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Boron and phosphorus doping of crystalline silicon using a borosilicate glass (BSG) layer from plasma-enhanced chemical vapor deposition (PECVD) and phosphorus oxychloride diffusion, respectively, is investigated. More specifically, the simultaneous and interacting diffusion of both elements through the BSG layer into the silicon substrate is characterized in depth. We show that an overlying BSG layer does not prevent the formation of a phosphorus emitter in silicon substrates during phosphorus diffusion. In fact, a BSG layer can even enhance the uptake of phosphorus into a silicon substrate compared with a bare substrate.From the understanding of the joint diffusion of boron and phosphorus through a BSG layer into a silicon substrate, a model is developed to illustrate the correlation of the concentration-dependent diffusivities and the emerging diffusion profiles of boron and phosphorus. Here, the in-diffusion of the dopants during diverse doping processes is reproduced by the use of known concentration dependences of the diffusivities in an integrated model. The simulated processes include a BSG drive-in step in an inert and in a phosphorus-containing atmosphere.Based on these findings, a PECVD BSG/capping layer structure is developed, which forms three different n++−, n+− and p+−doped regions during one single high temperature process. Such engineered structure can be used to produce back contact solar cells. published

26th European Photovoltaic Solar Energy Conference and Exhibition; 1160-1163, Applying the standard process for p-type solar cells to n-type silicon results in a “PhosTop” solar cell with a screen printed alloyed aluminum emitter on the rear side [1]. This cell concept can be improved by adding a selective FSF and a SiO2/PECVD SiNx stack passivation layer, resulting in a highest confirmed stable efficiency of 19.4 % for 6” n-type Cz-Si solar cells [2]. Besides a very low front SRV, this cell concept also demands for a very high bulk lifetime. We therefore analyze the change of bulk lifetime and conductivity after each high temperature process step in the applied cell process. Furthermore we investigate the current generation from the unprinted wafer edge with no emitter.

Um die Rückseitenpassivierung von siebgedruckten bifacialen Solarzellen zu verbessern, wurde im Rahmen dieser Arbeit die Qualität der Passivierungsschicht dieser Solarzellen in Abhängigkeit ihrer wesentlichen Eigenschaften charakterisiert. Weiter wurden verschiedene Rückseiten-Passivierungen bei der Herstellung von bifacialen Solarzellen realisiert und die hergestellten Solarzellen im Hinblick auf ihre Rückseitenpassivierung charakterisiert.

24th European Photovoltaic Solar Energy Conference, 21-25 September 2009, Hamburg, Germany; 1596-1599, The aim of the work is the comparison of large area Cz-Si solar cells with boron back surface field (B-BSF) to those with full area aluminum (Al) BSF. The investigations are carried out with respect to the influence of the wafer thickness on the cell performance. Boron doped Cz-Si wafers of varying thickness (115-240 μm) are used as bulk material. The B-BSF is formed by BBr3-diffusion. Metallization is applied via screen printing a grid on the front and rear side. Full area aluminum BSF solar cells are used as reference. The solar cells show high open-circuit voltages (VOC) up to 635.4 mV and short-circuit current densities (JSC) up to 36.5 mA/cm2. Neither VOC nor JSC decrease with decreasing wafer thickness. The full area Al-BSF reference solar cells show decreasing fill factors and therefore reduced cell efficiencies with decreasing wafer thickness. The cells with B-BSF reveal internal quantum efficiencies (IQEs) of 60% at 1100 nm. Going to thinner wafers, the IQE is not reduced in the long wavelength regime. The effective back surface recombination velocities (SRVs) extracted from a physical model fitted to spectral response measurements are in the range of 80-200 cm/s for the boron BSF cells. Effective back SRVs of the aluminum BSF cells are determined to 260-700 cm/s.