OPTIMIZATION OF PROPERTIES OF ZNO:B FILMS BY ANNEALING TREATMENT FOR CONVERSION EFFICIENCY IMPROVEMENT IN THIN FILM SILICON SOLAR CELLS

摘要

Zinc oxide thin films with same boron doping level and different thicknesses (ZnO:B) are prepared by low pressure chemical vapor deposition (LPCVD) technique and implemented in thin film silicon solar cells as front and back electrodes. The optical and electrical properties of ZnO:B films are systematically investigated through a post heat treatment in hydrogen and vacuum atmospheres at different annealing temperatures of 160, 180, 200 and 220 °C It is found that the optical properties, total transmission (TT) and haze value, of these films do not change at wavelength range from 300 to 1500nm after annealed treatment, nether in hydrogen or in vacuum atmosphere. However, the conductivity of ZnO:B films shows a remarkable increase after hydrogen annealing and a half decrease after the vacuum treatment, respectively. The conductivity changes variously with different thermal treating atmosphere, which are attributed to the variation of the carrier mobility of ZnO:B films by hydrogen and vacuum annealing treatment. Amorphous silicon thin film solar cells fabricated on the thinner ZnO:B films by a post hydrogen annealing treatment exhibit higher efficiency by 0.26% than ones on thicker ZnO:B films, which is mainly due to increased short-circuit current. The result in this paper provides a novel way to optimize electrical properties of thin ZnO:B films, which can lead to an increase in light-generated current and resulting a higher cell efficiency due to the enhancement of TT when thin-annealed ZnO:B films work as front contact in silicon thin film solar cells.