W. Sinke

A new method for the evaluation of solar cell parameters

Abstract A new method is presented that is capable of resolving the parameters in a double-exponential model with which the electrical characteristics of a crystalline-silicon solar cell are analysed. This method gives not only open-circuit voltage, short-circuit current, fill factor and efficiency, but also diode saturation currents, light-generated current, series resistance and shunt resistance, all from one measurement under AM 1 illimination. The experimental set-up used for I-V measurement and automated data handling is described. A fast computer fit procedure is introduced which resolves all parameters from one measurement. The errors in the parameter values obtained are studied. A comparison of these values for a number of I-V measurements of solar cells with different internal physical properties is given, in order to illustrate the utility of the method for unravelling various electrical processes in a solar cell.

Defects in amorphous silicon probed by subpicosecond photocarrier dynamics

The photocarrier dynamics in pure nonhydrogenated amorphous silicon (a‐Si) have been studied with subpicosecond resolution using pump‐probe reflectivity measurements. The photocarrier lifetime increases with the annealing temperature from 1 ps for as‐implanted a‐Si to 11 ps for a‐Si annealed at 500 °C. The lifetime in annealed a‐Si can be returned to the as‐implanted level by ion irradiation. These observations indicate that a‐Si can accommodate a variable number of defect‐related trapping and recombination centers. The saturated defect density in as‐implanted a‐Si is estimated to be ≊1.6 at. %. Comparison with Raman spectroscopy suggests that various kinds of structural defects are present in a‐Si.

Lateral and depth distribution of hydrogen in poly-crystalline silicon for application in solar cells

The use of hydrogen as passivator in silicon solar cells is well known. The function of hydrogen is to occupy the dangling bonds in silicon that occur at defects, such as dislocations and grain boundaries. In this study we used the micro-ERDA (Elastic Recoil Detection Analysis) technique to determine the lateral and depth distribution of hydrogen in poly-crystalline silicon solar cell material. To discriminate against atmospheric hydrogen contamination, the solar cells were manufactured with deuterium as passivation. The ability of ERDA, using 4He as primary ions, to discriminate between hydrogen and deuterium signals enabled us to study the location of both passivation deuterium and atmospheric hydrogen. Within the spatial resolution of the technique, the distribution of deuterium was found not to peak at the grain boundaries, but to be homogeneously distributed in the grains, although some grains did tend to have higher concentrations of deuterium than others.

A comparison between excimer laser and thermal annealing for ion-implanted polycrystalline silicon solar cells

Abstract Polycrystalline silicon (Wacker-SILSO) solar cells have been made by phosphorous implantation in combination with pulsed excimer laser annealing or thermal annealing. It was found that laser annealing yields cells with a short-circuit current which is 3% – 4% higher than that obtained by thermal annealing, whereas the open-circuit voltage is the same for both cases. It was concluded from curve fitting that the current-voltage characteristics of all cells could be described well using a double-exponential model.

Improved Short-Circuit Current of Ion-Implanted Crystalline Silicon Solar Cells

Poly-crystalline silicon solar cells have been prepared by phosphor implantation in combination with pulsed excimer-laser annealing or thermal annealing. From a comparison between the “cold” laser processed cells and the thermally processed cells it is concluded that the base electrical properties are conserved when laser annealing is employed. This results in a short-circuit current which is 4% higher for laser processed cells than for thermally processed cells.

Optimization of Polycrystalline Silicon Solar Cells Produced by Ion-Implantation and Pulsed Laser Annealing

Silicon solar cells have been made by shallow, mass-analyzed ion-beam implantation followed by Q-switched ruby laser annealing. The influence of surface texture of the 3″ single-crystalline (100) substrates and of a thermal treatment at 400°C during 40 min. either prior to, during or after pulsed annealing on the performance of the cells has been studied. Structure and composition of implanted and annealed silicon have been investigated by RBS and channeling. Solar cell performance was charac5erized by measuring the I-V curve. In general, cutting the 45 × 45 mm2 center part out of the 3″ wafers gave improved results. Both the FF and Voc are superior in case of pulsed laser annealing of heated substrates. In contrast to earlier results on polished wafers, the etched wafers showed metallization problems which are associated with the combination of screen printing and sintering on the rather shallow p-n junctions made here. Best results, 12.7% AMI efficiency, were obtained on wafers with pyramide-shape surface texture.