Adel Ben Arab

Effect of the interface states on the cell parameters of a thin film quasi-monocrystalline porous silicon as an active layer

Unlike crystalline silicon, quasi-monocrystalline porous silicon (QMPS) layers have a top surface with small voids in the body. What is more pertinent to the present study is the fact that, at a given wavelength of interest for solar cells, these layers are often reported, in the literature, to have a higher absorption coefficient than crystalline silicon. The present study builds on existing literature, suggesting an analytical model that simulates the performance of an elementary thin QMPS (as an active layer) solar cell. Accordingly, the effects that the interface states located at the void-silicon interface and that the porosity of this material have on the cell parameters are investigated. Furthermore, the effects of the optimum base doping, QMPS thickness, and porosity on the photovoltaic parameters were taken into consideration. The results show that the optimum base doping depends on the QMPS thickness and porosity. For an 8@mm thickness, the film QMPS layer gives a 35.4mA/cm^2 for short-circuit current density, 15% for conversion efficiency, and 527mV for open-circuit voltage when the value of the interface states is about 10^1^2cm^-^2 and the base doping is about 2x10^1^8cm^-^3 under AM 1.5 conditions.

Analytical solutions for the photocurrent and dark diffusion current of preferentially doped polysilicon solar cells

Abstract 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%.

An accurate solution for the dark diffusion current of preferentially doped polysilicon solar cells

Abstract The total dark diffusion current of a preferentially doped polysilicon solar cell along the grain boundaries cannot be derived easily. Using the Greens 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%.

Modeling of the recombination at grain boundaries in preferentially doped polysilicon solar cells

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.

Photovoltaic properties and high efficiency of preferentially doped polysilicon solar cells

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.