Device Characteristics of CZTSSe Thin‐Film Solar Cells with 12.6% Efficiency

We report on the use and effect of the alkali elements rubidium and caesium in the place of sodium and potassium in the alkali post deposition treatment (PDT) as applied to Cu(In,Ga)Se2 (CIGS) solar cell absorbers. In order to study the effects of the different alkali elements, we have produced a large number of CIGS solar cells with high efficiencies resulting in a good experimental resolution to detect even small differences in performance. We examine the electrical device parameters of these fully functional devices and observe a positive trend in the I –V parameters when moving from devices without PDT to KF-, RbF-, and eventually to CsF-PDT. A diode analysis reveals an improved diode quality for cells treat-ed with heavier alkalis. Furthermore, secondary ion mass spectrometry (SIMS) measurements reveal a competitive mechanism induced within the class of alkali elements in the CIGS absorber induced by the alkali post deposition treatment. (© 2016 WILEY-VCH Verlag GmbH &Co. KGaA, Weinheim)

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Effects of heavy alkali elements in Cu(In,Ga)Se2 solar cells with efficiencies up to 22.6%

Solar Cell Efficiency Tables (Version 39)

Thin-film photovoltaic devices based on chalcopyrite Cu(In,Ga)Se2 (CIGS) absorber layers show excellent light-to-power conversion efficiencies exceeding 20%. This high performance level requires a small amount of alkaline metals incorporated into the CIGS layer, naturally provided by soda lime glass substrates used for processing of champion devices. The use of flexible substrates requires distinct incorporation of the alkaline metals, and so far mainly Na was believed to be the most favourable element, whereas other alkaline metals have resulted in significantly inferior device performance. Here we present a new sequential post-deposition treatment of the CIGS layer with sodium and potassium fluoride that enables fabrication of flexible photovoltaic devices with a remarkable conversion efficiency due to modified interface properties and mitigation of optical losses in the CdS buffer layer. The described treatment leads to a significant depletion of Cu and Ga concentrations in the CIGS near-surface region and enables a significant thickness reduction of the CdS buffer layer without the commonly observed losses in photovoltaic parameters. Ion exchange processes, well known in other research areas, are proposed as underlying mechanisms responsible for the changes in chemical composition of the deposited CIGS layer and interface properties of the heterojunction.

Potassium-induced surface modification of Cu(In,Ga)Se2 thin films for high-efficiency solar cells

The highest efficiencies in solution-processable perovskite-based solar cells have been achieved using an electron collection layer that requires sintering at 500 °C. This is unfavorable for low-cost production, applications on plastic substrates, and multijunction device architectures. Here we report a low-cost, solution-based deposition procedure utilizing nanocomposites of graphene and TiO2 nanoparticles as the electron collection layers in meso-superstructured perovskite solar cells. The graphene nanoflakes provide superior charge-collection in the nanocomposites, enabling the entire device to be fabricated at temperatures no higher than 150 °C. These solar cells show remarkable photovoltaic performance with a power conversion efficiency up to 15.6%. This work demonstrates that graphene/metal oxide nanocomposites have the potential to contribute significantly toward the development of low-cost solar cells.

http://www.am-institute.ch/assets/files/Reprints/nl403997a.pdf

Low-temperature processed electron collection layers of graphene/TiO2 nanocomposites in thin film perovskite solar cells.

In this contribution, we present a new certified world record efficiency of 20.1 and 20.3% for Cu(In,Ga)Se2 thin-film solar cells. We analyse the characteristics of solar cells on such a performance level and demonstrate a high degree of reproducibility. Copyright © 2011 John Wiley & Sons, Ltd.

New world record efficiency for Cu(In,Ga)Se2 thin‐film solar cells beyond 20%

We report on the interaction between intentional potassium doping of thin film Cu(In,Ga)Se2 (CIGS) solar cells, CIGS absorber composition, and device efficiency. Up to now high efficiency CIGS solar cells could not be produced with a gallium/(gallium + indium) ratio higher than 35%. The new doping process step does not only increase solar cell conversion efficiencies up to 20.8%, but also allows a shift in the CIGS absorber composition towards higher gallium content whilst maintaining this high efficiencies level. We find that the saturation of the open circuit voltages for higher gallium content that is normally observed can partially be overcome by the new doping procedure. This observation leads us to the conclusion that even on this high performance level CIGS solar cells still hold a potential for further development beyond the record values reported here. (© 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Compositional investigation of potassium doped Cu(In,Ga)Se2 solar cells with efficiencies up to 20.8%

Cover Picture: Compositional investigation of potassium doped Cu(In,Ga)Se2 solar cells with efficiencies up to 20.8% (Phys. Status Solidi RRL 3/2014)

We report on a new chemical bath deposition kinetics for the zinc sulfide oxide Zn(S,O) buffer layer as used in Cu(In,Ga)Se2 (CIGS)-based solar cells. The new approach allows at high rates a better control of the growth kinetics, the step coverage on the rough CIGS surface, and the [S]/([S]+[O]) ratio in the film. Layer thicknesses as needed for buffer layer applications can be grown at moderate temperatures of 60–80 °C within 5–8 min. Applying this high-rate Zn(S,O) buffer in CIGS/Zn(S,O)/(Zn,Mg)O/ZnO:Al devices, we realized highly efficient small area solar cells, 30 × 30 cm2 submodules, and 60 × 120 cm2 full-size modules. Copyright © 2012 John Wiley & Sons, Ltd.

Wiltraud Wischmann

Papers

New world record efficiency for Cu(In,Ga)Se2 thin‐film solar cells beyond 20%

Compositional investigation of potassium doped Cu(In,Ga)Se2 solar cells with efficiencies up to 20.8%

Cover Picture: Compositional investigation of potassium doped Cu(In,Ga)Se2 solar cells with efficiencies up to 20.8% (Phys. Status Solidi RRL 3/2014)

New reaction kinetics for a high‐rate chemical bath deposition of the Zn(S,O) buffer layer for Cu(In,Ga)Se2‐based solar cells

High-efficiency Cu(In,Ga)Se2 cells and modules