| 1. |
- Keller, Jan, et al.
(författare)
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On the Paramount Role of Absorber Stoichiometry in (Ag,Cu)(In,Ga)Se2 Wide‐Gap Solar Cells
- 2020
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Ingår i: Solar RRL. - : Wiley. - 2367-198X. ; 4:12
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Tidskriftsartikel (refereegranskat)abstract
- This contribution evaluates the effect of absorber off‐stoichiometry in wide‐gap (Ag,Cu)(In,Ga)Se2 (ACIGS) solar cells. It is found that ACIGS films show an increased tendency to form ordered vacancy compounds (OVCs) with increasing Ga and Ag contents. Very little tolerance to off‐stoichiometry is detected for absorber compositions giving the desired properties of 1) an optimum bandgap (EG) for a top cell in tandem devices (EG = 1.6–1.7 eV) and at the same time 2) a favorable band alignment with a CdS buffer layer. Herein, massive formation of either In‐ or Ga‐enriched OVC patches is found for group I‐poor ACIGS. As a consequence, carrier transport and charge collection are significantly impeded in corresponding solar cells. The transport barrier appears to be increasing with storage time, questioning the long‐term stability of wide‐gap ACIGS solar cells. Furthermore, the efficiency of samples with very high Ga and Ag contents depends on the voltage sweep direction. It is proposed that the hysteresis behavior is caused by a redistribution of mobile Na ions in the 1:1:2 absorber lattice upon voltage bias. Finally, a broader perspective on OVC formation in the ACIGS system is provided and fundamental limitations for wide‐gap ACIGS solar cells are discussed.
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| 2. |
- Keller, Jan, et al.
(författare)
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Performance Limitations of Wide-Gap (Ag,Cu)(In,Ga)Se2 Thin-Film Solar Cells
- 2021
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Ingår i: Solar RRL. - : John Wiley & Sons. - 2367-198X. ; 5:9
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Tidskriftsartikel (refereegranskat)abstract
- The effect of absorber stoichiometry in (Ag,Cu)(In,Ga)Se2(ACIGS) solar cells withbandgaps (Eg) > 1.40 eV is studied on a large sample set. It is conrmed thatmoving away in composition from ternary AgGaSe2by simultaneous reduction inGa and Ag content widens the chalcopyrite single-phase region and therebyreduces the amount of ordered vacancy compounds (OVCs). As a consequence, adistortion in currentvoltage characteristics, ascribed to OVCs at the back contact,can be successfully avoided. A clear anticorrelation between open-circuit voltage(VOC) and short-circuit current density (JSC) is detected with varying absorberstoichiometry, showing decreasingVOCand increasingJSCvalues for [I]/[III] > 0.9.Capacitance proling reveals that the absorber doping gradually decreases towardstoichiometric composition, eventually leading to complete depletion. It isobserved that only such fully depleted samples exhibit perfect carrier collection,evidencing a very low diffusion length in wide-gap ACIGS lms. The results indicatethat OVCs at the surface play a minor or passive role for device performance.Finally, a solar cell withVOC¼ 0.916 V atEg¼ 1.46 eV is measured, which is, to thebest of our knowledge, the highest value reported for this bandgap to date.
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| 3. |
- Bayrak Pehlivan, Ilknur, et al.
(författare)
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Electrochromic solar water splitting using a cathodic WO3 electrocatalyst
- 2021
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Ingår i: Nano Energy. - : Elsevier. - 2211-2855 .- 2211-3282. ; 81
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Tidskriftsartikel (refereegranskat)abstract
- Solar-driven water splitting is an emerging technology with high potential to generate fuel cleanly and sustainably. In this work, we show that WO3 can be used as a cathodic electrocatalyst in combination with (Ag,Cu) InGaSe2 solar cell modules to produce hydrogen and provide electrochromic functionality to water splitting devices. This electrochromic effect can be used to monitor the charge state or performance of the catalyst for process control or for controlling the temperature and absorbed heat due to tunable optical modulation of the electrocatalyst. WO3 films coated on Ni foam, using a wide range of different sputtering conditions, were investigated as cathodic electrocatalysts for the water splitting reaction. The solar-to-hydrogen (STH) efficiency of solar-driven water electrolysis was extracted using (Ag,Cu)InGaSe2 solar cell modules with a cell band gap varied in between 1.15 and 1.25 eV with WO3 on Ni foam-based electrolyzers and yielded up to 13% STH efficiency. Electrochromic properties during water electrolysis were characterized for the WO3 films on transparent substrate (indium tin oxide). Transmittance varied between 10% and 78% and the coloration efficiency at a wavelength of 528 nm and the overpotential of 400 mV was 40 cm(2) C-1. Hydrogen ion consumption in ion intercalation for electrochromic and hydrogen gas production for water electrolysis processes was discussed.
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| 4. |
- Bayrak Pehlivan, Ilknur, et al.
(författare)
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NiMoV and NiO-based catalysts for efficient solar-driven water splitting using thermally integrated photovoltaics in a scalable approach
- 2021
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Ingår i: iScience. - : Cell Press. - 2589-0042. ; 24:1
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Tidskriftsartikel (refereegranskat)abstract
- In this work, a trimetallic NiMoV catalyst is developed for the hydrogen evolution reaction and characterized with respect to structure, valence, and elemental distribution. The overpotential to drive a 10 mA cm−2 current density is lowered from 94 to 78 mV versus reversible hydrogen electrode by introducing V into NiMo. A scalable stand-alone system for solar-driven water splitting was examined for a laboratory-scale device with 1.6 cm2 photovoltaic (PV) module area to an up-scaled device with 100 cm2 area. The NiMoV cathodic catalyst is combined with a NiO anode in alkaline electrolyzer unit thermally connected to synthesized (Ag,Cu) (In,Ga)Se2 ((A)CIGS) PV modules. Performance of 3- and 4-cell interconnected PV modules, electrolyzer, and hydrogen production of the PV electrolyzer are examined between 25°C and 50°C. The PV-electrolysis device having a 4-cell (A)CIGS under 100 mW cm−2 illumination and NiMoV-NiO electrolyzer shows 9.1% maximum and 8.5% averaged efficiency for 100 h operation.
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| 5. |
- Calnan, Sonya, et al.
(författare)
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Development of Various Photovoltaic‐Driven Water Electrolysis Technologies for Green Solar Hydrogen Generation
- 2021
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Ingår i: Solar RRL. - : John Wiley & Sons. - 2367-198X. ; 6:5
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Tidskriftsartikel (refereegranskat)abstract
- Direct solar hydrogen generation via a combination of photovoltaics (PV) and water electrolysis can potentially ensure a sustainable energy supply while minimizing greenhouse emissions. The PECSYS project aims at demonstrating asolar-driven electrochemical hydrogen generation system with an area >10 m2 with high efficiency and at reasonable cost. Thermally integrated PV electrolyzers(ECs) using thin-film silicon, undoped, and silver-doped Cu(In,Ga)Se2 and silicon heterojunction PV combined with alkaline electrolysis to form one unit are developed on a prototype level with solar collection areas in the range from 64 to2600 cm2 with the solar-to-hydrogen (StH) efficiency ranging from 4 to 13%. Electrical direct coupling of PV modules to a proton exchange membrane EC test the effects of bifacially (730 cm2 solar collection area) and to study the long-term operation under outdoor conditions (10 m2 collection area) is also investigated. In both cases, StH efficiencies exceeding 10% can be maintained over the test periods used. All the StH efficiencies reported are based on measured gas outflow using mass flow meters.
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| 6. |
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| 7. |
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| 8. |
- Keller, Jan, et al.
(författare)
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Rubidium Fluoride Absorber Treatment for Wide-Gap (Ag,Cu)(In,Ga)Se-2 Solar Cells
- 2022
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Ingår i: Solar RRL. - : John Wiley & Sons. - 2367-198X. ; 6:6
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Tidskriftsartikel (refereegranskat)abstract
- This contribution studies the potential of an RbF postdeposition treatment (RbF-PDT) of wide-gap (Ag,Cu)(In,Ga)Se-2 (ACIGS) absorbers to improve the corresponding solar cell performance. While a higher open-circuit voltage (V-OC) and short-circuit current density are achieved, a lower fill factor (FF) is observed for most of the devices subjected to an RbF-PDT. However, the drop in FF can be avoided for some close-stoichiometric samples, leading to maximum efficiencies beyond 16% (without antireflection coating) at a bandgap energy (E-g) of 1.43 eV. For off-stoichiometric ACIGS, a record V-OC value of 926 mV at E-g = 1.44 eV is reached. Lower V-OC deficits likely require enhanced bulk quality of wide-gap chalcopyrite absorbers. Extensive material analysis shows that the heavy alkali PDT of ACIGS with high Ag and Ga contents leads to similar absorber modifications as commonly observed for low-gap Cu(In,Ga)Se-2 (CIGS). Rubidium is continuously distributed at "internal" (grain boundaries) and "external" (buffer and back contact) absorber interfaces. The results indicate that Rb diffusion into the absorber bulk (including 1:1:2 and 1:3:5 compounds) is restricted. Furthermore, the formation of a very thin RbInSe2 surface layer is suggested. It remains open, which effects alter the device characteristics after RbF-PDT.
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| 9. |
- Keller, Jan, et al.
(författare)
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Silver Alloying in Highly Efficient CuGaSe2 Solar Cells with Different Buffer Layers
- 2023
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Ingår i: Solar RRL. - : John Wiley & Sons. - 2367-198X. ; 7:12
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Tidskriftsartikel (refereegranskat)abstract
- This study evaluates the effect of silver alloying, stoichiometry, and deposition temperature of wide-gap (Ag,Cu)GaSe2 (ACGS) absorber films for solar cell applications. Devices using a standard CdS buffer exhibit a strong anticorrelation between the open-circuit voltage (V-OC) and short-circuit current density (J(SC)), with V-OC decreasing and J(SC) increasing toward stoichiometric absorber composition. Increasing the ACGS deposition temperature leads to larger grains and improved J(SC), while V-OC is not affected. By adding more silver to the absorber (maximum tested [Ag]/([Ag]+[Cu]) [AAC] = 0.4), the widening of the space charge region (SCR) significantly enhances carrier collection. Experimental quantum efficiency spectra can be accurately simulated when assuming a very low diffusion length and perfect collection in the SCR. The highest efficiency of 8.3% (without antireflection coating [ARC]) is reached for an absorber with AAC = 0.4 grown at 600 degrees C. Replacing CdS by a (Zn,Sn)O buffer with lower electron affinity strongly mitigates interface recombination. Moreover, the V-OC-J(SC) anticorrelation is not evident anymore and the highest efficiency of 11.2% (11.6% w/ARC, V-OC = 985 mV, J(SC) = 18.6 mA cm(-2), fill factor = 61.0%) is reached for a close-stoichiometric ACGS solar cell with AAC = 0.4 processed at 650 degrees C.
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| 10. |
- Keller, Jan, et al.
(författare)
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Wide-Gap Chalcopyrite Solar Cells with Indium Oxide-Based Transparent Back Contacts
- 2022
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Ingår i: Solar RRL. - : John Wiley & Sons. - 2367-198X. ; 6:8
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Tidskriftsartikel (refereegranskat)abstract
- Herein, the performance of wide-gap Cu(In,Ga)Se-2 (CIGS) and (Ag,Cu)(In,Ga)Se-2 (ACIGS) solar cells with In2O3:Sn (ITO) and In2O3:H (IOH) as transparent back contact (TBC) materials is evaluated. Since both TBCs restrict sodium in-diffusion from the glass substrate, fine-tuning of a NaF precursor layer is crucial. It is found that the optimum Na supply is lower for ACIGS than for CIGS samples. An excessive sodium amount deteriorates the solar cell performance, presumably by facilitating GaOx growth at the TBC/absorber interface. The efficiency (eta) further depends on the absorber stoichiometry, with highest fill factors (and eta) reached for close-stoichiometric compositions. An ACIGS solar cell with eta = 12% at a bandgap of 1.44 eV is processed, using IOH as a TBC. The best CIGS device reaches eta = 11.2% on ITO. Due to its very high infrared transparency, IOH is judged superior to ITO for implementation in a top cell of a tandem device. However, while ITO layers maintain their conductivity, IOH films show an increased sheet resistance after absorber deposition. Chemical investigations indicate that incorporation of Se during the initial stage of absorber processing may be responsible for the deteriorated conductivity of the IOH back contact in the final device.
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