Elsevier

Solar Energy

Volume 145, 15 March 2017, Pages 42-51
Solar Energy

Selective thin film synthesis of copper-antimony-sulfide using hybrid ink

https://doi.org/10.1016/j.solener.2016.12.048Get rights and content

Highlights

  • The Cu-Sb-S phase has shown suitable characters as an absorber in solar cell.

  • Until now, Cu-Sb-S nanocrystals have been mostly investigated.

  • Thin films of Cu-Sb-S (CuSbS2, Cu3SbS3, Cu3SbS4, Cu12Sb4S13) were formed.

  • Different sulfurization conditions were required using a non-vacuum hybrid ink.

Abstract

In the copper-antimony-sulfide (Cu-Sb-S) system, four major phases (CuSbS2, Cu3SbS3, Cu3SbS4, Cu12Sb4S13) exist and are known to have good potentials as absorbers. To form thin films of Cu-Sb-S using a non-vacuum hybrid ink, Cu and Sb precursors were coated and sulfurized with a rapid thermal annealing (RTA) process. According to the ratio of Cu and Sb (Cu/Sb), different Cu-Sb-S thin films (CuSbS2 vs. Cu3SbS3, Cu3SbS4, Cu12Sb4S13) were easily obtained and confirmed by X-ray diffraction (XRD). However, although the Cu/Sb ratio of the hybrid ink was the same, different phases (Cu3SbS3, Cu3SbS4, Cu12Sb4S13) were observed depending on the reaction temperature, time, and pressure. It was shown that the reaction temperature, time, and pressure were also important factors for obtaining thin films. The sulfurized conditions to achieve thin films with a target phase were compared against different Cu/Sb ratios, reaction temperatures, reaction times, and chamber pressures.

Introduction

Copper-based semiconducting chalcogenides have been investigated to address the needs in a wide range of research areas, such as capacitors (Ramasamy et al., 2015) and solar cells (Jackson et al., 2011). In particular, in the photovoltaic research area, Cu(In,Ga)Se2 (CIGS) and Cu2ZnSnSe4 (CZTS) compounds are well-known because CIGS absorbers have reported efficiencies of over 21% (Clean Technica, 2014) using vacuum-based processes (co-evaporation). However, due to the high production costs and toxic material waste from vacuum-based processes, CIGS and CZTS absorbers using non-vacuum processes have also been studied despite their low conversion efficiencies. This environmental-friendly research approach using low-cost and easily accessible processes has accelerated the search for potential photovoltaic absorbers meeting specific requirements.

In recent years, ternary copper-antimony-sulfide (Cu-Sb-S) materials have received significant attention in solar cell research as alternative absorbers due to their low-toxicity and earth-abundant elements (Tablero, 2014, Yu et al., 2013, Ramasamy et al., 2014) instead of doping Sb to CIGS or SnS (Garskaite et al., 2012, Ali et al., 2015). Cu-Sb-S compounds consist of four phases, i.e., CuSbS2 (chalcostibite), Cu3SbS3 (skinnerite and wittichenite), Cu3SbS4 (famatinite), and Cu12Sb4S13 (tetrahedrite), and have high absorption coefficients (Yu et al., 2013), as well as suitable band gaps as absorbers (Yu et al., 2013, Ramasamy et al., 2014).

The band gaps of CuSbS2, Cu3SbS3, Cu3SbS4 are known to be 1.38–1.56 eV, 1.60–1.89 eV, 0.46–0.98 eV, respectively (Rodriguez-Lazcano et al., 2005, Yu et al., 2013, Tablero, 2014). On the other hand, the band gap of Cu12Sb4S13 is unclear because of the multiplicity of cation and anion sites in the structure. Cu12Sb4S13 can be represented by (Cu+)10(Cu2+)2Sb4S13 with mixed Cu(I)/Cu(II) ions (Ramasamy et al, 2014), differing from other compounds with only the Cu(I) ion. However, this mixed Cu(I)/Cu(II) ion ratio in Cu13Sb4S12 can be changed; thus, the band gap of Cu12Sb4S13 is affected due to the variation of the number of valence electrons per unit cell (Jeanloz and Johnson, 1984). According to previously reported papers, the band gap of Cu13Sb4S12 is 1.6–1.9 eV (Jeanloz and Johnson, 1984, Ramasamy et al., 2014, Tablero, 2014).

In terms of the chemical composition, CuSbS2 is different from Cu3SbS3, Cu3SbS4, and Cu12Sb4S13. Using CuSbS2 as an absorber has been actively studied (Septina et al., 2014, Yang et al., 2014, Choi et al., 2015), and conversion efficiencies have been investigated because it has a relatively optimal band gap and similar cell parameters to the well-known CIGS absorber. Recently, over 3% conversion efficiencies have been reported in CuSbS2 devices created from low-cost and environmental-friendly non-vacuum processes (Banu et al., 2016, Septina et al., 2014). However, most of the research on other Cu-Sb-S systems have only focused on material synthesis and non-performance related characterizations even though their material characters show enough potential to be absorbers.

Until now, nanoparticles of Cu-Sb-S phases have been mainly synthesized as materials for characterization (van Embden et al., 2013, Ikeda et al., 2014, Ramasamy et al., 2014); the thin film fabrication of these materials with a non-vacuum process has rarely been studied. Therefore, the fabrication of Cu-Sb-S thin films using non-vacuum hybrid ink can lead to possible applications in thin film solar cell devices. Previously, we have set up the concept of hybrid ink and showed its ability to form dense thin layers (Cho et al., 2012, Cho et al., 2013, Cho et al., 2014). In the hybrid ink, the chelating agent plays a key role to form a layer. Therefore, the complex formation of a metal precursor and the chelating agent decides whether the ink is a hybrid ink or not, to generate dense layers.

In this work, Cu and Sb precursors were used with a chelating agent to prepare a hybrid ink, and the Cu/Sb ratio was controlled in preparing each Cu-Sb-S phase (CuSbS2 vs. Cu3SbS3, Cu3SbS4, Cu12Sb4S13). After coating, these phases were sulfurized using a rapid thermal annealing (RTA) process with different reaction temperatures, reaction times, and chamber pressures to form thin films of each Cu-Sb-S phase. As a result, each phase was characterized and compared to determine the optimal conditions for thin film formation.

Section snippets

Reagents

For preparing the hybrid ink, copper(I) acetate (Cu(CH3COO) or Cu(Ac), 99.97%, Aldrich), antimony acetate (Sb(CH3COO)3 or Sb(Ac)3, 99.99%, Aldrich), methanol (CH3OH or MeOH, 99.6%, Junsei), and monoethanolamine (NH2CH2CH2OH, MEA, 99.0%, Aldrich) were used as the analytical reagents. All chemicals were used as received without further purification and stored in a nitrogen-filled glove box to prevent air or humidity from inducing degradation. The sulfur (S) powder (99.98%) for sulfurization was

Results and discussion

According to our previous work (Cho et al., 2012, Cho et al., 2013, Cho et al., 2014), the metal-chelate complex in the ink was what made the hybrid ink unique because it can control the reaction rate to make dense thin layers. To be used as a chelating agent, it should be able to not only hold precursors but should also be able to set them free for allowing them to participate in the thin layer formation during the reaction. Therefore, weak chelating agents were potential candidates to be used

Conclusions

Thin films of Cu-Sb-S phases (CuSbS2, Cu3SbS3, Cu3SbS4, Cu12Sb4S13) were formed at different sulfurization temperatures, times, pressures, and Cu/Sb ratios of the hybrid ink. Although the Cu-Sb-S phase has shown quite suitable characteristics as an absorber in solar cells, only its nanocrystal synthesis has been mainly investigated, and the formation of thin films has rarely been examined. Using a hybrid ink with a Cu/Sb ratio less than 1, dense CuSbS2 thin films were formed at 450 °C for 30 min

Acknowledgments

This study was conducted under the framework of the Research and Development Program of the Korea Institute of Energy Research (KIER) (B6-2487).

References (25)

  • A. Cho et al.

    A chelating effect in hybrid inks for non-vacuum processed CuInSe2 thin films

    J. Mater. Chem. A

    (2014)
  • Clean Technica, 2014....
  • Cited by (15)

    • Copper-based ternary metal sulfide nanocrystals embedded in graphene oxide as photocatalyst in water treatment

      2020, Nanotechnology in the Beverage Industry: Fundamentals and Applications
    • Phase transition behavior and defect analysis of CuSbS<inf>2</inf> thin films for photovoltaic application prepared by hybrid inks

      2019, Solar Energy
      Citation Excerpt :

      Over the decades, earth-abundant, cost-efficient, and environmentally friendly constituent absorber materials have attracted significant interest as substitutes of commercialized chalcogenide based Cu(InGa)Se2 (CIGS) and CdTe thin-film solar cells. For the design of earth-abundant photovoltaics (PV) with environmentally friendly and inexpensive constituents, a wide variety of research has been carried out on absorber materials, such as CuSbS2 (Cho et al., 2017), Fe2S (Berry et al., 2012; Moon et al., 2014), Sb2S3 (Chen et al., 2017), SnS (Banu et al., 2017; Sinsermsuksakul et al., 2014), and Cu2SnS3 (Tiwari et al., 2017), that contain earth-abundant and low-toxicity constituent materials with simpler structures. Among these, CuSbS2 (CAS) has attracted attention as a promising solar cell absorber material because it is environmentally friendly, cost efficient, has earth abundant materials and suitable optoelectronic properties for thin-film solar cells.

    • The effect of metal-chelate complex in Cu<inf>2</inf>SnS<inf>3</inf> thin film solar cells and their characteristics, photovoltaic performance, and defect analysis

      2019, Solar Energy
      Citation Excerpt :

      However, even though the process cost was decreased by changing from a high-cost vacuum process and rare elements to a low-cost non-vacuum process and abundant elements, the complexity of quaternary compounds and the use of toxic hydrazine are obstacles to overcome. Therefore, to address the shortcomings of these materials, the photovoltaic properties of nontoxic binary or ternary chalcogenides, such as Fe2S, Cu2S, SnS, CuSbS2, and Cu2SnS3, have been observed (Banu et al., 2017, 2016; Cho et al., 2016, 2013c; Ginley et al., 2013; Limpinsel et al., 2012; Lokhande et al., 2016; Seefeld et al., 2010; Sinsermsuksakul et al., 2013; Tiwari et al., 2014a; Wu et al., 2008). In these studies of candidate materials, ternary copper-tin-sulfide (Cu-Sn-S) materials have emerged as new alternative absorbers for thin-film solar cells.

    • Effect of Cu content in CuSbS<inf>2</inf> thin films using hybrid inks: Their photovoltaic properties and defect characteristics

      2019, Solar Energy Materials and Solar Cells
      Citation Excerpt :

      In addition, study of the sulfurization pressure showed that dense CuSbS2 thin films could be formed by optimizing the pressure [6]. Therefore, in this study, CuSbS2 thin films with different Cu compositions were fabricated using the optimum sulfurization conditions obtained previously [5,6], that is, 450 °C sulfurization temperature for 30 min reaction time at 1.02 atm. Fig. S1 shows planar and cross-sectional SEM images of as-deposited CAS films (before sulfurization) corresponding to samples CAS – 1.5, CAS – 1.2, CAS – 1 and CAS – 0.8.

    View all citing articles on Scopus
    View full text