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Development of Flexible single and tandem II-VI-Based High Efficiency Thin Film Solar Cells

Final Report Summary - FLEXSOLCELL (Development of Flexible single and tandem II-VI-Based High Efficiency Thin Film Solar Cells)

The primary aim of this research project was to carry on the development of low cost thin film photovoltaic devices. The routes to decrease the “cost per Watt” are either to reduce the cost of the technology or to increase its efficiency. The first route was addressed by the use of thin film technology for low cost deposition with low material usage and activation treatments at low temperatures. The second route was addressed by using multiple threshold devices to push efficiencies beyond the Schockley-Queisser limit for single junction PV cells. Our research activities were focused on the study and development of CdS, ZnSe and CdTe thin films for both PV and optoelectronic applications.
The main goal of this project was to develop the polycrystalline growth techniques for high efficiency CdS/CdTe and ZnSe/CdTe solar cells on glass and polyimide substrates in different substrate configurations. Continuation of the joint research towards development of commercially viable CdTe-based solar cells was built on the research collaboration which successfully combined: (a) the fabrication of glass and flexible solar-cell by close space sublimation (CSS) and hot wall technique (HWT) at Moldova State University; (b) Raman and Photoluminescence spectroscopy and XRD characterization techniques at University of Trieste, Italy; and (c) the chemical bath deposition (CBD) of CdS, electrodeposition of CdTe, characterization and analysis expertise in the mechanism of CdCl2 treatment process, annealing ambient and formation of optoelectronic properties of the layers and junctions at Tallinn University of Technology, Estonia. The most important achievements of the project were (1) increased cell efficiency to near 12 % by improvements in electrical properties of the materials and reductions in window-layer absorption, (2) demonstration that cell stability can be reasonably extrapolated to several years, and (3) enhanced measurement and analysis capability in Moldova.
The project has established and reinforced a long-term research co-operation between the universities of MSU, TUT and UniTs through a coordinated joint programme of exchange of researchers for short periods and also through the coordinated collaboration, conducted by the information flow through the electronic channels. Researchers from low-income country like Moldova, had high motivation to be involved in the EU countries Italy and Estonia to enjoy the normal working standards with Hi-Tech research apparatus. Also the partner universities and goverment investment organizations (Department of Education and Science), the assistance programs (Archimedes, FP7 NCP) had high motivation for additional financing of the project together with doctoral and postdoctoral positions for Moldavian and Estonian researchers.
This project contributed significantly to the high-tech development in the participating countries. The mobility/exchange program gave the possibility to improve and update the scientific knowledge and the technical skills of the scientists involved in the FLEXSOLCELL project. The strong collaboration especially with TUT and UniT’s partners contributed to the productivity of MSU. Due to trained researchers during the organized meetings and trainings in MSU, UniTs and TUT have been established new laboratories for the research of photovoltaic materials and solar cells. Within the framework of our FLEXSOLCELL research program a CdS/CdTe photovoltaic minimodules with fixed voltage 3 V was fabricated for small power consumers, such as calculators, mobile phones or other small electrical power.