An analytical model to explore open-circuit voltage of a-Si:H/c-Si heterojunction solar cells

Abstract

The effect of the parameters on the open-circuit voltage, V_OC of a-Si:H/c-Si heterojunction solar cells was explored by an analytical model. The analytical results show that V_OC increases linearly with the logarithm of illumination intensity under usual illumination. There are two critical values of the interface state density (D_it) for the open-circuit voltage (V_OC), D_it^crit,1 and D_it^crit,2 (a few 10¹⁰ cm⁻²∙eV⁻¹). V_OC decreases remarkably when D_it is higher than D_it^crit,1. To achieve high V_OC, the interface states should reduce down to a few 10¹⁰ cm⁻²·eV⁻¹. Due to the difference between the effective density of states in the conduction and valence band edges of c-Si, the open-circuit voltage of a-Si:H/c-Si heterojunction cells fabricated on n-type c-Si wafers is about 22 mV higher than that fabricated on p-type c-Si wafers at the same case. V_OC decreases with decreasing the a-Si:H doping concentration at low doping level since the electric field over the c-Si depletion region is reduced at low doping level. Therefore, the a-Si:H layer should be doped higher than a critical value of 5×10¹⁸ cm⁻³ to achieve high V_OC.

Keywords

solar cells / a-Si:H/c-Si heterojunctions / open-circuit voltage

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