arXiv subjects

A. V. Sachenko

Publications and source records attributed to A. V. Sachenko.

23 records · Page 2Linked to original sources

arXiv2013

A new approach to simulation of limiting photoconversion efficiency of tandem solar cells

We develop a new approach to calculate the obtainable limit of photoconversion efficiency of tandem solar cells (SCs) and applied it to SCs with both vertical and lateral designs at AM0 and AM1.5 conditions. To get the maximum efficiency, only radiative recombination has been considered using typical radiative recombination parameters of the direct band gap III-V semiconductors, and explicit energy dependence of light absorption. When simulating the efficiency, we selfconsistently took into account the fact that the amount of the heat dissipated by SC decreases as the number of current-matched sub-cells increases. As the operating SCs temperature decreases both the open-circuit voltage and the photoconversion efficiency increase. It is shown that the above effect is especially strong for SCs operating under AM0 conditions. As the number of subcells is increased, narrowing the spectral range for each subcell, the photocurrent is additionally reduced due to the energy dependent light absorption, the factor generally ignored in the standard approaches. Application of our formalism results in a maximum in the theoretical dependence of the efficiency on the number of subcells, which was indeed observed experimentally. Besides agreement with experiment, our theoretical results are also close to other efficiencies calculated using detailed balance based approaches.

cond-mat.mtrl-sci↗

arXiv2013

Multijunction solar cells efficiency simulation

The radiative recombination, Shokley-Read recombination, frontal-surface and rear-surface recombination and the recombination at the heterojunction boundaries and the recombination in the space charge region are considered in the calculation of the multijunction solar cell (MSC) efficiency. The calculation is performed by a self-consistent solution of the equations for the photocurrent and photovoltage, as well as the heat balance equation. A cooling of MSC with the increase of the number of cells n and the improvement in the heat dissipation is regarded. It was found that, as the number of cells n is increased, narrowing of spectral range for each cell causes additional reduction of current. A substantial increase in the MSC efficiency can be achieved by improving the heat extraction using radiators and increasing emissivity. A comparison is made between the calculated and experimental efficiency values. A rather good agreement was found. A comparison between this calculation and other formalisms is given.

cond-mat.mtrl-sci↗

arXiv2013

Influence of surface centers on the effective surface recombination rate and the parameters of silicon solar cells

The results of our researches of the influence of exponentially distributed surface centers on the effective surface recombination rate and the parameters of silicon solar cells (SCs) are reported. In our calculations, we assumed the acceptor and donor surface states to lie in the upper and lower, respectively, parts of the bandgap. The model also supposed a discrete surface level to exist in the middle of the energy gap. In the case where the integrated concentration of continuously distributed centers is comparable with that of deep surface levels, those centers can affect the SC parameters only due to the recombination. If the concentration of continuously distributed centers is comparable or higher than the concentration characterizing a charge built-in into the insulator, those centers directly affect the surface band bending and the photo-induced electromotive force. With the help of a computer simulation, the conditions for the rate of surface recombination through continuously distributed surface centers to exceed that through the deep discrete level are determined. A decrease of the open-circuit voltage in inverted silicon SCs associated with the recombination through continuously distributed centers is calculated. The obtained theoretical results are compared with the experimental data.

cond-mat.mtrl-sci↗

arXiv2011

Temperature dependence of contact resistance of Au-Ti-Pd2Si-n+-Si ohmic contacts

We investigated temperature dependence of contact resistance of an Au-Ti-Pd2Si ohmic contact to heavily doped n+-Si. The contact resistance increases with temperature owing to conduction through the metal shunts. In this case, the limiting process is diffusion input of electrons to the metal shunts. The proposed mechanism of contact resistance formation seems to realize also in the case of wide-gap semiconductors with high concentration of surface states and dislocation density in the contact.

cond-mat.mtrl-sci↗

arXiv2011

Thickness dependences of photoelectric characteristics of silicon backside contact solar cells

The thickness dependences of the photocurrent quantum yield and photoenergy parameters of silicon backside contact solar cells (BC SC) are investigated theoretically and experimentally. The surface recombination rate on the irradiated surface was minimized by means of creating the layers of microporous silicon. A method of finding the surface recombination rate and the diffusion length of minority carriers from the thickness dependences of the photocurrent quantum yield under conditions of the strong absorption is proposed. The performed studies allowed us to establish that the thinning of the BC SC samples in the case of minimizing the surface recombination rate gives a possibility to achieve rather high efficiencies of photoconversion. It is also shown that the agreement between the experimental and theoretical spectral dependences of the photocurrent quantum yield can be reached only with regard for the coefficient of light reflection from the backside surface.

cond-mat.mtrl-sci↗