The Amorphous/Crystalline Silicon Interface Research of HIT Solar Cells by Simulation

Abstract

In this paper, we have focused on the influence of interface state density and band offsets on the performance of HIT solar cells by simulation. The interface state density D_it have negative influence on the open-circuit voltage V_OC, fill factor FF and the short circuit current J_SC, beyond different D_it respectively. V_OC decreases monotonically with increasing D_it only when D_it is greater than 10¹⁰ cm^-2, and for FF and J_SC D_it is 10¹² cm^-2, 10¹³ cm^-2, respectively. Observed reduction in V_OC (D_it is from 1×10¹⁰ cm^-2 to 5×10¹³ cm^-2) may be due to the enhanced recombination possibility, which diminishes the difference in quasi Fermi energies from 0.8 eV to 0.46 eV. Reduction of J_SC (D_it is from 1×10¹³ cm^-2 to 5×10¹³ cm^-2) is connected with the carrier recombination rate that is heightened from 2.43×10²⁴cm^-3/s to 3.1×10²⁶cm^-3/s, which is markedly by two orders of magnitude. In addition, our research results demonstrate that by increasing the conduction band offset E_C (from 0.09eV to 0.15 eV), the V_OC could be increased by 15.9 mV, while the performance of HIT solar cells is not affected by the valence band offset E_V. The increase of E_C results in the rising of V_bi and thus improves V_OC. It is worth mention that, the recombination potential V_Re could be decreased from 232 meV to 208 meV by the increase of E_C (from 0.09eV to 0.15eV) and thus is favorable to V_OC. Consequently, when the interface state density is less than 10¹⁰ cm^-2 and the conduction band offset reaches 0.15eV, we can optimize the performance of HIT solar cells to achieve 24.95% efficiency.