Effectiveness of an RbF Post Deposition Treatment of CIGS Solar Cells in Dependence on the Cu Content of the Absorber Layer

Kodalle, Tim; Bertram, Tobias; Schlatmann, Rutger; Kaufmann, Christian A.

doi:10.1109/jphotov.2019.2929418

Cited by 43 publications

(69 citation statements)

References 26 publications

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“…For small bandgap CIGSe cells with NaF and KF‐PDT, a rollover of the JV curve at low temperatures was observed, which was explained by a barrier at the Mo/CIGSe interface 26 . Kodalle et al have also reported a barrier for the photocurrent for RbF‐treated CIGSe cells 27 . But our alkali‐treated samples exhibit a different behavior; the light JV curves show a double diode behavior, that is, a clear resumption of the injection current upon higher voltage, and not any saturation of the current density, which is a behavior that has not been reported for KF‐treated CIGSe cells.…”

Section: Resultsmentioning

confidence: 98%

Effect of Na‐PDT and KF‐PDT on the photovoltaic performance of wide bandgap Cu (In,Ga)Se2 solar cells

Zahedi‐Azad

Maiberg

Scheer

2020

Progress in Photovoltaics

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Cu (In,Ga)Se 2 solar cells exhibit higher efficiencies if an appropriate Ga gradient is introduced and if the absorber is doped with sodium (Na) plus a heavier alkali atom such as potassium. However, a Gallium gradient in the presence of Na is challenging because sodium impedes the interdiffusion of elements and influences the gradient. In this contribution, we show that the presence of sodium during growth with the combination of high Ga concentration creates a pronounced gradient that is detrimental for carrier collection. One solution is to avoid Na abundance during absorber growth but to add it to the grown absorber layer via a postdeposition treatment. We investigate the effect of different Na incorporation methods simultaneously with KF-PDT on wide band gap CIGSe absorbers. By preparation on alkali-free substrates and application of alkalis (NaF and KF) onto a grown CIGSe layer, we show by smoothening of the Gallium gradient a large improvement in the solar cell performance from 4% to 8%. Another way to optimize the gradient in the presence of Na is the modification of the three-stage method. This yields the best efficiency of 10% in our laboratory at an integral GGI of 0.8. By means of temperature-dependent JV measurements, we show that the additional postdeposition of KF induces a barrier for the diode current. We conclude that KF-PDT induces a new thin layer at the CIGSe surface that has a lower valence band edge relative to the CIGSe bulk and is responsible for the double-diode behavior. This barrier can also explain the V oc (T) saturation at low temperature.

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Section: Resultsmentioning

confidence: 98%

Effect of Na‐PDT and KF‐PDT on the photovoltaic performance of wide bandgap Cu (In,Ga)Se2 solar cells

Zahedi‐Azad

Maiberg

Scheer

2020

Progress in Photovoltaics

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“…This result is consistent with other studies. 58,59 This is expected to be due to the occupation of the CIGS/Mo interface with heavier alkali metals 8 …”

Section: Resultsmentioning

confidence: 99%

Temperature‐dependent current–voltage and admittance spectroscopy analysis on cesium‐treated Cu (In_{1 − x},Ga_x)Se₂ solar cell before and after heat‐light soaking and subsequent heat‐soaking treatments

Khatri

Lin

Yashiro

et al. 2020

Progress in Photovoltaics

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Recently, we demonstrated the positive effects of heat-light soaking (HLS) and subsequent heat-soaking (HS) on cesium fluoride (CsF) treated Cu(In 1x, Ga x)Se 2 (CIGS) solar cells. However, the role of defects formation and its influence on the electronic properties have not been analyzed. With this motivation, here, we analyzed the electronic properties of CsF-free and CsF-treated CIGS solar cells before and after HLS and subsequent HS treatments using temperature-dependent current-voltage (J-V-T), admittance and low-temperature capacitance-voltage (C-V) measurements. We noticed that CsF-treated CIGS solar cells form a minority carrier trap level after HLS. The subsequent HS treatment was found to be beneficial to compensate this defect level. The admittance measurement showed a shift of the shallow energy position to a higher value after HLS and subsequent HS treatments, irrespective of Cs incorporation. This is expected to be due to the formation of a secondary diode toward the CIGS/molybdenum contact. The positive and negative effects of HLS and subsequent HS treatments on CsF-treated CIGS solar cell are discussed using low-temperature C-V measurements. By optimizing the HLS and HS processes, CsF-treated CIGS solar cells yielded total efficiencies of over 20%.

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“…[22,30] Losses in open-circuit voltage (V oc ) are not often observed and are attributed to the absence of an ordered defect compound (ODC) at the CIGS surface or a too low Cu/ (InþGa) ratio. [31,32] In this contribution, we apply alkali treatments on AlO x backpassivated solar cells and find that this combination deteriorates the solar cell performance. An injection barrier at room temperature and losses in V oc are observed.…”

Section: Introductionmentioning

confidence: 99%

Detrimental Impact of Na Upon Rb Postdeposition Treatments of Cu(In,Ga)Se₂ Absorber Layers

Wild

Birant

Eachambadi³

et al. 2021

Solar RRL

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Passivation of the Cu(In,Ga)Se 2 (CIGS)/Mo back contact using AlO x is studied to reduce the recombination at this interface. Herein, RbF postdeposition treatment (RbF-PDT), a well-established method to improve absorber and front interface properties is used on back-passivated solar cells. It is found that this combination deteriorates the performance due to formation of an injection barrier at the front and reduced acceptor concentration. Photoluminescence yield and decay times show no indication of increased defect recombination, as both are improved. With time-of-flight secondary ion mass spectroscopy, in-depth and lateral alkali profiles are measured. It is shown that the Na concentration is higher at the AlO x /Mo back contact and that Rb accumulates at the CdS/CIGS interface. It is hypothesized that Na at the back is released during the RbF-PDT and inhibits Rb diffusion into the CIGS layer. Rb remains at the front and acceptor concentration is reduced. Modeling of dark and light current-voltage characteristics shows that the injection barrier and low doping are responsible for the reduced V oc and fill factor (FF). It is suggested that the commonly observed FF losses upon heavier alkali PDT can be eliminated by adapting the initial Na amount.

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Effectiveness of an RbF Post Deposition Treatment of CIGS Solar Cells in Dependence on the Cu Content of the Absorber Layer

Cited by 43 publications

References 26 publications

Effect of Na‐PDT and KF‐PDT on the photovoltaic performance of wide bandgap Cu (In,Ga)Se2 solar cells

Effect of Na‐PDT and KF‐PDT on the photovoltaic performance of wide bandgap Cu (In,Ga)Se2 solar cells

Temperature‐dependent current–voltage and admittance spectroscopy analysis on cesium‐treated Cu (In_{1 − x},Ga_x)Se₂ solar cell before and after heat‐light soaking and subsequent heat‐soaking treatments

Detrimental Impact of Na Upon Rb Postdeposition Treatments of Cu(In,Ga)Se₂ Absorber Layers

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Effectiveness of an RbF Post Deposition Treatment of CIGS Solar Cells in Dependence on the Cu Content of the Absorber Layer

Cited by 43 publications

References 26 publications

Effect of Na‐PDT and KF‐PDT on the photovoltaic performance of wide bandgap Cu (In,Ga)Se2 solar cells

Effect of Na‐PDT and KF‐PDT on the photovoltaic performance of wide bandgap Cu (In,Ga)Se2 solar cells

Temperature‐dependent current–voltage and admittance spectroscopy analysis on cesium‐treated Cu (In1 − x,Gax)Se2 solar cell before and after heat‐light soaking and subsequent heat‐soaking treatments

Detrimental Impact of Na Upon Rb Postdeposition Treatments of Cu(In,Ga)Se2 Absorber Layers

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Temperature‐dependent current–voltage and admittance spectroscopy analysis on cesium‐treated Cu (In_{1 − x},Ga_x)Se₂ solar cell before and after heat‐light soaking and subsequent heat‐soaking treatments

Detrimental Impact of Na Upon Rb Postdeposition Treatments of Cu(In,Ga)Se₂ Absorber Layers