Hole-Selective Front Contact Stack Enabling 24.1%-Efficient Silicon Heterojunction Solar Cells

Abstract

The window-layer stack limits the efficiency of both-side-contacted silicon heterojunction solar cells. We discuss here the combination of several modifications to this stack to improve its optoelectronic performance. These include the introduction of a nanocrystalline silicon-oxide p-type layer in lieu of the amorphous silicon p-type layer, replacing indium tin oxide with a zirconium-doped indium oxide for the front transparent electrode, capping this layer with a silicon-oxide film, and applying a post-fabrication electrical biasing treatment. The influence of each of these alterations is discussed, as well as their interactions. Combining all of them finally enables the fabrication of a highly transparent and electrically well-performing windowlayer stack, leading to a screen-printed silicon heterojunction solar cell with 24.1% efficiency. Paths towards industrialization and for further improvements are finally discussed.

Influence of Light Soaking on Silicon Heterojunction Solar Cells With Various Architectures

“…The mechanism behind the reduction of RS is not yet identified. ncSiOx:H(p) layers outperform devices using a-Si:H(p) layers while simultaneously improving under light soaking [35]. Our results suggest that to maximise the final efficiency and benefit from the light soaking treatment, the (p) layer should be slightly thicker than optimum, and the (i) layer as thin as possible.…”

“…Thus, we observe that for thick microcrystalline (p) layers the final efficiency might be lower than cells with an optimised a-Si:H(p) layer, caused by large parasitic light absorption, despite the more important light soaking gain, as shown by the green dots in Figure 5. Note that this is a matter of optimization, since devices using recently optimized ncSiOx:H(p) layers outperform devices using a-Si:H(p) layers while simultaneously improving under light soaking [35]. Our results suggest that to maximise the final efficiency and benefit from the light soaking treatment, the (p) layer should be slightly thicker than optimum, and the (i) layer as thin as possible.…”

Very Thin (56 μm) Silicon Heterojunction Solar Cells with an Efficiency of 23.3% and an Open‐Circuit Voltage of 754 mV

“…For some SHJ cells, an additional SiO X antireflection coating with a thickness of ≈100 nm was deposited by means of PECVD using SiH 4 and CO 2 as source gases. [ 52,53 ]…”

“…For some SHJ cells, an additional SiO X antireflection coating with a thickness of %100 nm was deposited by means of PECVD using SiH 4 and CO 2 as source gases. [52,53] Characterization of SHJ Cells: The current density-voltage ( J-V ) characteristics of the SHJ cell were evaluated using a solar simulator under STCs (100 mWcm À2 , air mass 1.5 global, 25 C) using a class AAA solar simulator (Wacom), and the V OC , the J SC , the FF, and the conversion efficiency (η) were recorded. The cell area was 4 cm 2 designated by a black shadow mask during the measurement.…”

“…We also applied an additional SiO X -based AR coating to some very thin SHJ cells with high efficiencies for reducing the primary reflection loss further, [52,53] and the best-efficiency cell was then independently characterized by AIST Photovoltaic Calibration, Standards and Measurement Team under STCs (100 mWcm À2 , air mass 1.5 global, 25 C). As a result, we obtained V OC ¼ 754 mV, J SC ¼ 37.85 mA cm À2 , FF ¼ 81.5%, and η ¼ 23.27% for a very thin (w ¼ 56.2 μm) SHJ solar cell with the (p)nc-Si:H window layer, as shown in Figure 2h.…”