DETERMINATION OF ELECTRON-DIFFUSION LENGTH FROM PHOTOCURRENT CHARACTERISTICS OF THE STRUCTURE ITO A-SICH (P-TYPE) A-SIH A-SIH (N-TYPE) PD

In this study the electron diffusion length L(n) is determined from th e relative spectral response of the photocurrent characteristics of th e p/i/n sandwich structure ITO/a-SiC:H (p-type)/a-Si:H/a-Si:H (n-type) /Pd. The techniques used for the preparation of the a-Sic:H and a-Si:H amorphous films were glow-discharge and rf magnetron sputtering, resp ectively. The thickness of the p-type, intrinsic and n-type layer were 400 angstrom, 7000 angstrom and 600 angstrom, respectively. The respo nse of the short-circuit current density J(sc) was measured versus the photon energy hv at both constant light intensity and constant temper ature. The electron diffusion length was found to be 0.31 mum by means of the method of Agarwala and Tewary. Although, in the case of single crystals many diffusion length measurements have been made, there are only few papers for amorphous silicon this films [1]. As it is well-k nown, the diffusion length of the charge carriers is the most importan t parameter from the point of view of solar cell applications [2]. In order to obtain a high efficiency in a solar cell all carriers created under illumination in the intrinsic layer should reach the electrodes [3]. In the case that the thickness of the intrinsic layer is much la rger than the diffusion length, not all carriers can reach the electro des and, accordingly, a low efficiency results [4]. On the other hand, carriers which reach the electrodes without thermalizing do not contr ibute to the photocurrent and finally the efficiency of the solar cell is negatively affected. In order to avoid such an effect to a large e xtent, the thickness of the amorphous layers in a p/i/n solar cell mus t be conveniently chosen compared to the diffusion length of the carri ers. Here it is aimed to determine the electron diffusion length. In o rder to achieve this goal, the photocurrent characteristics of an ITO/ a-SiC:H(p-type)/a-Si:H/a-Si:H(n-type)/Pd structure was measured versus the photon energy at constant light intensity and constant temperatur e. In order to determine the electron diffusion length, the method of Agarwala and Tewary [5] was utilized.