18.4% Efficient Grid Optimized Cells With 100-Ω/sq Emitter

An optimized front-grid design with fine-line fingers allows efficiency η ≈ 18.4%, for industrial c-Si solar cells with homogeneously doped emitter of sheet resistance R_sh = 100 Ω/sq. An additional gain Δ η_gain,bb ≈ 0.5% in efficiency is expected by using a grid of busbars instead of the standard H-pattern front grid. We apply a new method to optimize the front-grid design by minimizing the optical, electronic, and electrical losses of the metallization. The “remove, design, optimize” (ReDO) method theoretically removes the existing contact grid, calculates the ideal efficiency η* without any front-side losses as a goal, designs new front grids for the particular cell, and selects the optimum design for a maximum efficiency η. Starting from the experimentally measured performance of a real solar cell, the ReDO method predicts η of the cell, by considering the dependence of the current J_mpp and the voltage V_mpp at the maximum power point on the front-side losses, enabling a precise efficiency loss analysis.