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AND

JIN JANG"

Kyungpook Sanup University, College of General Education, Kyungsan, J•yungpook, 713-701, Korea Research Institute of Industrial Science & Technology, Automation Pvision, Pohang, Kyungpook, 790-330, Korea Kyung Hee University, Department of Physics, Seoul, 130-701, Korea ABSTRACTS

Hydrogenated amorphous silicon (a-Si:H) solar cells are prepared by plasma enhanced chemical vapor deposition (PECVD). Before quenching the solar cells, the short circuit current (J,,), open circuit voltage 2( Vo), fill factor (F. F.) and conversion efficiency (11) are 17.79 mA/cm , 0.79 V, 53.29, and 7.49 %, respectively. After thermal quenching2 the solar cells from 2000C, J, V,, , F. F., and 11 are 18.64 mA/cm , 0.8 V, 53.79, and 8.02 %, respectively. We investigated the thermal equilibrium processes of each P, I, and N layers. Also, we obtained the dark current-voltage characteristics of a-Si:H solar cells before and after quenching. We analyze the results in terms of the change of the internal electric field in a-Si:H solar cells, caused by the shift of the Fermi level of P layer toward valence band. INTRODUCTION

Ever since the initial studies of amorphous semiconductors, these materials have been divided into two categories. One group comprises the glasses, of which As 2Se3 and Se are well studied examples. Glasses have the property of being formed by cooling from the melt. During cooling the viscosity increases eventually to the point that structural changes are too slow to follow the cooling rate. The glass transition reflects the transition from a structure which is in metastable thermal equilibrium to one in which there is a frozen-in nonequilibrium state, from which slow relaxation can occur. The glass transition is kinetical][y determined, and occurs at a temperature that depends on the cooling rate of the glass. The second group is the "amorphous" materials, of which Si and Ge are the best known examples. These materials can not be made amorphous by cooling from the melt, and instead are typically deposited by evaporation, sputtering, or plasma decomposition. The general view of such deposition processes is that the resulting material will be far from thermal equilibrium. Instead, the structure will be solely determined by the way that the growing surface takes up the impinging atoms and forms a bonded network. Therefore,, in contrast to the glasses, the electronic properties are expected to vary strongly from sample to sample, depending on the details of the deposition. Evaporated a-Si contains about 1019 cm- 3 dangling-bond defects.[1] The defect density is reduced to about 1015 cM-3 in the best hydrogenated glow-discharge samples. [2]

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However, the glow-discharge technique can also produce high defect densities and columnar microstructure, depending on the details of the deposition.[31 On the other hand, the electronic properties of a-Si:H are not completely determined by the deposition process. For example, there are thermally ind