ITO/p+nc-Si:H contact barrier effects on n-i-p′-p silicon solar cell performances

The computer program AMPS-1D (analysis of microelectronic and photonic structures) has been used to explore the effect of front contact barrier heights for electrons (φb0) or holes (φh) on the performances of n-i-p′-p amorphous/nanocrystalline silicon based solar cell, with a p type hydrogenated nanocrystalline silicon double layer and with no back reflector. φb0 is the result of band bending at the indium tin oxide (ITO)/p+doped hydrogenated nanocrystalline silicon (p nc-Si:H) interface. This paper presents results for a n-i-p′-p device, when the p nc-Si:H layer is used as a window and the p′-nc-Si:H layer as a buffer. Band diagram at thermodynamic equilibrium and current–voltage characteristics (J–V), under dark and illumination conditions, for the considered solar cell structure, are calculated. The modeling showed that the reverse bias currents do not depend on the front contact barrier heights. However, in the forward direction, this contact barrier influences strongly the J–V characteristic in the dark and under illumination. As a result, when φb0 increases, output cell parameters, like open circuit voltage (VOC), fill factor (FF) and efficiency (Eff) increase. The best values obtained are 0.893 V, 0.757 and 8.04%, respectively. These values correspond to a front contact barrier height (φb0) equal to 1.65 eV. Such a value of φb0 can be realized experimentally by using an indium tin oxide (ITO) front contact electrode, with a work function value about 5.35 eV.