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

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 10(10) cm(-2)a (TM) 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 10(10) cm(-2)center dot 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 5x10(18) cm(-3) to achieve high V (OC).