A statistical approach for the optimization of indium tin oxide films used as a front contact in amorphous/crystalline silicon heterojunction solar cells

In heterojunction silicon with intrinsic thin layer (HIT) solar cells, the excellent opto-electrical properties of indium tin oxide (ITO) front contact play a critical role in attaining high efficiency. Therefore, in this study, we present and demonstrate an effective statistic approach based on combining Taguchi method and Grey relational analysis for the optimization of ITO films. A reduction in the number of experiments by approximately 90% is obtained by the Taguchi method through an orthogonal array. The reproduction of the effect of process parameters on single performance characteristic, however, is still ensured. In addition, an excellent trade-off between electrical and optical properties of ITO films was attained within the selected range of parameters by Grey relational analysis at power density of 0.685 W/cm(2), working pressure of 0.4 Pa, substrate temperature of 200 degrees C, and post-annealing temperature of 200 degrees C in 30 min. Under optimal condition, the ITO films showed lowest electrical resistivity of 1.978 x 10(-4) Omega cm, and highest transmittance of 90.322%. The HIT solar cells using these ITO films as a front contact show highest efficiency of 16.616%, yielding a 1.750% absolute increase in efficiency compared to using ITO films with the initial condition. Furthermore, the analysis of variance (ANOVA) is determined to define the process parameters which have a dominant effect on the electrical and optical properties of ITO films. Based on ANOVA, we found that the substrate temperature was a key parameter which critically affects the optoelectrical properties of ITO films. (C) 2014 Elsevier Ltd. All rights reserved.