approach is introduced here. The CdTe/CdS/TCO stacks are grown on a NaCl/glass substrate. After the solar cell has been processed, a polymer layer is spin coated on top and the flexible solar cells are detached from the glass by dissolving the NaCl buffer layer. Solar cells of 7.3% efficiency have been obtained

Influence of Transparent Conducting Oxides on the Properties of CdTe/CdS Solar Cells

Transparent conducting oxides (TCO), such as indium tin oxide (ITO), fluorine doped tin oxide (FTO), and Al doped zinc oxide (ZnO), have been used as transparent electrodes in CdTe/CdS thin film solar cells. The merits of different TCOs and the properties of the CdTe/CdS solar cells in superstrate configuration have been investigated. The average transmission of CdS/FTO is 80% while CdS/ZnO window layers have a lower transmission of 40 to 60%. Effects of CdCl2 treatment on the recrystallization of CdTe have been studied with XRD and SEM. A large increase in the grain size along with the loss of the (111) preferred orientation are measured. Recrystallization is similar on ZnO and FTO but different on ITO. The performance of solar cells on different TCOs depends on the amount (thickness) of CdCl2. For higher efficiencies, more CdCl2 is required for CdTe/CdS/FTO in comparison to CdTe/CdS/ITO

Bifacial Thin Films Solar Cells

A thin film photo-voltaic device formed on a transparent substrate 41 comprises a p-type semiconductor layer 44, and an n-type semiconductor layer 43 forming a p-n junction at the interface with the p-type layer 44. Transparent conducting oxide (TCO) contacts 42 46 are provided on the p-type 44 and n-type 43 layers to form a device which converts radiation 40 47 incident on both front and back surfaces into electricity. The surface 45 of the p-type layer 44 contacting the TCO contact 46 is modified such that a buffer layer between the p-type layer 44 and the TCO contact 46 is not required. The photo-voltaic device can be stacked in tandem formation with other photo-voltaic devices to gather radiation at different wavelengths

Cadmium and Zinc Chloride Treatments of CdS films for the preparation of High Efficiency CdTe/CdS Thin Films Solar Cells

CdTe/CdS thin film solar cells exhibiting conversion efficiency close to 14% have been prepared on glass substrates by treating the CdS film with ZnCl2 and CdCl2. This treatment has shown to be effective in rendering the CdS film less reactive with CdTe when this is deposited on top of CdS by Close Spaced Sublimation at a substrate temperature of 500-520\ub0C. This limits the interdiffusion between CdS and CdTe during the cell preparation and improves both the open-cicruit voltage and fill factor of the solar cell

Congenital muscular dystrophy with muscle inflammation, alpha dystroglycan glycosylation defect and no mutation in FKRP gene

Congenital muscular dystrophies (CMD) are autosomal recessive infantile disorders characterized by dystrophic changes at muscle biopsy and contractures. Central nervous system (CNS) abnormalities associated with mental retardation are often present. We describe a patient affected with muscle weakness, psychomotor developmental delay and normal brain MRI. Muscle biopsy showed complete absence of the \u3b1-dystroglycan (DG) glycosylated epitope and preservation of \u3b1-dystroglycan (\u3b1-DG) protein core. The analysis of FKRP, LARGE, POMT1 and POMGnT1 genes did not show any pathogenic mutations, suggesting that at least another gene may account for CMD with secondary glycosylated \u3b1-DG deficiency

High Efficiency flexible CdTe solar cells on polymer substrates

Flexible superstrate solar cells were directly grown on commercially available 10 mm thin polyimide (UpilexTM) foils. A process for the deposition of ITO (front contact) has been developed to have a stable front contact on the UpilexTM foil. Post-deposition annealing treatments of the ITO/polyimide stacks bring a significant stability to the front contact, having almost the same sheet resistance at the beginning and at the end of the cell fabrication process. Solar cells with AM1.5 efficiency of 11.4% on UpilexTM foils (highest efficiency recorded for flexible CdTe cell) have been developed. A comparison of the cells prepared on different polyimides is presented