We investigated the bonding-related gases trapped inside the cavities of micromachined silicon test structures that had been sealed by silicon direct bonding or anodic bonding under vacuum conditions. The gas content inside the cavities was analyzed by quadruple mass spectroscopy. The magnitude of the residual gas pressure inside the cavities for different cavity layouts and for various bonding processes was monitored. In cavities bonded by low-temperature silicon direct bonding the residual gases are reaction products originating from the mating silicon surfaces during annealing.

In this work, we report on hole selective passivating contacts, which consist of a SiOx tunnel layer and an in situ boron‐doped 300 nm thick p+ polysilicon layer deposited by LPCVD. Using a SiNx:H capping layer, we show an extremely low dark saturation current density J0 of 1 fA cm−2 after contact firing. At the same time, we demonstrate that commercially available and screen‐printed fire through Ag pastes are capable of contacting the p+ polysilicon layer, with minimum contact resistance ρc = 2 mΩ cm2. We do find increased interface recombination below the metal contacts of around 250 fA cm−2, which represents a considerable advance compared to conventional screen printed metallisation on diffused junctions.

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For optimum performance of solar cells featuring a locally contacted rear surface, the metallization fraction as well as the size and distribution of the local contacts are crucial, since Ohmic and recombination losses have to be balanced. In this work we present a set of equations which enable to calculate this trade off without the need of numerical simulations. Our model combines established analytical and empirical equations to predict the energy conversion efficiency of a locally contacted device. For experimental verification, we fabricate devices from float zone silicon wafers of different resistivity using the laser fired contact technology for forming the local rear contacts. The detailed characterization of test structures enables the determination of important physical parameters, such as the surface recombination velocity at the contacted area and the spreading resistance of the contacts. Our analytical model reproduces the experimental results very well and correctly predicts the optimum contact spacing without the use of free fitting parameters. We use our model to estimate the optimum bulk resistivity for locally contacted devices fabricated from conventional Czochralski-grown silicon material. These calculations use literature values for the stable minority carrier lifetime to account for the bulk recombination caused by the formation of boron-oxygen complexes under carrier injection

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We investigate the surface recombination velocity Sp at the silicon-dielectric interface of phosphorus-doped surfaces for two industrially relevant passivation schemes for crystalline silicon solar cells. A broad range of surface dopant concentrations together with a high accuracy of evaluating the latter is achieved by incremental back-etching of the surface. The analysis of lifetime measurements and the simulation of the surface recombination consistently apply a set of well accepted models, namely, the Auger recombination by Richter et al. [Phys. Rev. B 86, 1-14 (2012)], the carrier mobility by Klaassen [Solid-State Electron. 35, 953-959 (1992); 35, 961-967 (1992)], the intrinsic carrier concentration for undoped silicon by Altermatt et al. [J. Appl. Phys. 93, 1598-1604 (2003)], and the band-gap narrowing by Schenk [J. Appl. Phys. 84, 3684-3695 (1998)]. The results show an increased Sp at textured in respect to planar surfaces. The obtained parameterizations are applicable in modern simulation tools such as EDNA [K. R. McIntosh and P. P. Altermatt, in Proceedings of the 35th IEEE Photovoltaic Specialists Conference, Honolulu, Hawaii, USA (2010), pp. 1-6], PC1Dmod [Haug et al., Sol. Energy Mater. Sol. Cells 131, 30-36 (2014)], and Sentaurus Device [Synopsys, Sentaurus TCAD, Zurich, Switzerland] as well as in the analytical solution under the assumption of local charge neutrality by Cuevas et al. [IEEE Trans. Electron Devices 40, 1181-1183 (1993)]

We present a standard p + pn + solar cell device exhibiting a full-area aluminum back surface field (BSF) and a conversion efficiency of 20.1%. The front side features a shallow emitter which has been exposed to a short oxidation step and reduces the emitter dark saturation current density j 0e to 160 fA/cm 2 on a textured surface. The front contact is formed by light-induced nickel and silver plating. Also, devices featuring screen-printed front contacts have been realized that reach a conversion efficiency of 19.8%. PC1D simulations are presented in order to extract the electronic parameters of the BSF. Therefore, external quantum efficiency and reflectance have been determined for modeling the internal quantum efficiency by adapting surface recombination and lifetime of the PC1D-simulated silicon device. As a result, a recombination velocity of S BSF = 283 cm/s and a dark saturation current density of j BSF = 274 fA/cm 2 in the Al BSF are determined. This results in an effective diffusion length L eff = 1150 μm.