| Pacific Rim Symposium on Surfaces, Coatings and Interfaces (PacSurf 2016) | |
| Energy Harvesting & Storage | Wednesday Sessions |
| Session EH-WeP |
| Session: | Energy Harvesting & Storage Poster Session |
| Presenter: | Changhwan Choi, Hanyang University, Seoul, Korea, Republic of Korea |
| Authors: | M.S. Choi, Hanyang University, Seoul, Korea, Republic of Korea D.H. Lim, Hanyang University, Seoul, Korea, Republic of Korea Y.J. Kim, Hanyang University, Seoul, Korea, Republic of Korea H.H. Han, Hanyang University, Seoul, Korea, Republic of Korea S.K. Son, Hanyang University, Seoul, Korea, Republic of Korea J.H. Lee, Hanyang University, Seoul, Korea, Republic of Korea R.C. Choi, Inha University, Incheon, Korea, Republic of Korea CH. Choi, Hanyang University, Seoul, Korea, Republic of Korea |
| Correspondent: | Click to Email |
We synthesized and characterized Cu2ZnSnS4 (CZTS) thin film as an absorber layer using hybrid physical vapor deposition methods with a Sn/Cu/ZnS stack order on the Mo coated SLG (Soda lime glass) or SLG substrates. Considering melting temperature of each element, the first Sn layer was thermal-evaporated, followed by deposition of Cu and ZnS layers using Radio-Frequency (RF) magnetron sputtering. For the complete precursor, the final sulfurization process was carried out at 550 oC for 1 hour under the mixture gases of N2 + H2S (5%). ZnS was intentionally adopted to provide more sulfure into the film instead of using single Zn because some sulfur is lost during thermal processing. In order to investigate the effects of the elemental composition ratio within CZTS thin film on the structural, electrical and optical properties, the ratio of Sn: Cu: ZnS was modulated by adjusting the thickness of each element layers as following: (1) Sn (110 nm)/Cu (97 nm)/ZnS (243 nm), (2) Sn (132 nm)/Cu (109 nm)/ZnS (209 nm), (3) Sn (135 nm)/Cu (117 nm)/ZnS (198 nm), (4) Sn (134 nm)/Cu (138 nm)/ZnS (178 nm), and (5) Sn (134 nm)/Cu (158 nm)/ZnS (158 nm).
The CZTS thin film was turned out to be kesterite structure and the strongest preferred (112) orientation peak was detected to Cu/(Zn+Sn) ratio with 1.04. The Cu/(Zn+Sn) ratio substantially affects the peak intensity as well as growth and creation of secondary phases in the kesterite-structured CZTS films. In addition, the optical energy band gap (Eg) is significantly influenced by the composition ratio. Generally, increasing Cu/(Zn+Sn) ratio induced the growth of CZTS particle size leading to surface morphology improvement while the Eg was reduced. The moderate Cu/(Zn+Sn) ratio in the range between 0.53 and 1.04 led to enhance the kesterite structure of CZTS single crystal phase and reinforce growth direction of (112) preferred orientation. However, the Cu-rich films having Cu/(Zn+Sn) ratio greater than 1.0 showed much larger grain size due to agglomeration with adjacent grains. The Cu-rich CZTS thin film exhibited high carrier concentration (1.60×1020 cm-3) and hall mobility (9.8 cm2/V∙sec), but lower (1.18 eV) was attained. Instead, the Eg of Cu-poor CZTS thin film was 1.53 eV, favorable to the optimal CZTS absorber layer. Our results indicate that the optical energy band gap, an indicator to determining the optical properties of the CZTS thin film, is very sensitive to the composition ratio of constituent elements and PVD-based CZTS thin film should be carefully processed to get the optimum optical properties.