EFFECT OF ANNEALING ON STRUCTURAL AND OPTICAL PROPERTIES OF Na-INCORPORATED CuInS2 THIN FILMS

摘要

CuInS2 and related chalcopyrites are one of the most promising materials for absorber in polycrystalline thin film solar cells due to their direct band gap, high absorption coefficient and good stability. Recently, the sodium effect has become one of the important factors affecting the energy conversion efficiency of solar cells using CuInS2 thin films as absorption layers. Enhancements in conductivity, crystallite quality and device performance in controlled-Na incorporated CuInS2 have been reported. We have investigated in this work, the optical properties of Na-incorporated CuInS2 thin films grown by the single source thermal evaporation method. The amount of the Na source was determined to be 0-1 at.% compared with CuInS2 source The films were annealed from 350 to 500°C in vacuum after evaporation. The absorption coefficients above the fundamental band edge for all thin films exceed 3.104 cm-1 and in particular for the layer with amount 0.5at%, the absorption coefficient exceeds 105 cm-1 independently of the annealing temperature. Then, the films are suitable for thin-film photovoltaic. In addition, we note an improvement in the fundamental absorption edge with the increasing of the annealing temperature. The optical band gap is increased for each amount with increasing the annealing temperature. The films showed p type conductivity after annealing and an improvement in the film conductivities is observed with increasing annealing temperature.