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The present study employs porous silicon (PS) or quasi-monocrystalline porous silicon (QMPS) as a reflector material on the rear side. It presents an analytical model that simulates the performance of n+–p–p+ thin silicon solar cell with a QMPS layer on the rear side. The development of the model involves the formulation of a complete set of equations for the photocurrent density that is then solved analytically in the base region, including the photocurrent generated under the effect of the light reflected by QMPS layer. This also takes the contribution of the back p+-region (back surface field) to the generated photocurrent into consideration. The enhancements brought by the thin film QMPS with regard to photovoltaic (PV) parameters are then investigated and compared to those brought by the conventional silicon solar cell. Moreover, the effect of the QMPS layer on the current–voltage characteristics J–V and the internal quantum efficiency (IQE) of thin silicon solar cells are simulated by means of AFORS-HET software. These simulations show that the improvement of the PV parameters is due to an increase in the transport parameters of minority carriers in the p-region.

In this paper, the high efficiency TCO-n(aSi:H)-i(aSi:H)-p(c-Si)-$$\hbox {p}^{+}$$p+(aSi:H) heterojunction with intrinsic thin-layer (HIT) solar cell is analyzed. The effects of the intrinsic thin-layer and the back surface field (BSF) on the photovoltaic parameters of thin solar cells are discussed. The analytical results show that the intrinsic layer inserted at the a-Si:H/c-Si interface decreases the density of interface states. If the interface state density is lower than $$10^{11}\,\hbox {cm}^{-2}$$1011cm-2 in the presence of an intrinsic thin layer a-Si:H, the effect of recombination current density on the photovoltaic parameters becomes low. The BSF formed by hydrogenated amorphous silicon layer can increase the conversion efficiency by about 2.6 % and the open-circuit voltage to $$\sim $$~80 mV as compared to the HIT solar cell wherein the BSF is realized by crystalline silicon. The results obtained from the simulation studies are in good agreement with the literature, and might open promising opportunities for enhancing the design parameters of HIT cells.

The present paper accounts for a simulation study carried out to determine and optimize the effect of the high---low junction emitter front surface field (FSF) of thin heterojunction solar cell $$\text {n}^{+}$$n+(a-Si: H)/n(SiGe)/p(Si)). A theoretical model describing the behavior of heterojunction $$\text {n}^{+}$$n+---n---p type solar cells has been proposed. Besides, the expression of the photovoltaic equations allowing for the obtention of the optimal quantum efficiency of the solar cells based on the suggested model has been given. The effects of the a-Si:H-layer thickness and Ge fraction are discussed, using the computed results. The main role of an FSF layer is to reduce the effect of front surface recombination and the enhancement of light-generated free carriers' collection. This is primarily responsible for the increase of the spectral response compared with the conventional solar cell. This is achieved by the drastic reduction of the effective recombination at the emitter upper boundary and the optimum value of $$\text {n}^{+}$$n+ layer thicknesses (a-Si:H) is about 2 nm.

In this paper we study the growth of SiGe thin films (n-type) on c-Si substrate (p-type) by Molecular Beam Epitaxy. High resolution Raman spectroscopy atomic force microscopy and X-ray diffraction are used to characterize the thin epitaxial layers of n-type SiGe thin films. The refractive index $$n\left( \lambda \right)$$ and the extinction coefficient $$k\left( \lambda \right)$$ of SiGe thin films with various Ge fractions are determined using spectroscopic ellipsometry in the frame of the Forouhi and Bloomer model. The simulation study shows that the refractive index decreases with Ge fraction in the U–V range whereas, the extinction coefficient increases in the visible region. The experimental extracted Eg of SiGe agrees well with the theoretical calculation on the strained SiGe material. The luminescence is characterized by a broad PL band centered at 779 nm.

The present paper reports on a simulation study carried out to determine and optimize the effect of the high–low junction emitter (n+-n) on thin silicon solar cell performance. The optimum conditions for the thickness and doping level of the front surface layer with a Gaussian profile were optimized using analytical solutions for a one dimensional model that takes on the theory relevant for highly doped regions into account. The photovoltaic parameters of silicon solar cells with front surface field layer (n+-n-p structure) and those of the conventional one (n-p structure) are compared. The results indicate that the most important role played by the front surface field layer is to enhance the collection of light-generated free carriers, which improves the efficiency of the short wavelength quantum. This is achieved by a drastic reduction in the effective recombination at the emitter upper boundary, a property primarily responsible for the decrease in the emitter dark current density. The findings also indicate that the solar cell maximum efficiency increase by about 2.38% when the surface doping level of the n+-region and its thickness are equal to 2.1020 cm−3 and 0.07 μm, respectively.

The present study developed a simple analytical model to simulate the performance of polysilicon solar cells with porous silicon (PS) layer at the backside. It analytically solved the complete set of equations necessary for the determination of the photocurrent generated under the effect of the reflected light. It also investigated the contribution of the light absorbed by the PS layer and explored the effect that the latter's number of double porosities and high porosity have had on photovoltaic parameters. The findings suggest that the photovoltaic parameters increase with the number of double porosities that the layer might have in a given structure. When the PS layer is formed by three-double porosity layers 20%/80% and for a [email protected] film c-Si, the backside reflector gives a total improvement of about 2.65mA/cm^2 in photocurrent density and 1.4% in cell efficiency. This improvement can even be of much more important for well passivated grain boundaries and back contact of solar cells.

A simple analytical model has been developed to simulate the performance of solar cells with polysilicon contact on the front surface. The polysilicon layer with a columnar grain structure is modeled by an effective recombination velocity using a two-dimensional transport equation. A one-dimensional transport equation in the single-crystal emitter is solved, taking into account bulk recombination and non-uniformly doped emitter. Then, simple analytical expressions for the emitter reverse saturation current and light-generated current densities are obtained. The collection of the light-generated carriers in polysilicon layer has been discussed and an analytical solution of the light-generated current is derived. The results show that the polysilicon layer can result in a decrease in emitter reverse saturation current density and an increase in solar cell photovoltaic parameters. In fact, the emitter region should not be treated as a ‘dead layer’ because thin polysilicon layer front surface contact gives an improvement of about 60 mV for the open-circuit voltage, 3.6 mA/cm2 for the photocurrent, and 3.9% for the cell efficiency.

In order to improve the current gain via a reduction of the emitter base junction saturation current density, a perpendicular ordering of the grain boundaries (columnar grain boundaries) in the polysilicon emitter-region of a bipolar transistor is proposed. The complex polysilicon current component is obtained by a two-dimensional resolution of the current transport equation along the polysilicon region. The minority carrier current density component in the non-uniformly heavily doped single-crystal emitter is calculated by an average value approach. The influence of the two-dimensional structure of the polysilicon region on the current gain is analysed, and it is shown that the current gain decreases with increasing grain number. The evolution of the normalised current gain in terms of physical parameters is studied. The results show that the current gain improves with polysilicon thickness for a thin oxide layer, while it is insensitive for a thick oxide layer. In addition, the results show that the bulk recombination in a single-crystal emitter cannot be neglected in devices with a deliberately grown interfacial oxide.

Making use of results developed in an earlier paper and according to the theory of Oualid et al., the photovoltaic parameters of a preferentially doped N+ P solar cell are studied as a function of the density of interface states (Nt) at the grain boundaries. The results are compared to the ones established with respect to the grain boundary recombination velocity Vs (without considering grain boundary recombination theory). The results show that in the case of small recombination at the grain boundaries (Nt < 1012 cm−2) the variation of the photovoltaic parameters with respect to the density Nt is similar to that obtained with the velocity Vg. The results also show that, when the density Nt is superior to this value, the decrease of the optimum base doping giving the maximum efficiency of the cell with respect to the grain width (in a log-log plot), is no longer linear. This result contradicts the one of Dugas and Oualid.

Making use of new solutions for the photocurrent and dark current, developed earlier, the photovoltaic properties of a preferentially doped n+p solar cell are examined taking into consideration Shockley-Read-Hall recombination, Auger recombination and heavy doping effects. Numerical calculations have been carried out for the analysis of the effects of the doping concentration, grain size, preferential doping penetration depth along the grain boundaries, and grain boundary recombination velocity on the photovoltaic parameters of the cell. The results reveal that, in order to obtain a high cell efficiency, the emitter doping level should not exceed 5 × 1019 cm−3 and the base must be doped at an optimum level. It is found that the optimum base doping depends on the grain width and grain boundary recombination velocity and is practically unchanged with preferential doping. The results also show that a conversion efficiency exceeding 20% under AM1 conditions is obtained, when the grain is preferentially doped, and when the grain boundaries and the top and back contact surface are passivated.

A two-dimensional physical model is used in the analysis of the photovoltaic properties of a preferentially doped polycrystalline silicon solar cell along the grain boundaries. The cell is assumed to have an oriented columnar structure formed by a juxtaposition of silicon grains. A mathematical analysis, based on the superposition principle and the technique of separation of variables, is presented. This analysis has allowed us to obtain analytical expressions for the photocurrents and dark diffusion currents of the horizontal junction and vertical junctions of the base region. These expressions are valid for any arbitrary value of the recombination velocity at the grain boundaries. The results show that the preferential doping significantly improves the performance of polycrystalline silicon solar cells especially in those formed by fine grains and with high recombination at the grain boundaries. In fact, with a grain size W = 20 μ m, the preferential doping makes possible an increase of 62% in the short-circuit current, a decrease in the dark diffusion current which can reach 58.5% and an enhancement in the conversion efficiency more than 3%.

The total dark diffusion current of a preferentially doped polysilicon solar cell along the grain boundaries cannot be derived easily. Using the Green's function method and the moment method, the expressions for the dark currents of the horizontal and vertical junctions of an elementary cell are well established. The preferential doping realizes vertical junctions along the grain boundaries and at the same time decreases the total dark diffusion current of the cell. Consequently, this allows an enhancement of the cell efficiency. In fact, the results show that in the case of a cell of small width ( W = 20 μm ), the preferential doping with a penetration depth of ( Z d = 15 μm ) decreases the dark diffusion current of the cell by about 63%. However, the enhancement of the cell efficiency which resulted does not exceed 0.77%.

A two-dimensional photoresponse analysis of the preferential doping efficiency in polysilicon solar cells is presented. The cell is illuminated by a rectangular light spot of width a. The short-circuit currents induced in the horizontal and vertical base region junctions are then calculated. Spectral and spatial photoresponses are used to study the preferential doping efficiency for an individual grain. These photoresponses are obtained when the beam is centered over a grain boundary and when it is displaced across the grain respectively. Curves illustrating the effects of the base region parameters such as the minority carrier diffusion length, grain width and thickness, and the state of the back contact on these photoresponses are presented. In the case of finite grain width and small recombination velocity at the back contact, the photoresponses present characteristics which are different from those established by Ragaie et al. in the case of a semi-infinite model used to study large grained polysilicon solar cells.

We propose a two-dimensional model to study the photoresponse of polysilicon solar cells. The cell is supposed to be formed by a juxtaposition of silicon grains which form an oriented columnar structure. The proposed model introduces the contribution of preferential doping (vertical junctions) realized along grain boundaries to photoresponse. Green's function method is used to solve the diffusion problem of the photogenerated carriers in the grain volume. Curves illustrating the effects of the base region parameters (geometrical and inertial) on the total photoresponse and detailed photoresponses of the different cell zones are presented. In particular, we show that the vertical and horizontal junction photoresponses are complementary and involve the same wavelength domain. An important contribution of the preferential doping to the base region photoresponse appears when the grain width is thin. In fact for a grain of width W = 20 μm this contribution is about 50%.

The present paper reports on a simulation study carried out to determine and optimize the effect of the high-low junction emitter (n+/n) of thin film SiGe/Si solar cell. The model is based on a simple analytical approach that draws on relevant device physics, including effective surface recombination velocity at the high-low junction and band discontinuities associated with heterojunctions. The collection of the light absorbed by the front surface field is discussed and an analytical solution is derived for the light-generated current in this layer. The photovoltaic parameters of SiGe/Si solar cells and those of the conventional cell Si/Si are compared. The findings revealed that the addition of Ge ~15 % to crystal Si highly enhances short-circuit current density and cell efficiency, whereas the SiGe band-gap degrades particularly the open-circuit voltage. The results also indicate that the solar cell maximum efficiency increase by about 1.7 % when the interface state density is lower than 1011 cm−2.