Amorphous Submicron Layer in Depletion Region: New Approach to Increase the Silicon Solar Cell Efficiency

Abstract

The insertion of a thin amorphized layer (AL) in the space charge region of a silicon solar cell is proposed as a way to improve the conversion efficiency due to the impurity photovoltaic effect. Previously, this approach had been applied to a cell with a layer inserted in the emitter by the ion implantation. The insertion of such layer in the space charge region is founded to be preferable, because a better control over the recombination (via energy levels in the band gap and local states of interfaces) can be achieved. The parameters of a modified device are investigated by the numerical simulation, and it is concluded that the layer parameters have a crucial influence on the cell conversion efficiency. Based on our simulation results, the optimal AL and the height of barriers are determined. In such a case, the short circuit current density is improved due to the absorption of photons with energy less than a silicon band gap of 1.12 eV in AL, whereas the open circuit voltage and fill factor remain unchanged. Theoretically, the increase in the efficiency by 1–2% is achievable. In the non-optimal case, the degradation of a short circuit current and the fill factor eliminate the positive effect of an additional photogeneration in AL.