StatusThe thesis was presented on the 25 February, 2011
Approved by NCAA on the 31 March, 2011
Abstract– 1.21 Mb / in romanian
In the thesis are presented the results of the elaboration of a simple and inexpensive technology of solar cells fabrication with enlarged active area up to 78,5cm2 on the base SIS nSi/SiO2/n+ITO structures, including a new type of bifacial solar cells, which contains only isotype junctions. Tandem microamorphouse solar cells with enlarged efficiency on the base of Si thin films were also fabricated and the investigation of the electrical and photoelectric properties of all types of the elaborated solar cells has been carried out.
The topicality and the importance of the examined problem, the novelty, the aim and the objectives of the thesis are formulated. A detailed analysis of the special literature concerning the silicon solar cell- history, achievements and perspectives is considered.
The technology of SnO2 and In2O3:SnO2 (ITO) thin films obtaining by means of spraying of alcoholic solution of InCl3 and SnCl4 in different proportions on the nSi crystals was elaborated. Wafers oriented in the (100) plane with the diameter of 100mm have been used for the fabrication of photovoltaic devices. The dependence of the photovoltaic parameters on the Si crystals conductibility was studied. Optical and ohmic losses in dependence on the thickness and the conductibility of the ITO frontal layer were determined. The conditions of the SiO2 insulated layer obtaining at the ITO-nSi interface and their influence on the solar cell photoelectrical parameters was investigated. The optimization of the of solar cells obtaining on the base of n+ITO/SiO2/nSi junctions allow to the elaboration of the technical documentation of the solar cell fabrication with 10,25% efficiency. The viability of the elaborated technology was confirmed by the fabrication in laboratory conditions of a small series of photovoltaic devices and the assemblage on their base solar modules with a power of 36W, measured at daylight (700-740W/m2).
For the first time the conception and the design of a bifacial solar cell with isotype junctions was elaborated. This solar cell contains two isotype junctions. One of them is formed on the frontal side of the Si wafer, the second – on the rear side. At first, the n+-nSi junction at the rear side is formed by phosphor diffusion from the liquid source POCl3 during 15 - 105min.at the temperature of 850°С. After the diffusion the wafers are annealed at the temperature of 940°С during 180 minutes. As a result a 0,1eV heights potential barrier, situated at the depth of 0,8- 1,0m from the rear surface, is formed. The frontal junction is obtained by the above-mentioned spraying process. The energetic band diagram of such n+ITO/SiO2/nSi/n+Si solar cell is proposed and evaluated. The integral tandem photovoltaic system was fabricated; their electrical and photoelectric properties have been studied. So, the viability of a new type of photovoltaic device with bilateral sensitivity was demonstrated. The succession of the technological steps which are necessary for the fabrication of a new type of n+ITO/SiO2/nSi/n+Si bifacial solar cells with 15,7% efficiency is described.
The principle of realization and the results of investigation of the properties of tandem microamorphouse solar cells on the base of p-i-n the amorphous and microcrystalline junctions, obtained by the method of plasma assisted chemical vapour deposition (PECVD) is presented. These structures combine into one the advantages of the amorphous silicon and of the technology of the stabilization and of the sensitivization of the structures, obtained on their base and demonstrated a stable value of the efficiency (η=11,1%). Solar modules with the area of 0,01m2 and the power up to1W, were fabricated.
The obtained results are reflected in 31 scientific papers, one patent and were presented at
18 International conferences and 7 International exhibitions and salons.