Silicon cells are the most expensive element used in photovoltaic systems. This reason and shortage of monocrystalline silicon lead us to developing concentrator approach.

There are a number of companies already acclaims about producing concentrator PV/T systems. Among them are Swedish cleantech company Arontis AB (Solar8, Fig.3, left), Canadian company Menova Energy Inc. (Power Spar, Fig.3, right), Spain company TRIGEN Solar S. L (GSH-20X, Fig.4, left), UK company HelioDynamics (HD16c with possible applications, Fig.3, right) [4].

Concentrator PV/T system built in the framework of research VEI project consists of 2D rotational frame, concentrator made with flat mirror facets and PV/T receiver. The project is devoted to

designing, building and testing of PV/T concentrator system based on solar cells with vertical p-n — junctions (Fig. 5).

Fig. 3 Solar8, left and Power Spar, right.

Fig.4. GSH-20X, left and HD16c with possible applications, right.

PV/T receiver includes row (array) of solar cells with vertical p-n-junctions in a case with quartz windows and special cooling liquid inside. PV/T receiver is designed for two side illumination because of ideal symmetrical design of solar cells with vertical p-n-junctions.

1.2. Solar cells with vertical p-n-junctions

Receiving element and solar cells for it are most important parts of concentrator PV/T systems.

The solar cells with vertical p-n-junctions are known as a good alternative of planar concentrator solar cells. They have a number of advantages: high temperature tolerance, low series resistance, bifacial sensitive accepting surfaces suitable for bifacial illumination, low equilibrium temperature,

quite simple technology of manufacturing etc. Low series resistance gives them to work under high concentration ration.

A method of manufacturing solar cells with vertical p-n-junctions using thermal compression bonding with silumin was developed in VEI and defended by Russian patents [5, 6]. The main goal of this technology is to provide a structure for a photovoltaic cell which gives as a result improved characteristics: improving quality of interconnecting soldering, eliminating of compensative influence of aluminum to n-layers, high temperature tolerance and mechanical firmness. The main stages of technology of producing solar cells with vertical p-n-junctions (without antireflection coating) are showed at Fig.6.

According to our approach, the silumin (alloy of Al and Si) layers prevent a penetration of compensative impurities (Al) into n — region. The produced solar cell structures give as a result the high quality mechanical and electrical contacts, high fill factor for I-V-characteristic (more than 0.8), and increased tolerance to high temperature under high intensity and higher tolerance to penetrating particle radiation (for space applications).

For optimization of technology processes the modern high resolution scanning microscopy methods of investigating vertical p-n-structures are used.