Effect of annealing on silicon heterojunction solar cells with textured ZnO:Al as transparent conductive oxide

Abstract

We report on silicon heterojunction solar cells using textured aluminum doped zinc oxide (ZnO:Al) as a transparent conductive oxide (TCO) instead of flat indium tin oxide. Double side silicon heterojunction solar cell were fabricated by radio frequency plasma enhanced chemical vapor deposition on high life time N-type float zone crystalline silicon wafers. On both sides of these cells we have deposited by radio frequency magnetron sputtering ZnO:Al layers of thickness ranging from 800 nm to 1400 nm. These TCO layers were then textured by dipping the samples in a 0.5% hydrochloric acid. External quantum efficiency as well as I-V under 1 sun illumination measurements showed an increase of the current for the cells using textured ZnO:Al. The cells were then annealed at 150• C, 175• C and 200• C during 30 min in ambient atmosphere and characterized at each annealing step. The results show that annealing has no impact on the open circuit voltage of the devices but that up to a 175• C it enhances their short circuit current, consistent with an overall enhancement of their spectral response. Our results suggest that ZnO:Al is a promising material to increase the short circuit current (Jsc) while avoiding texturing the c-Si substrate.

DC‐sputtered ZnO:Al as transparent conductive oxide for silicon heterojunction solar cells with µc‐Si:H emitter

“…For this optimized cell, we have deposited the ZnO:Al layer with 320 nm thickness at 300 °C, the oxygen flow of 0.5 sccm and the power density of 0.8 W/cm 2 determined from the individual studies. To the authors' knowledge, the obtained efficiency of 19.2% (on small area (5 × 5 mm 2 ) and without fabricating any metal grid) is among the highest efficiencies reported to this date for the SHJ solar cells with the DC‐sputtered ZnO:Al layers . This result demonstrates and confirms the potential of DC‐sputtered ZnO:Al layer as the promising TCO material for the future SHJ solar cells.…”

“…It should be noted that well‐known chemical texturing of the ZnO:Al is an advantage of this material that could provide additional light trapping in the SHJ devices . Figure (a) shows the EQE of the fabricated SHJ solar cell with 1.3 µm ZnO:Al layer thickness as deposited and after 25 s texturing with 1% HF aqueous solution.…”

“…In addition, it has been shown that In acts as a toxic element that could result into a toxic ITO compound . Moreover, ITO lacks texturing capability, and therefore, it needs to be combined with the wafer texturing . Therefore, replacing ITO with a cheaper, more abundant and environment‐friendly material with texturing capability seems to be a promising approach to reduce the cost of the future SHJ solar cells.…”