To accurately calculate efficiencies η of experimentally produced multijunction solar cells (MJSCs) and optimize their parameters, we offer semi-analytical photoconversion formalism that incorporates radiative recombination, ShockleyRead-Hall (SRH) recombination, surface recombination at the front and back surfaces of the cells, recombination in the space charge region (SCR) and the recombination at the heterojunction boundaries. Selfconsistent balance between the MJSC temperature and efficiency was imposed by jointly solving the equations for the photocurrent, photovoltage, and heat balance. Finally, we incorporate into the formalism the effect of additional photocurrent decrease with an increase of subcell number. It is shown that for an experimentally observed Shockley-Read-Hall lifetimes, the effect of re-absorption and re-emission of photons on MJSC efficiency can be neglected for non-concentrated radiation conditions. A significant efficiency η increase can be achieved by improving the heat dissipation using radiators and bringing the MJSC emissivity to unity, that is closer to black body radiation rather than grey body radiation. Our calculated efficiencies compare well with other numerical results available and are consistent with the experimentally achieved efficiencies. The formalism can be used to optimize parameters of MJSCs for maximum photoconversion efficiency.Index Terms -multijunction solar cells, efficiency, III-V compound semiconductors, radiative and nonradiative recombination.

The conversion of energy of electrons produced by a radioactive β-source into electricity in a Si and SiC n p  junctions is modeled. The features of the generation function that describes the electron-hole pair production by an electron flux and the emergence of a "dead layer" are discussed. The collection efficiency Q that describes the rate of electron-hole pair production by incident beta particles, is calculated taking into account the presence of the dead layer. It is shown that in the case of high-grade Si n p  junctions, the collection efficiency of electron-hole pairs created by a high-energy electrons flux (such as, e.g., Pm-147 beta flux) is close or equal to unity in a wide range of electron energies. For SiC p -n junctions, Q is near unity only for electrons with relatively low energies of about 5 keV (produced, e.g., by a tritium source) and decreases rapidly with further increase of electron energy. The conditions, under which the influence of the dead layer on the collection efficiency is negligible, are determined. The open-circuit voltage is calculated for realistic values of the minority carriers' diffusion coefficients and lifetimes in Si and SiC n p  junctions, irradiated by a high-energy electrons flux. Our calculations allow to estimate the attainable efficiency of betavoltaic elements.

Abstract. We review a status of the research on conversion of solar energy into electricity by using the systems that split the solar spectrum with a set of luminescent concentrators. Influence of the luminophore choice (rare-earth elements, dyes, or semiconductor quantum dots) and their characteristics as well as the luminescence quantum losses, when the light quanta travel inside the optical waveguide formed by the luminescent concentrator, were analyzed. The methods to minimize these losses, including optimal converter design, were discussed. The choice of design with stacked luminescent concentrators was demonstrated. The design of the stacked luminescent concentrators with optimized parameters of the transparent matrix and semiconductor quantum dots was investigated.

Conversion of energy of beta-particles into electric energy in a p-n junction based on directbandgap semiconductors, such as GaAs, considering realistic semiconductor system parameters is analyzed. An expression for the collection coefficient, Q, of the electron-hole pairs generated by beta-electrons is derived taking into account the existence of the dead layer. We show that the collection coefficient of beta-electrons emitted by a 3 H-source to a GaAs p-n junction is close to 1 in a broad range of electron lifetimes in the junction, ranging from 10 −9 to 10 −7 s. For the combination 147 Pm/GaAs, Q is relatively large (≥ 0.4) only for quite long lifetimes (about 10 −7 s) and large thicknesses (about 100 µm) of GaAs p-n junctions. For realistic lifetimes of minority carriers and their diffusion coefficients, the open-circuit voltage realized due to the irradiation of a GaAs p-n junction by beta-particles is obtained. The attainable beta-conversion efficiency η in the case of a 3 H/GaAs combination is found to exceed that of the 147 Pm/GaAs combination.

Abstract. In this work, features of solar cells of lateral type were analyzed. The authors offered a design of a monolithic compact solar module with cells electrically connected in series and with a dispersion element (holographic grating). Simulation of a multistage converter was carried out. It has been shown that with increasing the number of cells n the maximum limited efficiency  increases. Its maximum values up to  ≈ 53.6% are reached for n = 15 (in the case of perfectly matched semiconductors and conditions AM0). With further increase of n , the efficiency decreases. For a set of concrete semiconductors  ≈ 45% the maximum efficiency for AM0 conditions may be achieved, when the number of cells equals 4. It has been shown that the calculation results agree with experimental data. The possibility of technical implementation of solar cells with using inkjet printers was investigated, too. Briefly discussed have been the properties of these printers, as well as metal, semiconductor and dielectric inks.