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The recombination rate in the space charge region (SCR) of a silicon-based barrier structure with a long Shockley-Reed-Hall lifetime is calculated theoretically by taking into account the concentration gradient of excess electron-hole pairs in the base region. Effects of the SCR lifetime and applied voltage on the structure ideality factor have been analyzed. The ideality factor is significantly reduced by the concentration gradient of electron-hole pairs. This mechanism provides an increase of the effective lifetime compared to the case when it is insignificant, which is realized at sufficiently low pair concentrations. The theoretical results have been shown to be in agreement with experimental data. A method of finding the experimental recombination rate in SCR in highly efficient silicon solar cells (SCs) has been proposed and implemented. It has been shown that at the high excess carrier concentration exceeding 1015 cm-3 the contribution to the SCR recombination velocity from the initial region of SCR that became neutral is significant. From a comparison of theory with experiment, the SCR lifetime and the ratio of the hole to the electron capture cross sections are determined for a number of silicon SCs. The effect of SCR recombination on the key characteristics of highly efficient silicon SCs, such as photoconversion efficiency and open-circuit voltage, has been evaluated. It has been shown that they depend not only on the charge carrier lifetime in SCR, but also on the ratio of hole to electron capture cross sections σp/σn. When σp/σn < 1, this effect is significantly strengthened, while in the opposite case σp/σn > 1 it is weakened. It has been ascertained that in a number of highly efficient silicon SCs, the distribution of the inverse lifetime in SCR is described by the Gaussian one. The effect described in the paper is also significant for silicon diodes with a thin base, p-i-n structures, and for silicon transistors with p-n junctions. In Appendix 2, the need to take into account the lifetime of non-radiative excitonic Auger recombination with participation of deep impurities in silicon is analyzed in detail. It has been shown, in particular, that considering it enables to reconcile the theoretical and experimental dependences for the effective lifetime in the silicon bulk. [ABSTRACT FROM AUTHOR]

An expression for finding the dependence of narrowing the bands in silicon Eg on the level of illumination from the intrinsic absorption band (or short-circuit current) has been proposed. This expression is used to find experimental values of Eg in high-efficient silicon solar cells. The dependence Eg (J) or dependence Eg (JI), where JI is the shortcircuit current density, has been rebuilt into the Eg (nOC) dependence, where nOC is the excitation level in open-circuit conditions. With this aim, the generation-recombination balance equation was solved taking into account six recombination mechanisms in silicon, including Shockley-Reed-Hall recombination, radiative recombination, interband Auger recombination, surface recombination, non-radiative exciton recombination, and recombination in the space charge region. The latter two recombination terms are not taken into account in studies of the key parameters of silicon solar cells and in programs for simulating the characteristics of these solar cells. Therefore, in this work their correct definition was performed, their contribution was compared with the contribution of other recombination mechanisms, and it has been shown that the description of the characteristics and key parameters of silicon SC without taking them into account is insufficiently correct. The experimental dependences Eg (nOC) obtained in the work were compared with Schenk's theory. It has been shown that there is a good agreement between them. [ABSTRACT FROM AUTHOR]

Theoretical modeling of the optical and photovoltaic characteristics of highly efficient textured silicon solar cells (SC), including short-circuit current, open-circuit voltage and photoconversion efficiency, has been performed in this work. In the modeling, such recombination mechanisms as non-radiative exciton recombination relative to the Auger mechanism with the participation of a deep recombination level and recombination in the space charge region (SCR) was additionally taken into account. In a simple approximation, the external quantum efficiency of the photocurrent for the indicated SC in the long-wavelength absorption region has been simulated. A theory has been proposed for calculating the thickness dependences of short-circuit current, open-circuit voltage and photoconversion efficiency in them. The calculated dependences are carefully compared with the experimental results obtained for SC with the p + -i-α-Si:H/n-c-Si/i-n + -α-Si:H architecture and the photoconversion efficiency of about 23%. As a result of this comparison, good agreement between the theoretical and calculated dependences has been obtained. It has been ascertained that without taking into account recombination in SCR, a quantitative agreement between the experimental and theoretical light I-V characteristics and the dependence of the output power in the SC load on the voltage on it cannot be obtained. The proposed approach and the obtained results can be used to optimize the characteristics of textured SC based on monocrystalline silicon. [ABSTRACT FROM AUTHOR]

Crystalline Silicon (c-Si) remains a dominant photovoltaic material in solar cell industry. Currently, scientific and technological advances enable producing the c-Si solar cells (SCs) efficiency close to the fundamental limit. Therefore, combining the experimental results and those of modeling becomes crucial to further progress in improving the efficiency and reducing the cost of photovoltaic systems. We carried out the experimental characterization of the highly-efficient c-Si SCs and compared with the results of modeling. For this purpose, we developed and applied to the samples under investigation the improved theoretical model to optimize characteristics of highly efficient textured solar cells. The model accounts for all recombination mechanisms, including nonradiative exciton recombination by the Auger mechanism via a deep recombination centers and recombination in the space-charge region. To compare the theoretical results with those of experiments, we proposed empirical formula for the external quantum efficiency (EQE), which describes its experimental spectral dependence near the long-wave absorption edge. The proposed approach allows modeling of the short-circuit current and photoconversion efficiency in the textured crystalline silicon solar cells. It has been ascertained that the dependences of the short-circuit current on the open-circuit voltage and the dark current on the applied voltage at V < 0.6 V coincide with each other. The theoretical results, as compared to the experimental ones, allowed us to validate the developed formalism, and were used to optimize the key parameters of SCs, such as the base thickness, doping level and others. In this work, we have further generalized and refined the analytical approach proposed and used by us earlier to analyze high-efficiency solar cells and model their characteristics. [ABSTRACT FROM AUTHOR]

Short-circuit current, open-circuit voltage, and photoconversion efficiency of silicon high-efficiency solar cells with all back contact (BCSC) with planar surfaces have been calculated theoretically. In addition to the recombination channels usually considered in this kind of modeling, namely, radiative, Auger, Shockley-Read-Hall, and surface recombination, the model also takes into account the nonradiative trap-assisted exciton Auger recombination and recombination in the space charge region. It is ascertained that these two recombination mechanisms are essential in BCSCs in the maximum power operation regime. The model results are in good agreement with the experimental results from the literature. [ABSTRACT FROM AUTHOR]

The properties of the synthesized films of organic-inorganic perovskites CH3NH3PbI3 obtained at various ratios of starting reagents (PbI2 and CH3NH3I) have been studied. As a solvent, we used chemically pure dried dimethylformamide (DMF). Organicinorganic perovskites are promising for photovoltaic applications. It has been shown that regardless of the ratio of the starting reagents, single-phase perovskites are formed, at the same time the microstructure of the films changes significantly. It has been reported photoelectric and optical properties of synthesized films, namely: experimental and theoretical spectral dependences of the low-signal surface photovoltage and transmission. The band gap and the Urbach parameter dependence on the ratio of precursors were determined. It has been found that the materials' band gap depends on the ratio of precursors and equals to 1.59, 1.62 and 1.57 eV, while the characteristic Urbach energy equals to 18, 19 and 22 meV for the PbI2:CH3NH3I films with PbI2 ratio of 1:1, 1:2 and 1:3, respectively. It has been ascertained that the spectral dependences of the low-signal surface photovoltage are much more sensitive to the material microstructure and its electronic structure close to the absorption edge, while the optical transmission spectra are not so sensitive. The limiting value of the short-circuit current density for the films with different PbI2 and CH3NH3I ratios has been determined. [ABSTRACT FROM AUTHOR]

A new approach to modeling the parameters of high efficiency textured silicon solar cells (SCs) has been presented. Unlike conventional optimization formalisms, our approach additionally includes such important factors as the non-radiative Auger recombination of excitons via deep impurity levels as well as electron-hole pairs recombination in the space charge region. A simple phenomenological expression offered by us earlier for the external quantum efficiency of the textured silicon solar cells with account of the photocurrent in the long-wave part of the absorption spectrum has been also used. Applying this approach, the key parameters of textured silicon SCs, namely: shortcircuit current, open-circuit voltage and photoconversion efficiency, have been theoretically determined. The proposed formalism allows calculating the thickness dependence of photoconversion efficiency, which is in good agreement with the experimental results obtained for the heterojunction SCs with the record photoconversion efficiency of 26.6%. The offered approach and the results of applying this phenomenological expression for the external quantum efficiency of the photocurrent in the long-wave part of the absorption spectrum can be used to optimize the characteristics of high efficiency textured SCs based on monocrystalline silicon. [ABSTRACT FROM AUTHOR]

The method for estimating the loss of luminescent quanta caused by reabsorption has been proposed. The method is based on the analysis of absorption and luminescence spectra of quantum dots (QDs) with different radii r̅ and dispersion of radius Δr̅. The loss was estimated for QDs of six semiconductor materials with different bulk bandgap Eg0: CdS (Eg0 = 2.42 eV), CdSe (Eg0 = 1.74 eV), CdTe (Eg0 = 1.56 eV), InP (Eg0 = 1.34 eV), InAs (Eg0 = 0.36 eV), and PbSe (Eg0 = 0.27 eV). It has been ascertained that, by changing r̅ and Δ r̅, one can find the optimal values of these parameters, for which the losses of luminescent quanta are minimal. [ABSTRACT FROM AUTHOR]

The key parameters of silicon solar cells with back contact and rear metallization (SC-BC), such as the short-circuit current, open-circuit voltage, and photoconversion efficiency are modeled theoretically. Among other recombination channels, the model accounts for the non-radiative Auger recombination assisted by the deep recombination center and recombination in the space-charge region. It has been ascertained that these mechanisms are important in the typical commercial SC-BC in the maximal-power regime. The theory has been developed for calculating the efficiency as a function of the SC-BC thickness. Experimental and theoretical data agree well between each other. In particular, the theory has been applied to model the SC-BC produced by SunPower Corp. Depending on the surface recombination velocity on the illuminated surface and on the total surface recombination velocity on the front and rear surfaces, two mechanisms determine the optimal SC-BC thickness, at which the output power reaches its maximal. The first mechanism dominates, when the efficiency exceeds 24% under the AM1.5 conditions and is related to an essential increase of photon mean free path in the textured silicon SC. The other mechanism, more pronounced in the SC-BC with the efficiency below 22%, imposes limitations on the optimal thickness due to the surface recombination on the front SC-BC surface. [ABSTRACT FROM AUTHOR]

Materials, promising for production of luminescent solar energy concentrators were considered. It is known that the silicon oxide matrix is transparent within the spectral range where Sun emits light. Up to date, the low-temperature sol-gel method for synthesizing SiO2 coatings with the simultaneous doping of the material with quantum dots (QDs) is developed. The transmission spectrum of borosilicate glasses (BK7) is narrower than that of SiO2. Typically, the doping of BK7 with the quantum dots of the group AIIBVI is carried out using the method of condensation at high temperatures, which results in a low value of the quantum yield of luminescence. Minimal losses of luminescent quanta through the leakage cone will be in the matrix of glass LASF35 022291.541, which refractive index is 2.022. In the research of the properties of photoconductors with a luminescent concentrator, the matrix is most often made of polymethylmethacrylate (PMMA). Its doping with QDs and dyes is well developed. The quantum yield of luminescence of luminophores when doping PMMA with dyes and QDs is close to unity. The magnitude of losses of luminescent quanta in matrices of glass, PMMA and silica has been estimated. Dependence of these losses in the wave range, which should be taken into account in the study of stacked fluorescent concentrators, has been analyzed. [ABSTRACT FROM AUTHOR]

We have investigated the influence of the average radius r and its dispersion Δr¯ of the semiconductor quantum dots (QDs) used in luminescent solar concentrators (LSCs) on reabsorption. To minimize the detrimental reabsorption losses in LSCs, six semiconductors used to fabricate QDs with a wide range of their bulk band gap Eg0 have been considered, specifically: CdS (Eg0 = 2.42 eV), CdSe, (Eg0 = 1.67 eV), CdTe (Eg0 = 1.5 eV), InP (Eg0 = 1.27 eV), InAs (Eg0 = 0.355 eV), and PbSe (Eg0 = 0.27 eV). Altering r¯ and Δr, we can determine the optimal size r¯ for minimal reabsorption. As it was shown, decreasing the semiconductor bulk band gap from 2.42 down to 1.24 eV we can get such optimum QD size r that reabsorption reduces even below the combined experimental error in determination of the absorption coefficient and luminescence intensity. Further reduction of the gap Eg0, however, increases reabsorption at any values of r¯ and Δr¯: for instance, for PbSe-based QDs of 1-nm radius and dispersion of 1%, reabsorption reaches 54%. [ABSTRACT FROM AUTHOR]

This review is devoted to presentation and analysis of physical mechanisms of ohmic contacts formation in semiconductors. In addition to the classical mechanisms known for decades, new mechanisms for current flow in ohmic contacts researched for the recent decade are described. Used in this review were the original results of the authors, which they described earlier in various papers of recent years. Current flow through dislocations combined with metal shunts, realized, in particular, on the lapped semiconductor surface; detailed current flow mechanism in the presence of doping step and current flow through the heavily doped semiconductor surface charge states reduction should be noted among the new mechanisms of current flow. These current flow mechanisms are characterized by the presence of specific contact resistance growth with temperature increase in some temperature intervals and contacts ohmicity up to helium temperatures. [ABSTRACT FROM AUTHOR]

Kinetics and temperature dependence of photoconductivity were measured in macroporous silicon at 80...300 K after light illumination with the wavelength 0.9 µm. The influence of mechanisms of the charge carrier transport through the macropore surface barrier on the kinetics of photoconductivity at various temperatures was investigated. The kinetics of photoconductivity distribution in macroporous silicon and Si substrate has been calculated using the finite-difference time-domain method. The maximum of photoconductivity has been found both in the layer of macroporous silicon and in the monocrystalline substrate. The kinetics of photoconductivity distribution in macroporous silicon showed rapid relaxation of the photoconductivity maximum in the layer of macroporous silicon and slow relaxation of it in the monocrystalline substrate. [ABSTRACT FROM AUTHOR]

The influence of non-radiative exciton recombination (NRER) on the photoconversion efficiency in silicon solar cells with short Shockley-Read-Hall lifetimes tSRH has been studied. It has been shown that the efficiency reduction due to this effect is the stronger the shorter tSRH. The influence of NRER is most evident when the NRER time becomes shorter than tSRH. At sufficiently short tSRH, NRER substantially limits the optimal base doping levels of silicon solar cells, at which the photoconversion efficiency is maximal. [ABSTRACT FROM AUTHOR]

By comparison of the experimental dependence of bulk lifetime in silicon on the doping and excitation levels with theoretical calculations, it has been shown that a new recombination channel becomes operative when Shockley-Read-Hall lifetime is below 20 ms and the density of doping impurities or the excess electron-hole pair density is of the order of 1016 cm-3. This recombination mechanism is related to the non-radiative exciton Auger recombination assisted by the deep impurities in the bulk. The influence of non-radiative exciton recombination on the photoconversion efficiency in solar cells has been analyzed. It has been shown that the shorter the Shockley-Read-Hall lifetime, tSHR, the stronger its effect. In particular, for tSHR = 100 µs, this recombination channel leads to the reduction of the photoconversion efficiency by 5.5%. [ABSTRACT FROM AUTHOR]

The method of electrophysical diagnostic of n+-n-n+ structures at the etching stage of manufacturing process of power IMPATT diodes has been proposed. A numerical method for specific contacts resistance calculation of vertical ohmic contacts with a non-uniform doping level has been developed. Vertical ohmic contacts Au-Ti- Pd-n+-n-n+-Si both before and after etching were used for experimental checking this model. It has been computed the value of contact resistance in the interface metal-n+ with correction of contribution of n+-n and n-n+ resistances to the total resistance. The values of total effective resistances of vertical ohmic contacts Au-Ti-Pd-n+-n-n+-Si may be calculated using the Cox-Strack method. We used solutions of Laplace's equation for computation of specific contact resistance metal-n+ without contribution of interfaces n+-n and n-n+. The values of specific contact resistance were ~10-6 Ohm·cm². This method allows to control the manufacture process by monitoring the changes in electrophysical properties of the structure between etching cycles. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

The theoretical analysis of photovoltaic conversion efficiency of highly effective silicon solar cells (SC) has been performed for n-type and p-type bases. Considered here is the case when the Shockley-Read-Hall recombination in the silicon bulk is determined by the deep level of Fe. It has shown that, due to asymmetry of recombination parameters inherent to this level, the photovoltaic conversion efficiency is increased in SC with the n-type base and decreased in SC with the p-type base with the increase in doping. Two approximations for the band-to-band Auger recombination lifetime dependence on the base doping level are considered when performing the analysis. The experimental results are presented for the key characteristics of SC based on a-Si:H-n-Si heterojunctions with intrinsic thin layer (HIT). A comparison between the experimental and calculated values of the HIT cell characteristics has been made. The surface recombination velocity and series resistance are determined from it with a complete coincidence of the experimental and calculated SC parameters' values. Apart from the key characteristics of SC, surface recombination rate and series resistance were determined from the results of this comparison, in full agreement with the experimental findings. [ABSTRACT FROM AUTHOR]

This paper describes the results of comparative studies of illumination currentvoltage characteristics and spectral characteristics of silicon solar cells with rear location of the collector p-n-junction for the cases of non-passivated and passivated front illuminated surface. Passivation was performed by silicon dioxide layer or ITO layer. It was found that ITO layer surface passivation with formation of ITO/silicon heterojunction, unlike silicon dioxide layer passivation, leads to a significant reduction of the effective surface recombination velocity. It significantly increases the value of the internal quantum efficiency in the wavelength range from 550 to 1050 nm and, as a result, significantly increases the value of short-circuit current of solar cells. [ABSTRACT FROM AUTHOR]

Presented in this paper are experimental data on structural properties of contact metallization and temperature dependence of the specific contact resistance for ohmic contacts Au-Ti-Pd-n+-InP and Au-Ti-Ge-Pd-n+-InP prepared using the method of successive thermal evaporation of metals in oil-free vacuum in one process cycle onto the n+-n-n++-n+++-InP epitaxial structure heated to 300 °C. It has been theoretically and experimentally shown that within the temperature range 250...380 K the current transport mechanism in the ohmic contacts Au-Ti-Pd-n+-InP is thermal-field one, and in the ohmic contacts Au-Ti-Ge-Pd-n+-InP it is caused by conductivity along metal shunts linked with dislocations. According to the X-ray diffraction data, the density of these dislocations in the near-contact InP area is ~109 cm-2. [ABSTRACT FROM AUTHOR]

Characteristics of basic silicon solar cells are experimentally researched and theoretically modeled using photons of incandescent lamps as sunlight simulator. It was established that increasing temperature evokes significant acceleration of short-circuit current growth. The reason of it is the shift of simulator spectrum to the higher wavelengths region as compared to the Sun one. This effect leads to a reduction in efficiency decrease for simulated sunlight with the increase of temperature. It should be taken into account in efficiency loss calculation with increase in the operating temperature. It has been shown that the results of theoretical modeling the temperature dependences for the short-circuit current density, open-circuit voltage and photoconversion efficiency are in good agreement with the experimental data obtained using the sunlight simulator. These results could be used to develop methods for investigation of temperature dependences of solar cell characteristics by using various sunlight simulators. [ABSTRACT FROM AUTHOR]

Experimental data on manufacturing the ohmic contacts Au-Ti-Pd-n+-InP, formed using vacuum deposition of metal onto a heated to 300 °C substrate representing an epitaxial n+-n-n++-n+++-InP structure. The specific contact resistance measured at room temperature was about 7·10-5 Ohm·cm². Voltage-current characteristics within the temperature range 110 to 380 K are linear. Gunn diodes with such contacts, which were made as a straight mesa-structure in a pulsed mode (pulse duration of 100 ns, pulse ratio of 1000, operating current of 2.2 A), generated the microwave power ~10 mW in the V-band. [ABSTRACT FROM AUTHOR]

We analyzed self-consistently photoconversion efficiency of direct-gap A³B5 semiconductors based solar cells and optimized their main physical characteristics. Using gallium arsenide (GaAs) as an example and new efficient optimization formalism, we demonstrated that commonly accepted light re-emission and reabsorption in solar cells in technologically produced GaAs (in particular, with solid- or liquid-phase epitaxy) are not the main factors responsible for high photoconversion efficiency. As we proved instead, the doping level of the base material and its doping type as well as Shockley-Read-Hall and surface recombination velocities are much more important factors responsible for this photoconversion. We found that the maximum photoconversion efficiency (about 27% for AM1.5 conditions) in GaAs with typical parameters of recombination centers can be reached for p-type base doped at 2 ⋅ 1017 cm-3. The open-circuit voltage VOC formation features are analyzed. The optimization provides a significant increase in VOC and the limiting photoconversion efficiency close to 30%. The approach of this research allows to predict the expected solar cell (for both direct- and indirect-gap semiconductor) characteristics, if material parameters are known. The applied formalism allows to analyze and to optimize mass production of both tandem solar cell and one-junction SC parameters. [ABSTRACT FROM AUTHOR]

We present both theoretical and experimental temperature dependences of contact resistivity ρc(T) for ohmic contacts to the silicon n+-n-structures whose n+-layer was formed using phosphorus diffusion or ion implantation. The ρc(T) dependence was measured in the 125-375 K temperature range with the transmission line method, with allowance made for conduction in both the n+-layer and n+-n doping step. [ABSTRACT FROM AUTHOR]

Investigated in this paper are theoretical and experimental spectral dependences of the short-circuit current as well as small-signal photo-e.m.f. in silicon solar cells. The authors have considered two constructions of solar cells. The first construction is a solar cell with contacts on the front and back surfaces, and the second -- solar cells with back barriers and contact metallization. Analyzed in the work are spectral dependences of the internal quantum efficiency for the short-circuit current and smallsignal photo-e.m.f. It has been shown that the short-wave drop of the short-circuit current is related with recombination on deep centers at the front surface as well as inter-band Auger recombination in the heavily doped emitter. At the same time, availability of the shortwave drop in the small-signal photo-e.m.f. is related with limitation of the efficient rate of surface recombination Seff(λ) due to diffusion inflow. The latter takes place when a layer with the thickness dp and increased recombination is available near illuminated surface. In this case, the mechanism providing decrease in the small-signal photo-e.m.f. in the area of strong light absorption is related with increasing the efficient rate of surface recombination near the front surface, when the dominant amount of electro-hole pairs is generated in the layer with the increased recombination rate. The same mechanism is responsible for the short-circuit current drop in solar cells with back barriers and contact metallization. Juxtaposition of theoretical and experimental results enabled to determine parameters that characterize sub-surface properties of solar cells, namely: the thickness of the surface layer with increased recombination, lifetime of carriers in it, and dependences Seff(λ) . [ABSTRACT FROM AUTHOR]