Sputtered Copper Zinc Tin Sulfur Films And Preliminary Study Of CZTS/In₂S₃ Heterojunction

Copper zinc tin sulfur (Cu2ZnSnS4, CZTS) thin film is a quaternary I2-II-IV-VI4 compound semiconductor. It has some advantages, such as abundant raw materials, cheap cost in the earth, high absorption coefficient (>1 × 104cm-1), and appropriate band gap (1.50 eV). The theoretical photoelectric conversion efficiency of CZTS solar cell is 32.2%. Based on above advantages, the CZTS thin films have become one of the best candidates as solar cell absorption layers instead of copper indium gallium tin (CuInGaSe2). During the process of preparing the CZTS thin films, there normally exist some problems such as non-uniformity and secondary phases. In order to solve the above problems, we tried to prepare the CZTS films by sputtering alloy target. In this thesis, CZTS thin films were synthesized on glass substrates by sulfurizing the sputtered metal precursors. The influences of the preparation parameters on the structure, surface morphology, optical and electrical properties of the thin films were also investigated. And the CZTS/In2S3 heterojunctions were prepared and studied. The main results are demonstrated as follows.1. The influences of sputtering power and pressure on the photoelectric properties of CZTS thin films were studied. The CZTS thin films were obtained by sulfurizing CZT thin films deposited by RF magnetron sputtering at temperatures of 500 ℃ for 2 h in an atmosphere of hydrogen sulfide and nitrogen. Our experimental results show that, with the increasing of the sputtering power, the mobility is increased gradually, and the resistivity is decreased first and then increased. With the increasing of the sputtering pressure, the carrier concentration is decreased first and then increased, but the mobility and resistivity are increased first and then decreased. The CZTS thin films exhibit the better properties than others when the sputtering power and sputtering pressure of the CZT precursors was 90 W and 2.0 Pa, respectively.2. The influence of hydrogen sulfide concentration on the properties of CZTS thin films was investigated. The experimental results show that, with the increasing of the hydrogen sulfide concentration, the carrier concentration is decreased first and then increased, but the mobility and resistivity is increased first and then decreased. The CZTS thin films exhibit the optimum properties when the hydrogen sulfide concentration is 5%. The optical band gap, the carrier concentration, the resistivity and the mobility of CZTS thin film is 1.50 eV,2.07 × 1018 cm-3,2.37 Ω·cm and 1.38 cm2·s-1·v-1, respectively. The results show the CZTS flims are suitable for the absorption layers of the solar cells.3. The ohmic contact characteristic of four kinds of metals (silver, copper, aluminum and indium) with the In2S3 thin film was explored. The results show that four kinds of metals have a good ohmic contact with the In2S3 thin film. The series resistance between metal Ag and the In2S3 thin film is the minimum. The contact characteristic of the Al electrode with the CZTS thin film was studied. The Ⅰ-Ⅴ characteristic curve shows that the Al electrode with CZTS thin film has formed a good ohmic contact.4. The energy band structure of CZTS/In2S3 heterojunction and the photoelectric properties of the CZTS/In2S3 heteroj unction were studied. The conduction band offset ΔEc of CZTS/In2S3 heterojunction is 0.82 eV. It is greater than the allowed value of the AEc (0 eV< AEc< 0.4 eV), which will stop the electrons moving from the absorption layer into the buffer layer. The Ⅰ-Ⅴ characteristic curve shows that the CZTS/In2S3 heterojunction has a good rectifying characteristic.