Fabrication of $$\text {Cu}_{2}\text {SnS}_{3}$$ Cu 2 SnS 3 films by annealing chemically deposited SnS-CuS precursors in a graphite box

Chalapathi, U.,Poornaprakash, B.,Park, Si-Hyun Springer-Verlag 2018 Journal of materials science. Materials in electro Vol.29 No.2

<P>Monoclinic Cu2SnS3 (CTS) thin films are prepared by annealing chemically deposited SnS-CuS precursors at 520-580 degrees C in a graphite box under atmospheric (N-2 + S-2) pressure, and the effects of annealing temperature and time on the grain growth and morphology of the films are investigated. The films prepared at 520 and 550 degrees C show improvement in grain size and the formation of uniform and compact grains with increasing annealing time. The films prepared at 580 degrees C exhibit good grain growth with grain sizes similar to 1.0-3.0 mu m; however, the grain size does not increase with annealing time. Further, annealing time of 120 min at 550 and 580 degrees C leads to material loss. A small amount of Cu4SnS4 is detected in the films. In addition, annealing the films at 550 and 580 degrees C for 90 min with decreased CuS thickness results in a reduction of Cu4SnS4 phase, homogeneous grain growth with grain sizes of 2.0-3.5 mu m throughout the film thickness, and hole mobilities in the range of 6.0-5.3 cm(2) V-1 s(-1). These results demonstrate the effectiveness of this annealing approach for producing high quality CTS films with micron-sized grains, which is useful for improving the efficiency of CTS-based thin film solar cells.</P>

Performance of CZTSSe thin film solar cells fabricated using a sulfo-selenization process: Influence of the Cu composition

Chalapathy, R.B.V.,Gang, Myeng Gil,Hong, Chang Woo,Kim, Ji Hun,Jang, Jun Sun,Yun, Jae Ho,Kim, Jin Hyeok Elsevier 2018 SOLAR ENERGY -PHOENIX ARIZONA THEN NEW YORK- Vol.159 No.-

<P><B>Abstract</B></P> <P>In this work, earth-abundant CZTSSe thin film solar cells were fabricated by sulfo-selenization of the Mo/Zn/Cu/Sn/Cu metallic precursors. The influences of morphological and compositional properties of the absorbers on performance of solar cells were investigated by tuning Cu content in the films. The Raman analysis showed that absorbers consist of a kesterite CZTSSe phase with ZnSe as a minor secondary phase. X-ray photoelectron spectroscopy (XPS) analyses revealed that the surfaces are Cu depleted and Zn enriched compared with the bulk composition of the absorbers. The results indicate that during sulfo-selenization the Cu diffused into the film and the Zn towards the film surface. The performance of the solar cells initially improved with the increasing of the Cu content and then decreased. By tuning the Cu content in the absorbers, the minority-carrier life time improved from 0.8 to 1.6 ns. The power conversion efficiency increased from 5.1 to 8.03% with fine controlling of Cu composition of the CZTSSe absorbers. The diode-ideality factors are higher than 2, suggesting an increased interfacial recombination in the devices. The high ideality-factors A and low minority carrier life times may originate from surface and bulk related defects, which in turn limits the V<SUB>oc</SUB> and the achievable high conversion efficiency for the CZTSSe thin film solar cells.</P> <P><B>Highlights</B></P> <P> <UL> <LI> CZTSSe thin film solar cells were fabricated by sulfo-selenization of sputtered metallic Mo/Zn/Cu/Sn/Cu precursors. </LI> <LI> The surface composition of the absorbers was Cu depleted and Zn rich compared to the bulk of the absorbers. </LI> <LI> The ideality factors ‘A’ over 2 suggest that increased interface recombination in the devices which reduced the open circuit voltage of the devices. </LI> <LI> By tuning the Cu content in the absorbers solar cells with conversion efficiency about 8.03% was obtained. And the best efficiency of 8.17% was achieved without an antireflection coating. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>

Large-grained Sb₂S₃ thin films with Sn-doping by chemical bath deposition for planar heterojunction solar cells

Chalapathi, U.,Poornaprakash, B.,Ahn, Chang-Hoi,Park, Si-Hyun Elsevier 2018 Materials science in semiconductor processing Vol.84 No.-

<P><B>Abstract</B></P> <P>Herein, the growth of large-grained and compact Sb<SUB>2</SUB>S<SUB>3</SUB> thin films with good electrical properties by Sn doping using a chemical bath deposition (CBD) and annealing approach is detailed. Sn-doped Sb<SUB>2</SUB>S<SUB>3</SUB> thin films were prepared using the CBD method with SbCl<SUB>3</SUB>, SnCl<SUB>2</SUB>.2H<SUB>2</SUB>O, and Na<SUB>2</SUB>S<SUB>2</SUB>O<SUB>3</SUB> as source materials, and ethylenediamine tetraacetic acid (EDTA) as the complexing agent at 40 ° C for 3 h followed by annealing at 250 °C for 30 min under Ar ambience. Un-doped Sb<SUB>2</SUB>S<SUB>3</SUB> films exhibited an orthorhombic crystal structure with lattice parameters of <I>a</I>= 1.142 nm, <I>b</I>= 0.381 nm, and <I>c</I>= 1.124 nm, crystalline grain sizes of 100 nm, a direct optical band gap of 1.70 eV, p-type electrical conductivity with high electrical resistivity, and low hole mobility. With Sn doping, a significant increase in the grain size of the films from 6 to > 10 μ m was observed with increasing Sn content from 1.0 to 5.5 at% followed by a decrease in the grain size. The direct optical band gap of the films was 1.71–1.72 eV. By varying Sn at%, the electrical resistivity of the films decreased, and hole mobility increased from 117 to 205 cm<SUP>2</SUP> V<SUP>−1</SUP> s<SUP>−1</SUP> up to 5.5 at% and decreased to 166 cm<SUP>2</SUP> V<SUP>−1</SUP> s<SUP>−1</SUP> at 7.2 at%. With the addition of 1.0–5.5 at% Sn in the Sb<SUB>2</SUB>S<SUB>3</SUB> films, the grain growth and electrical properties of the films were drastically enhanced, which is beneficial for the fabrication of planar heterojunction solar cells.</P>

Rapid growth of Sb₂S₃ thin films by chemical bath deposition with ethylenediamine tetraacetic acid additive

Chalapathi, U.,Poornaprakash, B.,Ahn, Chang-Hoi,Park, Si-Hyun Elsevier 2018 APPLIED SURFACE SCIENCE - Vol.451 No.-

<P><B>Abstract</B></P> <P>Sb<SUB>2</SUB>S<SUB>3</SUB> is a suitable photovoltaic material because of its favorable optoelectronic properties as well as being comprised of earth-abundant and nontoxic precursor elements. The chemical bath deposition method has been widely used to deposit Sb<SUB>2</SUB>S<SUB>3</SUB> thin films. However, longer deposition times as well as multiple depositions have been reported to prepare thicker Sb<SUB>2</SUB>S<SUB>3</SUB> films. In order to produce good quality Sb<SUB>2</SUB>S<SUB>3</SUB> films with a thickness greater than 1 μ m within a short deposition time, we have added a small amount of ethylenediamine tetraacetic acid (EDTA) to the conventional chemical proportions used for the deposition of Sb<SUB>2</SUB>S<SUB>3</SUB> films. The effect of EDTA, Na<SUB>2</SUB>S<SUB>2</SUB>O<SUB>3</SUB>, bath temperature, and the deposition time were studied. By optimizing these conditions, uniform good quality Sb<SUB>2</SUB>S<SUB>3</SUB> thin films with a thickness greater than 1 μ m could be obtained in a short deposition time of 3 h. The films prepared at the optimized conditions were annealed to improve the crystallinity. The films exhibited orthorhombic crystal structure with lattice parameters a = 1.142 nm, b = 0.381 nm, and c = 1.124 nm, and a direct optical band gap of 1.66 eV. This approach is beneficial for obtaining good quality Sb<SUB>2</SUB>S<SUB>3</SUB> films which is ideal for solar cell applications.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Rapid chemical bath deposition of Sb<SUB>2</SUB>S<SUB>3</SUB> thin films with EDTA complexing agent. </LI> <LI> The effects of EDTA, Na<SUB>2</SUB>S<SUB>2</SUB>O<SUB>3</SUB>, bath temperature, and deposition time were studied. </LI> <LI> Sb<SUB>2</SUB>S<SUB>3</SUB> films of thickness greater than >1 μ m were obtained on addition of small amount of EDTA. </LI> <LI> Films annealed at 250 ° C in Ar atmosphere showed improvement in crystallization. </LI> </UL> </P>

Two-stage processed CuSbS₂ thin films for photovoltaics: Effect of Cu/Sb ratio

Chalapathi, U.,Poornaprakash, B.,Ahn, Chang-Hoi,Park, Si-Hyun Elsevier 2018 CERAMICS INTERNATIONAL Vol.44 No.12

<P><B>Abstract</B></P> <P>In recent years, CuSbS<SUB>2</SUB> has attracted significant research interest because of its direct optical band gap of 1.5 eV, high optical absorption coefficient, p-type electrical conductivity, and composition involving earth-abundant and non-toxic precursor elements. We prepared CuSbS<SUB>2</SUB> thin films by annealing chemically grown Sb<SUB>2</SUB>S<SUB>3</SUB> and sputter deposited Cu (Sb<SUB>2</SUB>S<SUB>3</SUB>/Cu) stacks in a graphite box, and studied the effect of the Cu/Sb ratio on the growth and properties of these films by varying the thickness of Cu while keeping the thickness of Sb<SUB>2</SUB>S<SUB>3</SUB> constant. The Cu/Sb ratio significantly impacted the phase purity, grain growth, and morphology of the CuSbS<SUB>2</SUB> films. The CuSbS<SUB>2</SUB> films prepared with a Cu/Sb ratio of 0.78 showed some unreacted Sb<SUB>2</SUB>S<SUB>3</SUB> and nonuniform grain growth. Upon increasing the Cu/Sb ratio from 0.85 to 0.97, the Sb<SUB>2</SUB>S<SUB>3</SUB> phase was consumed completely, and phase-pure CuSbS<SUB>2</SUB> with homogeneous grain formation was obtained. These films exhibited an orthorhombic crystal structure with the (410) preferred orientation. Further increase in the Cu/Sb ratio from 1.28 to 1.52 resulted in a change in the growth direction along the (200) plane and the formation of several micron-sized grains with a compact morphology and Cu<SUB>3</SUB>SbS<SUB>4</SUB> secondary phase. The direct optical band gap of the films decreased from 1.52 to 1.48 eV when Cu/Sb ratio was increased from 0.91 to 1.28. The films exhibited p-type electrical conductivity and their electrical resistivity decreased with increasing Cu/Sb ratio. From this investigation it was clear that deviation in the Cu/Sb ratio from the stoichiometric proportion leads to inhomogeneous grain growth of CuSbS<SUB>2</SUB> films, which affect the performance of devices using these films.</P>

Growth of Cu₂ZnSnS₄ thin films by sulfurization of precursors in S vapor

Chalapathy, R.B.V.,Larina, L.,Kim, Min-Sik,Yun, Jae-Ho,Yoon, Kyung-Hoon,Ahn, Byung-Tae 한국신재생에너지학회 2007 한국신재생에너지학회 학술대회논문집 Vol.2007 No.11

Reaction Path of Cu₂ZnSnS₄ Nanoparticles by a Solvothermal Method Using Copper Acetate, Zinc Acetate, Tin Chloride and Sulfur in Diethylenetriamine Solvent

Chalapathy, R.B.V.,Jung, Gwang Sun,Ko, Young Min,Ahn, Byung Tae,Kown, HyukSang Korea Photovoltaic Society 2013 Current Photovoltaic Research Vol.1 No.2

$Cu_2ZnSnS_4$ (CZTS) nanoparticles were synthesized by a solvothermal method using copper (II) acetate, zinc acetate, tin chloride, and sulfur in diethylenetriamine solvent. Binary sulfide particles such as CuS, ZnS, SnS, and $SnS_2$ were obtained at $180^{\circ}C$; single-phase CZTS nanoparticles were obtained at $280^{\circ}C$. CZTS nanoparticles with spherical shape and grain size of 40 to 60 nm were obtained at $280^{\circ}C$. In the middle of 180 and $280^{\circ}C$, CZTS and ZnS phases were found. The time variation of reaction at $280^{\circ}C$ revealed that an amorphous state formed first instead of binary phases and then the amorphous phase was converted to crystalline CZTS state; it is different reaction path way from conventional solid-state reaction path of which binary phases react to form CZTS. CZTS films deposited and annealed from single-phase nanoparticles showed porous microstructure and poor adhesion. This indicates that a combination of CZTS and other flux phase is necessary to have a dense film for device fabrication.

Fabrication of Cu₂ZnSnS₄ Films by Rapid Thermal Annealing of Cu/ZnSn/Cu Precursor Layer and Their Application to Solar Cells

Chalapathy, R.B.V.,Jung, Gwang Sun,Ko, Young Min,Ahn, Byung Tae,Kwon, HyukSang Korea Photovoltaic Society 2013 Current Photovoltaic Research Vol.1 No.2

$Cu_2ZnSnS_4$ thin film have been fabricated by rapid thermal annealing of dc-sputtered metal precursor with Cu/ZnSn/Cu stack in sulfur ambient. A CZTS film with a good uniformity was formed at $560^{\circ}C$ in 6 min. $Cu_2SnS_3$ and $Cu_3SnS_4$ secondary phases were present at $540^{\circ}C$ and a trace amount of $Cu_2SnS_3$ secondary phase was present at $560^{\circ}C$. Single-phase large-grained CZTS film with rough surface was formed at $560^{\circ}C$. Solar cell with best efficiency of 4.7% ($V_{oc}=632mV$, $j_{sc}=15.8mA/cm^2$, FF = 47.13%) for an area of $0.44cm^2$ was obtained for the CZTS absorber grown at $560^{\circ}C$ for 6 min. The existence of second phase at lower-temperature annealing and rough surface at higher-temperature annealing caused the degradation of cell performance. Also poor back contact by void formation deteriorated cell performance. The fill factor was below 0.5; it should be increased by minimizing voids at the CZTS/Mo interface. Our results suggest that CZTS absorbers can be grown by rapid thermal annealing of metallic precursors in sulfur ambient for short process times ranging in minutes.

Two-stage processed Cu₄SnS₄ thin films for photovoltaics - Effect of (N₂ + S₂) pressure during annealing

Chalapathi, U.,Poornaprakash, B.,Park, Si-Hyun Elsevier 2018 THIN SOLID FILMS - Vol.660 No.-

<P><B>Abstract</B></P> <P>In this paper, we report the fabrication of Cu<SUB>4</SUB>SnS<SUB>4</SUB> thin films by annealing chemically deposited SnS–CuS precursors at 823 K for 90 min, and we studied the effect of the (N<SUB>2</SUB> + S<SUB>2</SUB>) pressure during annealing on the growth and properties of the Cu<SUB>4</SUB>SnS<SUB>4</SUB> films. Films prepared at a (N<SUB>2</SUB> + S<SUB>2</SUB>) pressure of 1.3 kPa exhibited an orthorhombic crystal structure with lattice parameters of a = 1.371 nm, b = 0.766 nm, and c = 0.643 nm, a grain size of 3–6 μm, a direct optical band gap of 1.0 eV, p-type electrical conductivity, and a hole mobility of 69.5 cm<SUP>2</SUP> V<SUP>−1</SUP> s<SUP>−1</SUP>. Increasing the (N<SUB>2</SUB> + S<SUB>2</SUB>) pressure from 1.3 kPa to 66.7 kPa increased the grain size to more than 6 μm and the hole mobility to 150 cm<SUP>2</SUP> V<SUP>−1</SUP> s<SUP>−1</SUP> at 26.7 kPa and then decreased to 86 cm<SUP>2</SUP> V<SUP>−1</SUP> s<SUP>−1</SUP> at 66.7 kPa. Further increasing the (N<SUB>2</SUB> + S<SUB>2</SUB>) pressure to 101.3 kPa resulted in the formation of a monoclinic Cu<SUB>2</SUB>SnS<SUB>3</SUB> secondary phase. This study reveals that an annealing temperature of 823 K and a (N<SUB>2</SUB> + S<SUB>2</SUB>) pressure of 1.3–66.7 kPa are the optimized conditions to obtain large-grained Cu<SUB>4</SUB>SnS<SUB>4</SUB> films free of secondary phases with good optical and electrical properties.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Cu<SUB>4</SUB>SnS<SUB>4</SUB> thin films were grown by annealing SnS–CuS stacks in a graphite box. </LI> <LI> The effect of (N<SUB>2</SUB> + S<SUB>2</SUB>) pressure during annealing on the growth of the films investigated </LI> <LI> (N<SUB>2</SUB> + S<SUB>2</SUB>) pressure significantly enhanced the grain growth and electrical properties of films. </LI> <LI> Large-grained Cu<SUB>4</SUB>SnS<SUB>4</SUB> films obtained at 1.3–66.7 kPa (N<SUB>2</SUB> + S<SUB>2</SUB>) pressure </LI> </UL> </P>

Effect of Eco-friendly chemical treatments on mechanical properties of Vinyl ester/Bamboo paper composites

K. Venkata Chalapathi,M.N. Prabhakar,Jung-il Song 대한기계학회 2019 대한기계학회 춘추학술대회 Vol.2019 No.5