Improving the Open Circuit Voltage through Surface Oxygen Plasma Treatment and 11.7% Efficient Cu<sub>2</sub>ZnSnSe<sub>4</sub> Solar Cell

Tampo, Hitoshi; Kim, Shinho; Nagai, Takehiko; Shibata, Hajime; Niki, Shigeru

doi:10.1021/acsami.9b01756

Cited by 41 publications

(32 citation statements)

References 42 publications

(62 reference statements)

Supporting

Mentioning

Contrasting

Order By: Relevance

“…Some of the important contributing factors to the success of CIGS solar cells are the possibility of bandgap profiling with In/Ga or S/Se compositional gradients and low density of detrimental bulk defects . CZTSSe is still limited to a reported efficiency of 12.6% even though several groups have recently reached 11–12% efficiency using different fabrication routes . In this work, alloying of Cu 2 ZnSnS 4 (CZTS) with Ge and the formation of a bandgap gradient are studied as potential routes for increased efficiency.…”

Section: Introductionmentioning

confidence: 99%

Germanium Incorporation in Cu₂ZnSnS₄ and Formation of a Sn–Ge Gradient

Saini

Larsen

Sopiha

et al. 2019

Physica Status Solidi (a)

View full text Add to dashboard Cite

Alloying of Cu2ZnSnS4 (CZTS) with Ge can potentially promote grain growth and suppress the formation of Sn‐related defects. Herein, a two‐step fabrication route based on compound co‐sputtering and sulfurization at a high temperature is used to prepare Ge‐incorporated CZTS (Cu2ZnGexSn1 − xS4 [CZGTS]). For Cu2ZnGeS4 (CZGS), films deposited using elemental Ge and binary GeS targets are compared. The recrystallization is shown to be promoted for the absorbers deposited using Ge target, possibly due to lower sulfur content in the precursor suppressing the formation of wurtzite‐like phases during sputtering. The grain growth and crystallinity in CZGTS are slightly improved for x = 0.2 but not for higher concentration of the incorporated Ge. Owing to the composition‐dependent electronic properties, compositionally graded CZGTS films may be beneficial for reducing recombination towards the back contact. Hence, herein, the successful formation of a steep concentration gradient with Ge and Sn is demonstrated by the deposition of a CZGS/CZTS precursor stack followed by sulfurization with varying time periods.

show abstract

Section: Introductionmentioning

confidence: 99%

Germanium Incorporation in Cu₂ZnSnS₄ and Formation of a Sn–Ge Gradient

Saini

Larsen

Sopiha

et al. 2019

Physica Status Solidi (a)

View full text Add to dashboard Cite

show abstract

“…Ge‐incorporated Cu 2 Zn(Sn 1– x Ge x )Se 4 (CZTGSe) with kesterite crystal structure has attracted attention as a material for p‐type light absorbers in heterojunction solar cells . This is because the bandgap energy ( E g ) can be tuned from 1.0 to 1.4 eV by adjusting the cationic mixing ratios {Ge/(Ge + Sn) = x } from 0 to 1 .…”

mentioning

confidence: 99%

“…Ge-incorporated Cu 2 Zn(Sn 1-x Ge x )Se 4 (CZTGSe) with kesterite crystal structure has attracted attention as a material for p-type light absorbers in heterojunction solar cells. [1][2][3][4][5][6][7][8][9][10][11][12] This is because the bandgap energy (E g ) can be tuned from 1.0 to 1.4 eV by adjusting the cationic mixing ratios {Ge/(Ge þ Sn) ¼ x} from 0 to 1. [7,[13][14][15][16] Using this material as a light absorber, the open circuit voltage (V OC ) loss can be improved compared with that of non-Ge-incorporated Cu 2 ZnSnSe 4 (CZTSe) (x ¼ 0) [7] and large grains of polycrystalline CZTGSe in the thin film.…”

mentioning

confidence: 99%

Characterization of Surface and Heterointerface of Cu₂ZnSn_1–xGe_xSe₄ for Solar Cell Applications

Nagai

Kim

Tampo

et al. 2020

Physica Rapid Research Ltrs

Self Cite

View full text Add to dashboard Cite

This study analyzes the electronic structure of Cu2ZnSn1–xGexSe4 (CZTGSe) surface and band alignments of CdS and CZTGSe using the Ge/(Sn + Ge) composition ratios of x = 0–1 based on inversed, ultraviolet, and X‐ray photoemission spectroscopy. The conduction band offsets of the CdS/CZTGSe interface linearly decrease with increasing x, which are so‐called spike conduction band connections, whereas the valence band offsets are observed to be independent of x. Moreover, the hole density near the CZTGSe surface increases with an increase in x; this corresponds to the increase in the measured built‐in‐potential with x. However, the open circuit voltage (VOC) saturates to ≈0.5 V for x over 0.2 in spite of the favorable band alignment and larger built‐in‐potential of x at the interface. External‐quantum‐efficiency spectral analysis shows that the carrier recombination in CZTGSe bulk is suppressed with an increase in x, whereas the recombination near the CZTGSe surface is enhanced. The relationship between these recombination centers, electronic structure, and saturation of VOC is discussed.

show abstract

“…The surface recombination was found to also limit the minority carrier lifetime [124]. Tampo et al also showed V OC limitation by surface recombinations, and demonstrated suppression of surface recombinations using surface oxidation [38]. The highest conversion efficiency of 11.7% in CZTSe solar was obtained by the combination of the surface treatment and the Na doping [38].…”

Section: Alkali Dopingmentioning

confidence: 99%

“…Tampo et al also showed V OC limitation by surface recombinations, and demonstrated suppression of surface recombinations using surface oxidation [38]. The highest conversion efficiency of 11.7% in CZTSe solar was obtained by the combination of the surface treatment and the Na doping [38]. Moreover, in the pure selenium compound, Lopez-Marino et al [125] investigated different approaches for alkali doping of sequential sputtering processed CZTSe, using flexible and alkali-free substrates as is shown in figure 6.…”

Section: Alkali Dopingmentioning

confidence: 99%

Physical routes for the synthesis of kesterite

et al. 2019

Self Cite

View full text Add to dashboard Cite

This paper provides an overview of the physical vapor technologies used to synthesize Cu 2 ZnSn(S,Se) 4 thin films as absorber layers for photovoltaic applications. Through the years, CZT(S,Se) thin films have been fabricated using sequential stacking or co-sputtering of precursors as well as using sequential or co-evaporation of elemental sources, leading to high-efficient solar cells. In addition, pulsed laser deposition of composite targets and monograin growth by the molten salt method were developed as alternative methods for kesterite layers deposition. This review presents the growing increase of the kesterite-based solar cell efficiencies achieved over the recent years. A historical description of the main issues limiting this efficiency and of the experimental pathways designed to prevent or limit these issues is provided and discussed as well. A final section is dedicated to the description of promising process steps aiming at further improvements of solar cell efficiency, such as alkali doping and bandgap grading. intensive research on Cu 2 ZnSn(S,Se) 4 (CZT(S,Se)) kesterite compounds as CRM-free absorber layers for PV applications is essential. This article aims at establishing a complete overview of the physical routes used for the synthesis of kesterite thin films as absorber layers in solar cells. The following sections are devoted to that objective and will take on the main issues which have been raised so far as well as how the processes have evolved through the years to meet the requirements of the market. Some major advancements in terms of deposition or post-deposition treatments are introduced. Advantages and drawbacks of each of the physical methods presented in this review are described in detail and compared to other physical or chemical synthesis routes. Physical routes: status overviewWe performed an extensive identification of the common processes and methods used for the synthesis of kesterite thin films or for the design of solar cell devices. In order to avoid unnecessary repetitions along this paper, this section first explains these well-known and commonly used experimental processes and methods. Historically, based on the similarities between kesterite and chalcopyrite compounds, the standard device structure adopted for Cu(In,Ga)(S,Se) 2 (CIGSSe) was directly extended to CZTSSe, by simply replacing the CIGSSe absorber layer with a p-type CZTSSe thin film. CZTSSe solar cells are then typically produced using a soda-lime glass (SLG) substrate coated with a sputtered Mo layer acting as rear metallic contact. Typical sputter-deposited Mo layer thickness is around 500 nm up to 1 μm [12]. The kesterite absorber is then deposited onto the Mo layer.The fabrication of this absorber consists in the deposition of a precursor layer via a physical or a chemical route, which is then annealed in a reactive atmosphere containing either S (sulfurization) or Se (selenization). As a common result of the reactive annealing, a thin Mo(S,Se) 2 layer is naturally formed at the CZTSSe/Mo interface, betw...

show abstract

Improving the Open Circuit Voltage through Surface Oxygen Plasma Treatment and 11.7% Efficient Cu₂ZnSnSe₄ Solar Cell

Cited by 41 publications

References 42 publications

Germanium Incorporation in Cu₂ZnSnS₄ and Formation of a Sn–Ge Gradient

Germanium Incorporation in Cu₂ZnSnS₄ and Formation of a Sn–Ge Gradient

Characterization of Surface and Heterointerface of Cu₂ZnSn_1–xGe_xSe₄ for Solar Cell Applications

Physical routes for the synthesis of kesterite

Contact Info

Product

Resources

About

Improving the Open Circuit Voltage through Surface Oxygen Plasma Treatment and 11.7% Efficient Cu2ZnSnSe4 Solar Cell

Cited by 41 publications

References 42 publications

Germanium Incorporation in Cu2ZnSnS4 and Formation of a Sn–Ge Gradient

Germanium Incorporation in Cu2ZnSnS4 and Formation of a Sn–Ge Gradient

Characterization of Surface and Heterointerface of Cu2ZnSn1–xGexSe4 for Solar Cell Applications

Physical routes for the synthesis of kesterite

Contact Info

Product

Resources

About

Improving the Open Circuit Voltage through Surface Oxygen Plasma Treatment and 11.7% Efficient Cu₂ZnSnSe₄ Solar Cell

Germanium Incorporation in Cu₂ZnSnS₄ and Formation of a Sn–Ge Gradient

Germanium Incorporation in Cu₂ZnSnS₄ and Formation of a Sn–Ge Gradient

Characterization of Surface and Heterointerface of Cu₂ZnSn_1–xGe_xSe₄ for Solar Cell Applications