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

Abstract

Silicon heterojunction (SHJ) solar cells are highly interesting, because of their high efficiency and low cost fabrication. So far, the most applied transparent conductive oxide (TCO) is indium tin oxide (ITO). The replacement of ITO with cheaper, more abundant and environmental friendly material with texturing capability is a promising way to reduce the production cost of the future SHJ solar cells. Here, we report on the fabrication of the SHJ solar cells with direct current-sputtered aluminum-doped zinc oxide (ZnO:Al) as an alternative TCO. Furthermore, we address several important differences between ITO and the ZnO:Al layers including a high Schottky barrier at the emitter/ZnO:Al interface and a high intrinsic resistivity of the ZnO:Al layers. To overcome the high Schottky barrier, we suggest employing micro-crystalline silicon (μc-Si:H) emitter, which also improves temperature threshold and passivation of the solar cell precursor. In addition, we report on the extensive studies of the effect of the ZnO:Al deposition parameters including layer thickness, oxygen flow, power density and temperature on the electrical properties of the fabricated SHJ solar cells. Finally, the results of our study indicate that the ZnO:Al deposition parameters significantly affect the electrical properties of the obtained solar cell. By understanding and fine-tuning all these parameters, a high conversion efficiency of 19.2% on flat wafer (small area (5 × 5 mm 2 ) and without any front metal grid) is achieved.

Prolonged Annealing Improves Hole Transport of Silicon Heterojunction Solar Cells

“…[ 19 ] Another option is to adjust the work function of the p‐a‐Si:H layer by increasing the net doping or applying its microcrystalline structure. [ 20 ] Bivour et al showed that high doping of the p‐a‐Si:H layer was required for the formation of an efficient tunneling junction at the p‐a‐Si:H/ITO contact. [ 21 ]…”

Heterojunction solar cells with 23% efficiency onn-type epitaxial kerfless silicon wafers

“…Hydrogenated amorphous silicon (a‐Si:H)/crystalline silicon (c‐Si) heterojunction (HJ) solar cells are the focus of a considerable amount of research because they can achieve high conversion efficiencies with simple fabrication processes . For this type of cell, the highest reported short‐circuit current density ( J sc ), open‐circuit voltage ( V oc ), and fill factor (FF) are 39.5 mA cm −2 , 750 mV, and 0.832, respectively, for a 98‐µm‐thick Czochralski (Cz) c‐Si wafer with a non‐back‐contact structure .…”

Influence of atmosphere and material properties on damp heat stability of ZnO:Al

“…Aluminum doped zinc oxide (ZnO:Al) is used as front or part of the back contact of thin‐film PV technology . Recently, ZnO:Al has been applied successfully to silicon heterojunction solar cells as well . Solar modules and in particular the contact materials must withstand long term outdoor operation.…”