Efficiency increased to 15.2% for ultra‐thin Cu(In,Ga)Se<sub>2</sub> solar cells

Mansfield, Lorelle M.; Kanevce, Ana; Harvey, Steven P.; Bowers, Karen; Beall, Carolyn; Glynn, Stephen; Repins, Ingrid

doi:10.1002/pip.3033

Cited by 51 publications

(56 citation statements)

References 25 publications

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“…In addition, they have focused on ultra‐thin (≤500 nm) CIGSe solar cells with sufficiently high efficiencies, [ 9–11 ] which have been recently reported to reach 15.2% with Mo BCs. [ 12 ] However, STUT CIGSe solar cells are still less efficient due to several limitations. Furthermore, F‐STUT CIGSe solar cells have not been studied extensively.…”

Section: Introductionmentioning

confidence: 99%

Flexible and Semi‐Transparent Ultra‐Thin CIGSe Solar Cells Prepared on Ultra‐Thin Glass Substrate: A Key to Flexible Bifacial Photovoltaic Applications

Kim

Shin

Lee

et al. 2020

Adv Funct Materials

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For applications to semi‐transparent and/or bifacial solar cells in building‐integrated photovoltaics and building‐applied photovoltaics, studies are underway to reduce the processing cost and time by decreasing the thickness of Cu(In1−x,Gax)Se2 (CIGSe) absorber to the ultra‐thin scale (≤500 nm). To dynamically and affordably meet the growing demand for electric power, daylighting, and architectural aesthetics of buildings in urban area, flexible semi‐transparent ultra‐thin (F‐STUT) CIGSe solar cells are proposed on flexible ultra‐thin glass (UTG) and compared with rigid semi‐transparent ultra‐thin (STUT) CIGSe solar cells fabricated on soda‐lime glass (SLG). At all the tested deposition temperatures of CIGSe, the F‐STUT CIGSe solar cells exhibit superior performance compared to the rigid STUT CIGSe solar cells. Furthermore, through realistic measurement under ≈1.3‐sun illumination, maximum bifacial power conversion efficiency of 11.90% and 13.23% are obtained for SLG and UTG, respectively. The major advantages of using UTG instead of SLG are not only the intrinsic characteristics of UTG, such as flexibility and high transmittance, but also collateral benefits such as the larger CIGSe grain size at the deposition temperature, better CIGSe crystalline quality, more precise controllability of the alkali element, and reduced thickness of the interfacial GaOx layer, which enhance the photovoltaic parameters.

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Section: Introductionmentioning

confidence: 99%

Flexible and Semi‐Transparent Ultra‐Thin CIGSe Solar Cells Prepared on Ultra‐Thin Glass Substrate: A Key to Flexible Bifacial Photovoltaic Applications

Kim

Shin

Lee

et al. 2020

Adv Funct Materials

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“…In contrast, graded GGI compositions are observed on Mo back contacts, with a steeper profile when the CIGS deposition temperature is decreased from 550°C to 500°C (Figure 4A,B). An increasing GGI ratio at the back interface of CIGS is known to create a back surface field that repels electrons toward the front interface 7 . Hence, the deposition of ultrathin CIGS at 500°C and subsequent steeper GGI back grading should reduce nonradiative recombination at the CIGS rear interface.…”

Section: Resultsmentioning

confidence: 99%

Interface engineering of ultrathin Cu(In,Ga)Se₂ solar cells on reflective back contacts

Gouillart

Cattoni

Chen

et al. 2020

Progress in Photovoltaics

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Cu(In,Ga)Se2‐based (CIGS) solar cells with ultrathin (≤500 nm) absorber layers suffer from the low reflectivity of conventional Mo back contacts. Here, we design and investigate ohmic and reflective back contacts (RBC) made of multilayer stacks that are compatible with the direct deposition of CIGS at 500°C and above. Diffusion mechanisms and reactions at each interface and in the CIGS layer are carefully analyzed by energy dispersive X‐ray (EDX)/scanning transmission electron microscopy (STEM). It shows that the highly reflective silver mirror is efficiently encapsulated in ZnO:Al layers. The detrimental reaction between CIGS and the top In2O3:Sn (ITO) layer used for ohmic contact can be mitigated by adding a 3 nm thick Al2O3 layer and by decreasing the CIGS coevaporation temperature from 550°C to 500°C. It also improves the compositional grading of Ga toward the CIGS back interface, leading to increased open‐ circuit voltage and fill factor. The best ultrathin CIGS solar cell on RBC exhibits an efficiency of 13.5% (+1.0% as compared to our Mo reference) with a short‐circuit current density of 28.9 mA/cm2 (+2.6 mA/cm2) enabled by double‐pass absorption in the 510 nm thick CIGS absorber. RBC are easy to fabricate and could benefit other photovoltaic devices that require highly reflective and conductive contacts subject to high temperature processes.

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“…Theoretically, a 500 nm Cu(In,Ga)Se 2 (CIGSe) solar cell allows more than 20% efficiency. [ 1–4 ] However, this requires a very low back contact recombination velocity and advanced optical light management. The standard molybdenum back contact is generally attributed with a high recombination velocity [ 5–7 ] and has a poor optical reflectivity.…”

Section: Introductionmentioning

confidence: 99%

Ultrathin CIGSe Solar Cells with Integrated Structured Back Reflector

et al. 2020

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Reducing the thickness of thin-film solar cells reduces the total cost of ownership of solar module production. Theoretically, a 500 nm Cu(In,Ga)Se 2 (CIGSe) solar cell allows more than 20% efficiency. [1-4] However, this requires a very low back contact recombination velocity and advanced optical light management. The standard molybdenum back contact is generally attributed with a high recombination velocity [5-7] and has a poor optical reflectivity. [8] In ref. [9], a ZrN layer on top of molybdenum having a reflectivity of 60% was used with the result of increased quantum efficiency at long wavelengths. An even higher reflectivity and higher gain in photocurrent could be achieved by an Au back reflector applied by post-deposition recontacting after removing the Mo layer. [10] In addition to cost aspects, Au is not suitable for direct deposition of CIGSe thin films at high temperatures due to the chemical reactivity with the chalcogen species during CIGSe deposition. The latter is also true for other highly reflective metals such as Ag, Cu, and Al. [11] Instead, these metals have to be encapsulated by a transparent and conductive diffusion barrier layer. Bissig et al. investigated an Al/InZnO back contact for solar cells with an absorber thickness of 2.1 μm and were able to increase the short-circuit density up to 1.4 mA cm À2 compared with a sample with Mo back contact, despite the relatively high absorber thickness. [12] According to former work on transparent back contacts, the transparent conductor indium-tin-oxide (ITO) is a good candidate as a transparent back contact [13] and as a diffusion barrier. [14] Recently, ref. [15] showed an experimental gain in short-circuit current density of 4.9 mA cm À2 in a structure Mo/Ag/ITO/0.5 μm CIGSe with respect to the reference structure of Mo/0.5 μm CIGSe. Al/ITO-based solar cells can be prepared up to at least 600 C without Al diffusion inside the absorber while providing high reflectivity at long optical wavelengths. [16] This raises the question of the electronic properties of the ITO/CIGSe contact. Keller et al. investigated 650 nm CIGSe bifacial solar cells with a hydrogen-doped In 2 O 3 back contact [17] and quantified the back-contact recombination velocity to the range of 10 7 cm s À1. This value dropped by application of an Al 2 O 3 þ NaF precursor layer stack as confirmed by a strongly increased rear-side external quantum efficiency (EQE) at short wavelengths. Unfortunately, the 5 nm Al 2 O 3 conformal layer reduces the fill factor (FF). [17] Although a flat optical reflector enhances the long-wavelength EQE upon front-side illumination to some extent, light scattering is required in addition to approach the Yablonovitch limit. [18] Yin et al. used ITO as transparent back contact and applied both dielectric SiO 2 nanoparticles on top of ITO and an external Ag mirror behind the substrate glass achieving a very high short-circuit current density of 32.4 mA cm À2 with an absorber thickness of only 390 nm. [19] This was an important step toward a structured an...

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Efficiency increased to 15.2% for ultra‐thin Cu(In,Ga)Se₂ solar cells

Cited by 51 publications

References 25 publications

Flexible and Semi‐Transparent Ultra‐Thin CIGSe Solar Cells Prepared on Ultra‐Thin Glass Substrate: A Key to Flexible Bifacial Photovoltaic Applications

Flexible and Semi‐Transparent Ultra‐Thin CIGSe Solar Cells Prepared on Ultra‐Thin Glass Substrate: A Key to Flexible Bifacial Photovoltaic Applications

Interface engineering of ultrathin Cu(In,Ga)Se₂ solar cells on reflective back contacts

Ultrathin CIGSe Solar Cells with Integrated Structured Back Reflector

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Efficiency increased to 15.2% for ultra‐thin Cu(In,Ga)Se2 solar cells

Cited by 51 publications

References 25 publications

Flexible and Semi‐Transparent Ultra‐Thin CIGSe Solar Cells Prepared on Ultra‐Thin Glass Substrate: A Key to Flexible Bifacial Photovoltaic Applications

Flexible and Semi‐Transparent Ultra‐Thin CIGSe Solar Cells Prepared on Ultra‐Thin Glass Substrate: A Key to Flexible Bifacial Photovoltaic Applications

Interface engineering of ultrathin Cu(In,Ga)Se2 solar cells on reflective back contacts

Ultrathin CIGSe Solar Cells with Integrated Structured Back Reflector

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Product

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Efficiency increased to 15.2% for ultra‐thin Cu(In,Ga)Se₂ solar cells

Interface engineering of ultrathin Cu(In,Ga)Se₂ solar cells on reflective back contacts