A joint thermal–electrical analysis of void formation effects on concentrator silicon solar cells solder layer

It is known that the formation of voids in solar cell solder joints leads to a worsening of their heat sinking capabilities, causing an increase in the average device temperature and thermal resistance. This phenomenon can be detrimental for the solar cellʹs performance, since the open-circuit voltage linearly decreases with temperature. The performances of silicon solar cells, in the presence of voids in the cell solder joint, are studied by means of numerical simulations and of an analytical thermal model which can assess the local temperature increase at cell surface due to a single isolated void in the solder joint. The results show that for small isolated voids the analytical model gives temperature peaks above the voids which match very well with the simulations result, within 5% of relative error. The analytical model also gives an estimation of the whole device thermal resistance, in the presence of a regular pattern of non-interacting voids all with the same surface area. For a 10×7 pattern of small area voids the analytical value for the device thermal resistance matches well with the results of numerical simulations, with a maximum error of 17.3% at 70% void coverage. To determine the temperature profile of the device surface we have implemented a thermal finite element analysis (FEA) which employs a detailed 3D model of the real morphology of voids in the solar cell, obtained by X-ray inspection. The resulting temperature map has been used as an input parameter for the subsequent electrical simulations performed by means of PSPICE software, which is based on a distributed 2.5 D electrical model of the solar cell. Results show that, for a concentrating factor of 100×, a real void pattern with 36.6% void coverage does not noticeably affect the performances of a concentrator silicon solar cell.