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Insights into kesterite's back contact interface: A status review
Karade, Vijay,Lokhande, Abhishek,Babar, Pravin,Gang, Myeng Gil,Suryawanshi, Mahesh,Patil, Pramod,Kim, Jin Hyeok North-Holland 2019 Solar Energy Materials and Solar Cells Vol. No.
<P><B>Abstract</B></P> <P>Recently, kesterite-based thin film solar cells (TFSCs) gained significant attention in the photovoltaic (PV) sector for their elemental earth abundancy and low toxicity. The emerging kesterite-based Cu<SUB>2</SUB>ZnSn(S,Se)<SUB>4</SUB> (CZTSSe) TFSCs have gained a steady rise to the record power conversion efficiency (PCE) of 12.6%, which is still significantly lower than its predecessor chalcopyrite Cu(In, Ga)Se<SUB>2</SUB> (CIGS) TFSCs. Relatively the low device efficiency in kesterite-based TFSCs is mainly observed due to the instability of back interface during the high temperature thermal annealing (HTTA) process. During the HTTA process the detrimental reactions at Mo/absorber create unsolicited defects like MoS(e)<SUB>2</SUB> layer, secondary phases and voids which consequently reduce the device efficiency. The present review offers some deep insights of the back-contact interface and interface related defects, besides different solutions to overcome these defects in detail. The interfacial-defects like the formation of MoS(e)<SUB>2</SUB> layer, secondary phases and voids at Mo/absorber interface are conversed broadly with their respective reaction mechanism. Moreover, the plausible band theory of back contact interface in the presence of interfacial MoS(e)<SUB>2</SUB> layer and the criteria for ideal back contact are also addressed. In conclusion, this review envisions the contests and perception for achieving high efficiency in kesterite based TFSCs by signifying an improvement in back interface related defects.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Recent progress and insights of kesterites back contact interface are summarized. </LI> <LI> The alteration in band alignment at Mo/absorber interface is proposed based on interfacial MoS(e)2 nature. </LI> <LI> The origin of back interface defects, respective reaction mechanisms and resolutions to overcome these defects are highlighted. </LI> <LI> The conceivable proposal for an ideal back contact interface is anticipated to achieve the high power conversion efficiency in kesterite based solar cells. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>
Effect of Precursor Composition Ratio on Surface Potential of Cu₂ZnSn(S,Se)₄ Based Absorber Layers
Vijay Karade,Jin Hyeok Kim 한국신재생에너지학회 2021 한국신재생에너지학회 학술대회논문집 Vol.2021 No.7
Solar cells based on earth abundant materials are of prime importance in PV sector for the development of sustainable energy resources. The kesterite-based photoabsorber materials Cu<sub>2</sub>ZnSn(S,Se)<sub>4</sub> (CZTSSe) have achieved the record device efficiency of 12.6%, but still it is lower than CIGS solar cell. This work we offer insights into the surface potential of the bulk and GB interfaces. To study the effect of metallic composition ratio on carrier separation process the tin (Sn) composition is varied. As the composition ratio varies the absorber morphology improves with the growth of larger grains. Further with increases in Sn content the change in the defect density observed, validated through Raman analysis. The secondary ion mass spectroscopy study demonstrated the altered distribution of sulfur (S) and sodium (Na) in CZTSSe thin films. The synergistic outcome of the increased density of defects and the accumulation of S near the interface provides a larger GB and GI difference and expedites carrier separation improvement. Subsequently, the device efficiency gets significantly improved from 6.42 to 11.04% with an open-circuit voltage (VOC) deficit of 567 mV.
Bandgap Engineering in CZTSSe Thin Films via Controlling S/(S+Se) Ratio
Vijay C. Karade,Jun Sung Jang,Kuldeep Singh Gour,Yeonwoo Park,Hyeonwook Park,Jin Hyeok Kim,윤재호 한국태양광발전학회 2023 Current Photovoltaic Research Vol.11 No.3
The earth-abundant element-based Cu2ZnSn(S,Se)4 (CZTSSe) thin film solar cells (TFSCs) have attracted greater attention in the photovoltaic (PV) community due to their rapid development in device power conversion efficiency (PCE) >13%. In the present work, we demonstrated the fine-tuning of the bandgap in the CZTSSe TFSCs by altering the sulfur (S) to the selenium (Se) chalcogenide ratio. To achieve this, the CZTSSe absorber layers are fabricated with different S/(S+Se) ratios from 0.02 to 0.08 of their weight percentage. Further compositional, morphological, and optoelectronic properties are studied using various characterization techniques. It is observed that the change in the S/(S+Se) ratios has minimal impact on the overall Cu/(Zn+Sn) composition ratio. In contrast, the S and Se content within the CZTSSe absorber layer gets altered with a change in the S/(S+Se) ratio. It also influences the overall absorber quality and gets worse at higher S/(S+Se). Furthermore, the device performance evaluated for similar CZTSSe TFSCs showed a linear increase and decrease in the open circuit voltage (Voc) and short circuit current density (Jsc) of the device with an increasing S/(S+Se) ratio. The external quantum efficiency (EQE) measured also exhibited a linear blue shift in absorption edge, increasing the bandgap from 1.056 eV to 1.228 eV, respectively.