This article provides a theoretical investigation of recombination at grain boundaries in both bulk and p-n junction regions of silicon solar cells. Previous models of grain boundaries and grain boundary properties are reviewed. A two dimensional numerical model of grain boundary recombination is presented. This numerical model is compared to existing analytical models of grain boundary recombination within both bulk and p-n junction regions of silicon solar cells. This analysis shows that, under some conditions, existing models poorly predict the recombination current at grain boundaries. Within bulk regions of a device, the effective surface recombination velocity at grain boundaries is overestimated in cases where the region around the grain boundary is not fully depleted of majority carriers. For vertical grain boundaries (columnar grains), existing models are shown to underestimate the recombination current within p-n junction depletion regions. This current has an ideality factor of about 1.8. An improved analytical model for grain boundary recombination within the p-n junction depletion region is presented. This model considers the effect of the grain boundary charge on the electric field within the p-n junction depletion region. The grain boundary charge reduces the p-n junction electric field, at the grain boundary, enhancing recombination in this region. This model is in agreement with the numerical results over a wide range of grain boundary recombination rates. In extreme cases, however, the region of enhanced, high ideality factor recombination can extend well outside the p-n junction depletion region. This leads to a breakdown of analytical models for both bulk and p-n junction recombination, necessitating the use of the numerical model.

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The parallel multi‐junction solar cell design has recently been proposed to reduce the costs of photovoltaics, while maintaining or improving device performance. This design uses alternating layers of n‐ and p‐type semiconductor to ensure that every point in the device is much less than one diffusion length from a collecting junction, producing relatively high currents. Device voltages can be maintained through heavier doping than would normally be used. This approach is particularly suited to very low‐quality material where the diffusion lengths are much shorter than the device thickess required for significant photogeneration. In particular, this design strategy is seen as a way to realize the potential of thin‐film polycrystalline silicon solar cells for large‐scale, cost‐effective energy generation. A brief description of the parallel multi‐junction solar cell is presented, along with some analysis where parallel multi‐junction solar cells differ from conventional cells. Results from an analytical one‐dimensional model and two‐dimensional numerical simulations are presented, highlighting some of the significant advantages of parallel multi‐junction solar cells.

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The multilayer cell has been specifically designed with the aim to obtain high solar cell efficiency using low quality, thin film, polycrystalline silicon material. The structure consists of multiple p-and n-type silicon layers. This paper examines the tolerance of the cell design to a range of metallic impurities and grain boundaries using computer simulations. The modelled results indicate that the device can tolerate impurity concentrations up to 250 times greater than a conventional, thick solar cell. Further, the results indicate that the structure has excellent tolerance to grain boundaries present in bulk regions of the device. The simulations indicate that grain boundaries present in depletion regions will limit efficiencies considerably if the effective recombination velocity of the grain boundary approaches 10 % cm/s. This extreme case should be largely avoided utilizing grain boundary passivation techniques during device fabrication.