Low Surface Recombination Velocity on P-Type Cz-Si Surface by Sol-Gel Deposition of Al2O3 Films for Solar Cell Applications

Abstract

High quality surface passivation has gained a significant importance in photovoltaic industry for fabricating low cost and high efficiency solar cells using thinner and lower cost wafers. The passivation property of spin coated Al2O3 films with a thickness of about 50 nm on p-type Cz Si wafers has been investigated as a function of annealing temperatures. An effective surface recombination velocity of 55 cm/s was obtained for the films annealed at 500 degrees C. The chemical and field effect passivation was analyzed by C V measurements. A high density of negative fixed charges (Q(f)) in the order of 9 x 10(-1) cm(-2) was detected in Al2O3 films and its impact on the level of surface passivation was demonstrated experimentally. The C V curves show density of the interface state (DR) of 1 x 10(12) eV(-1)cm(-2) at annealing temperature of 500 degrees C. During annealing, a thin interfacial SiOx is formed, and this interfacial layer is supposed to play a vital role in the origin of negative Q(f) and D-it. The homogeneous SiOx interlayer result in higher passivation performance due to both the increase of negative Q(f) and the decrease of D-it.