High-performance Silicon Solar Cells Research Articles

Optimization of the high-performance multi-crystalline silicon solidification process by insulation partition design using transient global simulations

A transient global model was established to investigate the effect of the raise velocities of the partition block on the crystal growth rate, the crystal–melt (C–M) interface and the thermal stress distribution during the solidification process. The simulation results showed that among the different raise velocities of the partition block, initially slowly raising and then rapidly raising the partition block was the most favorable for the solidification process. A slightly convex C–M interface and low thermal stress distribution were obtained, and a fast crystal growth rate was also achieved. Thus, this design was implemented in casting experiments, and the experimental results indicated that this design was beneficial for optimizing the C–M interface in the solidification process. The average conversion efficiencies of high-performance multi-crystalline silicon solar cells was about 0.13% higher with this design (18.18%) than with a fixed partition block design (18.05%).

Enhanced performance of solar cells with optimized surface recombination and efficient photon capturing via anisotropic-etching of black silicon

We report an enhanced conversion efficiency of femtosecond-laser treated silicon solar cells by surface modification of anisotropic-etching. The etching improves minority carrier lifetime inside modified black silicon area substantially; moreover, after the etching, an inverted pyramids/upright pyramids mixed texture surface is obtained, which shows better photon capturing capability than that of conventional pyramid texture. Combing of these two merits, the reformed solar cells show higher conversion efficiency than that of conventional pyramid textured cells. This work presents a way for fabricating high performance silicon solar cells, which can be easily applied to mass-production.

High-performance tandem silicon solar cells on F:SnO2

High-performance transparent conducting oxides (TCOs) have significance for optimising PV performance. The efficiency of the resulting solar cells is dependent particularly on achieving high light scattering, low resistivity and low absorption (via low free carrier absorption), in addition to suitable surface morphology for absorber growth quality. These properties have been targeted by systematic exploration of the Atmospheric Pressure Chemical Vapour Deposition (APCVD) growth parameters, in particularly the effect of the tin precursor to water ratio.Using the APCVD process F-doped SnO2 has been deposited on glass using monobutyl tin trichloride with trifluoro-acetic acid as the dopant source. Experiments established that an increased water to tin precursor ratio gave smaller surface features, along with increased electrical mobility and optical transmittance at high reactant ratios. Samples were then used in manufacture of thin film solar cells, which showed enhanced performance, in comparison to commercially available TCO CVD coated glasses, with high quantum efficiency yield. In particular, high water to tin precursor ratios led to much improved open circuit voltages, fill factors and high current densities within the cells. Tandem cells with efficiencies of 10.75% were achieved, which were higher than those produced concurrently using commercially available TCO both on-line 9.50% and off-line 10.20%.

Interface engineering for the passivation of c-Si with O3-based atomic layer deposited AlOx for solar cell application

We have investigated the effects of deposition temperature and post-annealing on the passivation performance of AlOx films deposited by O3-based atomic layer deposition for crystalline Si. We found that the dramatic enhancement in the passivation performance of room-temperature deposited AlOx films by post-annealing is due to the phase transformation of aluminum silicate to mullite in an AlOx interlayer and the resulting self-aligned AlOx/SiOx interface. This result is interesting for the fabrication of high-performance silicon solar cells with AlOx passivation layers.

Analysis of sunlight loss for femtosecond laser microstructed silicon and its solar cell efficiency

Black silicon, which is obtained by irradiating the surface of a Si wafer with femtosecond laser pulses in the presence of a sulfur-bearing gas, holds great promise in the preparation of high-performance intermediate band silicon solar cells. Using a three-level model, the enhanced usefulness of sunlight of the microstructured silicon was firstly analyzed. A detailed study on the relationship between the light loss, the ionization energy of doped impurities in silicon and the impurity band width were given. Then the effect of the position of intermediate band within the forbidden gap of silicon on the theoretical conversion efficiency for the corresponding solar cell is discussed using the Detailed Balance Theory. Finally problems need to be resolved in making intermediate band solar cells based on femtosecond laser microstructured silicon are pointed out with great emphasis.

Depletion region recombination in silicon thin-film multilayer solar cells

A parallel multijunction approach appears promising as a way of producing high-performance polycrystalline thin-film silicon solar cells by deposition onto inexpensive glass superstrates. Recent independent analyses have confirmed some of the claimed advantages for this approach. However, both the size of likely advantages and the domain of parameter space over which they prevail have been underestimated in many cases. This is due to a failure to incorporate an essential design feature: tailoring of junction properties to minimize junction recombination. It is shown that insertion of thin intrinsic regions between the doped layers of the multilayer stack can reduce junction recombination significantly, by a factor of over 800 000 from values calculated in one recent study.

Global isolation at Gaborone measured at 30° tilt angle using a standardised high performance silicon solar cell

Between the period June 1991 and August 1992, the global solar irradiance on the campus of the University of Botswana at Gaborone, was monitored continuously employing a simple circuitry which incorporates a high performance silicon solar cell (HPC) as a radiometer (vide reference 8, for a preliminary report). The solar cell, a 2x2 cm 2 violet cell, was mounted inclined at 30° to the horizontal and faced north. In this paper, the variation of the mean monthly global irradiance, as measured at a tilt angle of 30° over a 12 month period will be compared with data from Sebele, a national observatory, about 10 km away, which employes a conventional thermopile radiometer mounted horizontally. The data from the experimental arrangements will also be weighed against theoretical calculations by Andringa 11. The paper concludes by establishing a high correlation between experimental and theoretical data on one hand and gives conclusive evidence for the detector angular tilt effect 9 on the other.

Computer simulation model of the effects of interface states on high-performance amorphous silicon solar cells

A computer simulation model of amorphous silicon solar cells using a Scharfetter and Gummel solution of Poisson’s equation and Taylor and Simmons occupancy statistics for the dangling bond gap states (D states), has been developed. With a suitable choice of parameters, the numerical results for solar cell collection efficiency and dark and illuminated I-V characteristics agree well with experimental values. The model has been used specifically to study the influence of interface states at the TCO-p (transparent conductive oxide), p-i, i-n, and n-metal interfaces and to explain the beneficial role of a graded-band-gap layer at the p-i interface.

Oxidation condition dependence of surface passivation in high efficiency silicon solar cells

Several recent high performance silicon solar cells have taken advantage of surface oxide passivation to improve both their short wavelength response and open-circuit voltage. Using low resistivity substrates to minimize base recombination rates, the effect of oxidation conditions upon the passifying properties of thin oxides is quantified. It is shown that emitter recombination in high efficiency cells decreases by a factor of at least 3 and most probably 7 as the oxide growth temperature increases from 825 to 900 °C and the oxide thickness increases from 60 to 100 Å. This increase in performance is at the expense of a slight loss in cell short-circuit current density.

Relationship between the blue response and open-circuit voltage of high performance silicon solar cells

The relationship between the response at blue wavelengths and the open-circuit voltage of high performance silicon solar cells with a virtually transparent emitter is analyzed. It is shown that a one-dimensional cell model cannot simultaneously model the optical collection properties and operating characteristics of such cells. The analysis highlights the importance of surface conditions and shows that previous conclusions regarding bounds on Auger coefficients imposed by correlating these parameters must be treated with caution.