| 1. |
|
|
| 2. |
- Anacleto, Pedro, et al.
(författare)
-
Precisely nanostructured HfO2 rear passivation layers for ultra-thin Cu(In,Ga)Se-2
- 2022
-
Ingår i: Progress in Photovoltaics. - : John Wiley & Sons. - 1062-7995 .- 1099-159X. ; 30:11, s. 1289-1297
-
Tidskriftsartikel (refereegranskat)abstract
- The quest for material-efficient Cu(In,Ga)Se-2 (CIGS) solar cells encourages the development of ultra-thin absorbers. Their use reduces material consumption and energy usage during production by increasing the throughput. Thereby, both the bill of materials as well as the energy and capital costs are reduced. However, because thin absorbers are prone to increase back contact recombination, back surface passivation schemes are necessary to reach a similar or higher conversion efficiency than for absorbers with conventional thickness. Here, we investigate nanostructured hafnium oxide (HfO2) rear passivation layers for ultra-thin CIGS solar cells. We fabricate regular arrays of point contacts with 200 nm diameter through HfO2 layers with thicknesses between 7 and 40 nm using electron beam lithography and reactive ion etching. The current-voltage curves of solar cells with a 500 nm thick CIGS absorber layer and the nanostructured passivation layer show improved performance concerning V-oc and J(sc) compared to non-passivated reference devices. Furthermore, external quantum efficiency and optical reflection confirm an effective passivation behavior, with an average efficiency increase of up to 1.2% for the cells with the 40 nm thick HfO2 layer. In addition, simulation work shows that even 40 nm thick HfO2 passivation layers have only a minimal effect on the optical properties of ultra-thin CIGS solar cells, and hence, the photocurrent increase verified experimentally stems from electrical improvements caused by the HfO2 layer passivation effect. We also investigate the impact of ultra-thin (0.3, 0.6, 1.3, and 2.5 nm) non-patterned HfO2 passivation layers on the same type of solar cells. However, these results showed no improvement in solar cell performance, despite an increase in the current density with layer thickness.
|
|
| 3. |
- Apell, Peter, 1952, et al.
(författare)
-
High optical absorption in graphene
- 2012
-
Ingår i: arXiv.
-
Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
- A simple analysis is performed for the absorption properties of graphene sandwiched between two media. For a proper choice of media and graphene doping/gating one can approach 50-100% absorption in the GHz-THz range for the one atom thick material. This absorption is controlled by a characteristic chemical potential which depends only on carrier life-time and the indexes of refraction of the dielectric embedding.
|
|
| 4. |
|
|
| 5. |
|
|
| 6. |
|
|
| 7. |
|
|
| 8. |
- Bilousov, Oleksandr V., et al.
(författare)
-
ALD of phase controlled tin monosulfide thin films
- 2017
-
Konferensbidrag (refereegranskat)abstract
- Tin monosulfide (SnS) is a promising semiconductor material for low-cost conversion of solar energy, playing the role of absorber layer in photovoltaic devices. SnS is, due to its high optical damping, also an excellent semiconductor candidate for the realization of ultrathin (nanoscale thickness) plasmonic solar cells [1].Here, we present an important step to further control and understand SnS film properties produced using low temperature ALD with Sn(acac)2 and H2S as precursors. We show that the SnS film properties vary over a rather wide range depending on substrate temperature and reaction conditions, and that this is connected to the growth of cubic (π-SnS) and orthorhombic SnS phases. The optical properties of the two polymorphs differ significantly, as demonstrated by spectroscopic ellipsometry [2].1. C. Hägglund, G. Zeltzer, R. Ruiz, A. Wangperawong, K. E. Roelofs, S. F. Bent, ACS Photonics 3 (3) (2016) 456–463.2. O. V. Bilousov, Y. Ren, T. Törndahl, O. Donzel-Gargand , T. Ericson, C. Platzer-Björkman, M. Edoff, and C. Hägglund, ACS Chemistry of Materials 29 (7) (2017) 2969–2978.
|
|
| 9. |
- Bilousov, Oleksandr V., et al.
(författare)
-
Atomic Layer Deposition of Cubic and Orthorhombic Phase Tin Monosulfide
- 2017
-
Ingår i: Chemistry of Materials. - : AMER CHEMICAL SOC. - 0897-4756 .- 1520-5002. ; 29:7, s. 2969-2978
-
Tidskriftsartikel (refereegranskat)abstract
- Tin monosulfide (SnS) is a promising light-absorbing material with weak environmental constraints for application in thin film solar cells. In this paper, we present low-temperature atomic layer deposition (ALD) of high-purity SnS of both cubic and orthorhombic phases. Using tin(II) 2,4-pentanedionate [Sn(acac)(2)] and hydrogen sulfide (H2S) as precursors, controlled growth of the two polymorphs is achieved. Quartz crystal microbalance measurements are used to establish saturated conditions and show that the SnS ALD is self-limiting over temperatures from at least 80 to 160 degrees C. In this temperature window, a stable mass gain of 19 ng cm(-2) cycle(-1) is observed. The SnS thin film crystal structure and morphology undergo significant changes depending on the conditions. High-resolution transmission electron microscopy and X-ray diffraction demonstrate that fully saturated growth requires a large H2S dose and results in the cubic phase. Smaller H2S doses and higher temperatures favor the orthorhombic phase. The optical properties of the two polymorphs differ significantly, as demonstrated by spectroscopic ellipsometry. The orthorhombic phase displays a wide (0.3-0.4 eV) Urbach tail in the near-infrared region, ascribed to its nanoscale structural disorder and/or to sulfur vacancy-induced gap states. In contrast, the cubic phase is smooth and void-free and shows a well-defined, direct forbidden-type bandgap of 1.64 eV.
|
|
| 10. |
- Bilousov, Oleksandr V., et al.
(författare)
-
Substrate Effects on Crystal Phase in Atomic Layer Deposition of Tin Monosulfide
- 2021
-
Ingår i: Chemistry of Materials. - : American Chemical Society (ACS). - 0897-4756 .- 1520-5002. ; 33:8, s. 2901-2912
-
Tidskriftsartikel (refereegranskat)abstract
- Obtaining single-phase tin monosulfide (SnS) films at low temperatures is challenging since cubic (π-SnS) and orthorhombic (α-SnS) polymorphs have similar energies of formation and grow under similar conditions. Here, we show that in atomic layer deposition (ALD) of polycrystalline SnS using tin(II) acetylacetonate and H2S precursors, the substrate surface greatly influences the SnS phase evolution. For example, a silicon (100) substrate, with a highly hydroxylated surface, favors the growth of α-SnS. Meanwhile, ozone treatment or preannealing of the same substrate leads to mainly π-SnS. Just a few ALD cycles of another oxide or sulfide can even more substantially alter the outcome. Substrates that favor α-SnS growth typically produce initially enhanced growth rates, while those promoting π-SnS are partially surface-poisoned by the acetylacetonate precursor ligands. Growth of either polymorph is self-sustained after its initiation, and the sustaining factor appears to be the surface–ligand interaction; π-SnS preferentially evolves on substrates and π-SnS surfaces that are rich in highly reactive dangling bonds, while chemically inert substrates and α-SnS surfaces promote α-SnS. While lattice matching is less central, the role of ligand bonding in SnS ALD also helps explain the previously reported phase dependence on growth temperature and H2S precursor dose and shows promise for area-selective ALD of SnS.
|
|
