Alkali-induced grain boundary reconstruction on Cu(In,Ga)Se2 thin film solar cells using cesium fluoride post deposition treatment

Lin, Tzu-Chun; Khatri, Ishwor; Matsuura, Junpei; Shudo, Kosuke; Huang, Wei; Sugiyama, Mutsumi; Lai, Chun‐Liang; Nakada, Tokio

doi:10.1016/j.nanoen.2019.104299

Cited by 68 publications

(77 citation statements)

References 44 publications

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“…To verify this effect on the non-sulfurized absorbers in this study, an additional reference sample (Ref_2) was produced (same CGI, GGI, and Ga profile as Ref ) and subsequently subjected to a RbF-PDT for 173 s without chalcogenide background atmosphere to ensure direct comparability. The absence of Se (or S) during Alk-PDT has previously been shown to be non-detrimental and might even be beneficial in some cases, [43,51] which is confirmed by the results for the Ref_2 sample in this study. As no intermediate S-step in a separate chamber was done, air exposure could be avoided until CdS deposition.…”

Section: Origin Of Collection Losses After Sulfurizationsupporting

confidence: 89%

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Heavy Alkali Treatment of Post‐Sulfurized Cu(In,Ga)Se₂ Layers: Effect on Absorber Properties and Solar Cell Performance

et al. 2020

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This contribution evaluates a sequential post‐deposition treatment of Cu(In,Ga)Se2 (CIGS) films, consisting of 1) a post‐sulfurization in elemental S‐atmosphere and 2) a subsequent treatment by heavy alkali fluorides (Alk‐PDT). First, the effect of the sulfurization step on the corresponding solar cell performance is investigated and optimum process parameters, leading to an efficiency improvement, are identified. Losses in carrier collection observed after S‐incorporation are attributed to an increased grain boundary (GB) recombination. It is found that the corresponding reduction in short‐circuit current density can be mitigated by a RbF‐ or KF‐PDT, supposedly by depleting GBs in Cu. However, in strong contrast to non‐sulfurized CIGS, the Alk‐PDT results in a lower open‐circuit voltage and distortions in the current–voltage (I–V) characteristics for sulfurized absorbers. Possible explanations are the absence of a wide‐gap surface phase and/or air exposure between the post‐treatment steps. It is further proposed that a back contact barrier may be responsible for the distortions in I–V.

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Section: Origin Of Collection Losses After Sulfurizationsupporting

confidence: 89%

“…Interestingly, the distortion is more severe for the Alk-PDT with the heavier alkali metal Rb. Similar behavior in I-V was reported before for too strong alkali doses [28,51,52] or if a heat-treatment is done after the PDT step. [53] Different explanations were suggested for these observations.…”

Section: Origin Of Collection Losses After Sulfurizationsupporting

confidence: 82%

Heavy Alkali Treatment of Post‐Sulfurized Cu(In,Ga)Se₂ Layers: Effect on Absorber Properties and Solar Cell Performance

et al. 2020

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“…The increased V OC was higher than that estimated from the C–V measurements. Therefore, it can be assumed that CsF‐PDT not only increases the net carrier concentration but also reduces CdS/CIGS interfacial recombination 7 and/or improve the material quality 3,4 …”

Section: Resultsmentioning

confidence: 99%

“…The incorporation of heavy alkali metals, such as potassium (K), rubidium (Rb), and cesium (Cs), into CIGS 1–13 and perovskite 14–20 solar cells are the recent hot topics in efficiency improvement. Rb‐ and Cs‐incorporated CIGS solar cells demonstrated a certified efficiency of 22.6% 2 and 23.35%, 4 respectively.…”

Section: Introductionmentioning

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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“…State‐of‐the‐art Cu(In 1– x ,Ga x )Se 2 (CIGS) solar cells are fabricated using heavy alkali metal [potassium (K), rubidium (Rb), and cesium(Cs)] postdeposition treatments (PDTs) . Several different mechanisms have been proposed for the beneficial effect of the alkali metal PDTs, such as a reduction of the Cu and Ga concentrations at the near‐surface layer, formation of dense shallow donor‐type Cd Cu during the chemical bath deposition of cadmium sulfide (CBD‐CdS) process, a reduction in thickness of the buffer layer, a shift of the valance band to lower binding energies, a surface bandgap widening, an enhancement of the hole concentration, an enhancement of the minority carrier lifetime, a reduction in potential fluctuations, the formation of new secondary compounds at the surface, mitigation of the shunting associated with high Cu content, and the passivation of grain boundaries …”

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confidence: 99%

Metastable Behavior on Cesium Fluoride‐Treated Cu(In_1–x,Ga_x)Se₂ Solar Cells

Khatri

Yashiro

Lin

et al. 2020

Physica Rapid Research Ltrs

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Metastable behavior of cesium fluoride (CsF)‐treated Cu(In1–x,Gax)Se2 (CIGS) solar cells is investigated under heat‐light soaking (HLS) and heat‐soaking (HS) treatments. HLS increases open‐circuit voltage, fill factor, efficiency, and net carrier concentration and decreases short‐circuit current density, whereas heat‐soaking treatment acts oppositely. The performance of a CsF postdeposition treatment to CIGS thin film in selenium vapor, and closer to stoichiometry copper content, did not mitigate the open‐circuit voltage improvement after HLS. These results argue the traditional concept of the VSe–VCu divacancy complex for the total beneficial effect of HLS in alkali‐treated CIGS solar cells. The metastable behavior observed in the CsF‐treated devices due to the HLS and HS treatments is explained by the specific behavior of alkali‐containing new compounds at the surface and/or the migration of alkali metals at the surface and bulk regions.

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Alkali-induced grain boundary reconstruction on Cu(In,Ga)Se2 thin film solar cells using cesium fluoride post deposition treatment

Cited by 68 publications

References 44 publications

Heavy Alkali Treatment of Post‐Sulfurized Cu(In,Ga)Se₂ Layers: Effect on Absorber Properties and Solar Cell Performance

Heavy Alkali Treatment of Post‐Sulfurized Cu(In,Ga)Se₂ Layers: Effect on Absorber Properties and Solar Cell Performance

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

Metastable Behavior on Cesium Fluoride‐Treated Cu(In_1–x,Ga_x)Se₂ Solar Cells

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Alkali-induced grain boundary reconstruction on Cu(In,Ga)Se2 thin film solar cells using cesium fluoride post deposition treatment

Cited by 68 publications

References 44 publications

Heavy Alkali Treatment of Post‐Sulfurized Cu(In,Ga)Se2 Layers: Effect on Absorber Properties and Solar Cell Performance

Heavy Alkali Treatment of Post‐Sulfurized Cu(In,Ga)Se2 Layers: Effect on Absorber Properties and Solar Cell Performance

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

Metastable Behavior on Cesium Fluoride‐Treated Cu(In1–x,Gax)Se2 Solar Cells

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Heavy Alkali Treatment of Post‐Sulfurized Cu(In,Ga)Se₂ Layers: Effect on Absorber Properties and Solar Cell Performance

Heavy Alkali Treatment of Post‐Sulfurized Cu(In,Ga)Se₂ Layers: Effect on Absorber Properties and Solar Cell Performance

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

Metastable Behavior on Cesium Fluoride‐Treated Cu(In_1–x,Ga_x)Se₂ Solar Cells