Search

Sufficiently deep local back-surface-fields (LBSF) are crucial for achieving low contact recombination and thus high solar cell efficiencies in passivated emitter and rear contact (PERC) solar cells. In this article, we investigate spatial variations of LBSF thickness 1) across dashed contacts, 2) between lateral positions within a cell, and 3) from cell to cell. The objective of this experimental study is to proof the impact of LBSF thickness on open-circuit voltage in PERC solar cells. Our measurements and analysis of variance (ANOVA) reveal that variations in LBSF thickness across dashed contacts exceed observed variations in LBSF thickness between lateral positions within a cell as well as cell-to-cell variations. Thus, we statistically treat all LBSF measurements of a single experimental group of PERC solar cells as one population of measurements. The two investigated experimental sets of PERC cells fired using different fast-firing profiles show a difference in LBSF thickness of about 1 μm. The resulting difference in open-circuit voltages arises to 1.3 mV. ANOVA-based analysis shows for our experimental samples that at least 19 random measurements are necessary in order to resolve LBSF thickness difference of 0.5 μm with sufficient statistical significance.

We present an evaluation of the silicon solar cell as well as the photovoltaic (PV) module size and its effect on thermomechanical stress. The evaluation is based on finite-element method (FEM) simulations. Within these simulations, we perform parameter variations of the number of solar cells within a PV module from 60-140 cells, of the cell size from 156.0-161.75 mm, and the cell format from full cells down to quarter cells. The FEM simulations cover the lamination process, mechanical load, and thermal cycling for glass-foil as well as glass-glass modules. The presented results reveal correlations between the solar cell and module size with the stress in the solar cells. We also find that the interaction of the laminate with the module frame plays a significant role in thermal cycling. Of the varitations under investigation, the increase in cell size has the largest effect on the stress. However, at a mechanical load of 2400 Pa, glass-foil modules with less than 96 solar cells have a negligible failure probability. The advantage of placing the solar cells in the neutral axis of the laminate is proven by the negligible tensile stress values for all variations of the glass-glass modules.

Many manufacturers choose the passivated emitter and rear cell (PERC) approach in order to surpass the 20% cell efficiency level in mass production. In this paper, we study the efficiency potential of the PERC approach under realistic assumptions for incremental improvements of existing technologies by device simulations. Based on the most recent published experimental results, we find that the PERC structure is able to reach about 24% cell efficiency in mass production by an ongoing sequence of incremental improvements. As a guideline for future developments, we provide a method to improve cell efficiency most effectively by monitoring the current losses at the maximum power point. By means of numerical device modeling, we identify some key technologies toward 24% efficient PERC cells and provide its technology-related target requirements.

This work aims to improve the rear-side properties of p -type monocrystalline silicon solar cells by using the passivated emitter and rear locally diffused (PERL) solar cell concept. To realize the rear side structure, the so-called PassDop approach was used combining both surface passivation and local doping. The concept utilizes a multifunctional, doped AlO x /SiN x :B layer stack; the localized structuring is achieved by local contact opening and doping by a laser process. Using AlO x /SiN x :B PassDop layers, an outstanding effective surface recombination velocity S eff of less than 4 cm/s was achieved after firing at the passivated area. The boron concentration in the PassDop layers did not show any significant influence on S eff . Laser doping resulted in highly doped regions in the silicon with a sheet resistance of below 20 Ω/sq and surface doping concentrations close to 1 × 1020 cm–3. Accordingly, calculations showed that the saturation current density at the laser doped areas can be as low as 900 fA/cm² for line-shaped contact structures.