Ninel Bordin

PV module power gain due to bifacial design. Preliminary experimental and simulation data

Tests and subsequent simulation are needed for rational use of bifacial instead of traditional mono facial modules for generation of additional energy. Outdoor measurements of bifacial modules were undertaken at Jerusalem (∼32 deg. of North altitude). Method of determining nominal electrical parameters (Isc and Pmax) for each side of the module is proposed. The relationships of back module irradiance and Isc, Pmax generation are studied for different climatic and design conditions: diffusion/global ratio of sun illumination, seasonal sun position, module elevation above the mounting surface, tilt panel angle, and reflectance of the underlying surface. Non uniformity of back illumination and module elevation are among factors dramatically affecting the energy gain when using bifacial modules.

Significance of bias light spectral composition for accurate measurement of silicon solar cell spectral response

To determine solar cell spectral response (SR) at working illumination conditions, measurements of the signal generated by a modulated spectral beam imposed on a DC short circuit current due to white light bias with different irradiances are typically used. In practice the bias light source does not usually simulate the suns spectrum. However the effect of the spectral composition of the bias light on the SR measurements is not known. The goal of this work is to find empirical evidence of the effect of the bias light spectrum on measured Si solar cell SR. The bifacial solar cell samples used for this study can be characterized by: significant dependence of SR on injection level, and different spatial distribution of bulk recombination centers. The sources of bias light were chosen based on their spectral composition which controls the depth distribution of carriers generation during SR measurements. An incandescent halogen lamp with a variable power supply voltage with/without optical neutral filters and ∼ 617 nm light emitting diodes were used. As the measurements show, the spectrum of the white bias light emitted by a tungsten filament of color temperature in the range 2400 – 3900 K is not a critical factor in SR measurements. However, use of highly absorbed bias light can result in a different SR compared to that measured with white light bias.

Recombination Parameters of Si Solar Cells with Back Surface Field Formed by ION Implantation

Solar cells of 1 Omegacm FZ p-Si with an n⁺-p-p⁺ structure were fabricated using combined thermal diffusion/ion implantation processing. The solar cell fabrication technology under investigation is based on the implantation of 30 keV B ions for back p ⁺ layer formation, P gas phase thermal diffusion for emitter formation, and defect annealing with simultaneous drive-in thermal treatment. The effect of the p⁺ layer formation on recombination in the solar cell base region was studied. Recombination effects due to back ion implantation were determined by analysis of back IQE, using a model of step-wise defect distribution in the base region. After implantation of 3.1middot10¹⁵-6.3middot10¹⁵ cm^-2 of B ions and subsequent annealing at 950 degC effective surface recombination, S_eff2 at the inner interface of the implanted p⁺ layer was in the range 25-60 cm/s. Formation of a defect layer of 0.5-0.6 mum adjoining the p⁺ layer was discovered, and S_eff1, at the inner interface of the defect layer is between 970-1080 cm/s. S_eff1 due to this defect layer is responsible for ~1/2 of a solar cell reverse saturation current calculated for a cell with open circuit voltage exceeding 630 mV. Non optimized combined thermal diffusion/ion implantation processing yields n⁺-p-p⁺ solar cells with efficiencies in the 19-20% range

Outdoor evaluation of power output improvement of the bifacial module

Comparative outdoor measurements of bifacial and monofacial modules were undertaken. Modules were installed in fixed positions. First, south oriented at 30° to the horizon — stand-alone and in a solar field system. The second vertically at different azimuth orientations. To separate the effects which are not connected with the rear photo response but can cause differences in energy generation gain, additional measurements were undertaken: efficiency dependence on irradiance, angular dependence of module short circuit current, and temperature coefficient of power. The energy gain for a stand-alone south oriented at 30° module exceeds 20 % at underlying surface albedo ∼50 %. It is ∼5 % higher than for the same module in a solar field where the rear contribution is affected by roof shadowing due to neighboring modules. Vertical bifacial modules with different azimuth orientation always generate significantly more energy than mono-facial modules with the same orientation.

A novel method for determining bulk diffusion length in bifacial silicon solar cells

In contrast with the usual methods using Q(/spl lambda/) with back illumination to determine the bulk diffusion length L in bifacial solar cells, the proposed method determines the actual parameters of the back doped layer and also an absolute, not differential L which is usually dependant on irradiance level. The experimental data needed are: Q(/spl lambda/) measured at low irradiance, and I/sub sc/, measured at high irradiance of known spectral distribution. The essence of the method is the determination at low irradiance of the recombination parameters of the base region and the back doped layer by comparison of calculated and experimental Q(/spl lambda/) data and use of these parameters (except L) with L as a variable to calculate Q(/spl lambda/) at high irradiance. The agreement of the measured I/sub sc/ and that calculated by integration of Q(/spl lambda/) over the light spectrum yields the correct value of L.

The JCT buried BSF silicon solar cell a model of simplicity and high efficiency

The term BSF is defined as an electric field region created by diffusion of a dopant of the same type as present in the base region of a solar cell into the back surface of the cell. The buried BSF is then defined as a BSF buried beneath a heavily doped, multicrystalline, silicon-silicon oxide layer. A simple process for fabricating a buried BSF and an optimum emitter for an n/sup +/, p, p/sup +/ silicon solar cell is described. The buried BSF, at present, provides 0.63 volt Voc, under AM1 illumination, and 1000 /spl mu/m base minority carrier diffusion length when made in 100 ohm cm silicon. An attempt is being made to utilize the buried BSF to achieve a useful high efficiency cell, possessing long term reliability and acceptable manufacturing cost.