Short-Circuit Current Losses in Back-Contacted Back–Junction Si Solar Cells: Experiment and Simulation of the Charge Collection Probability

Abstract

The influence of recombination losses on the short-circuit current density J <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">sc</sub> of back-contacted back-junction silicon solar cells has been investigated by experiments and simulation. The J <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">sc</sub> losses are analyzed by 2-D simulations of the charge collection probability f <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</sub> using the reciprocity theorem. For the investigations, Gaussian-like emitter, back-surface field, and front-surface field diffusion profiles, as well as a sophisticated optical model, have been applied. Thus, experimental and simulated results of solar cells with different rear-side dimensions, i.e., pitch distance, and base resistivities could be directly compared. The diffusion profiles, the bulk charge carrier lifetime, and the surface recombination velocities of the diffused regions have been determined experimentally and used as input parameters for the simulations. It has been found that the simulated results are in good agreement with the experimental ones. The measured local and global external quantum efficiency of the solar cells could be well reproduced by the simulations. Hence, the presented simulation model provides a powerful tool to adapt the rear-side dimensions and to optimize the diffusion profiles of back-contacted back-junction silicon solar cells in order to reduce recombination losses and achieve high J <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">sc</sub> values.