Optimizing transparent conductive Al-doped ZnO thin films for SiN_x free crystalline Si solar cells

Al-doped ZnO (AZO) thin films with resistivity of 6.6 × 10⁻⁴ Ω cm were prepared by introducing H₂ in DC magnetron sputtering atmosphere. The Hall Effect measurement demonstrates that a part of the hydrogen atoms act as shallow donors while others act as neutral scattering impurities. Only proper H₂ partial pressure decreases the resistivity to the lowest value. The properties of SiN_x free crystalline Si (c-Si) solar cells were improved when AZO thin films were applied. The films served as both anti-reflection (AR) coatings and front electrode assistance. Ensuring an outstanding AR effect and a low sheet resistance, the thickness of the films was optimized in order to reduce the optical absorption, and thus effectively increase the short circuit current density (J_sc). The influence of the films versus different Ag fingers and emitter sheet resistance was investigated. The results showed that the J_sc was improved apparently (at least by 0.7 mA/cm²), while the fill factor was enhanced obviously from 62 to 70 % and from 73 to 75 %, respectively, which depended on the initial series resistance.