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Colloidal Synthesis, Optical Properties and Hole Transport Layer Applications of Cu2BaSnS4 (CBTS) Nanocrystals Rayan Chakraborty, Kyu Min Sim, Megha Shrivastava, Kumaran Nair Valsala Devi Adarsh, Dae Sung Chung, and Angshuman Nag ACS Appl. Energy Mater., Just Accepted Manuscript • DOI: 10.1021/acsaem.9b00473 • Publication Date (Web): 12 Apr 2019 Downloaded from http://pubs.acs.org on April 12, 2019
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ACS Applied Energy Materials
Colloidal Synthesis, Optical Properties and Hole Transport Layer Applications of Cu2BaSnS4 (CBTS) Nanocrystals Rayan Chakraborty,† Kyu Min Sim,§ Megha Shrivastava,¶ K. V. Adarsh¶,* Dae Sung Chung§,* Angshuman Nag†,‡,*
†Department
of Chemistry, and ‡Centre for Energy Science, Indian Institute of Science Education and Research (IISER), Pune, 411008, India
§Department
¶
of Energy Science & Engineering, Daegu Gyeongbuk Institute of Science & Technology (DGIST), Daegu 42988, Republic of Korea
Department of Physics, Indian Institute of Science Education and Research, Bhopal-462066, India
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Abstract: Cu2BaSnS4 (CBTS) is an emerging earth abundant and environmentally benign semiconductor. But there is no prior report of colloidal CBTS nanocrystals. Here we developed a colloidal synthesis of CBTS nanocrystals by rational design. Photophysical properties of these nanocrystals are elucidated using photoluminescence and ultrafast transient absorption spectroscopy. Finally, thin films of CBTS nanocrystals grown at room temperature is used as hole transport layer (HTL) in organic photodiode yielding a high peak specific detectivity (>3.2 × 1012 Jones) with low noise equivalent power (9.20 × 10-14 W Hz0.5). These results suggest that our colloidal CBTS nanocrystals have potentials for optoelectronic applications.
Table of Content:
Keywords: Metal Sulfides, Cu2BaSnS4 Nanocrystals, Colloidal Semiconductor Nanocrystals, Ultrafast Carrier Dynamics, Hole Transport Layer, Photodiode
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ACS Applied Energy Materials
Earth-abundant, environmentally benign and low-cost solution processed materials are desired for large scale optoelectronic applications. For example, Cu2ZnSn(SxSe1-x)4 (CZTSSe) and related compositions have been reported as solution processed earth abundant materials, showing solar cell efficiency of ~13%.1-3 Colloidal NCs of CZTSSe also showed interesting optoelectronic properties.4-7 But it has been found that the similarity in ionic radius (ri), and coordination number (CN), particularly between Cu and Zn gives rise to intrinsic anti-site defects (CuZn and ZnCu) in CZTSSe.8 To overcome such cationic disorder, it was suggested that the Zn2+ (ri = 0.74 Å, CN = 4) can be replaced with Ba2+ (ri = 1.56 Å, CN = 8),9 forming Cu2BaSn(SxSe1x)4
(CBTSSe) CBTSSe.10-12
Both theoretical (high defect formation energy) and experimental studies (narrow band-edge PL, lower band tailing) suggest the minimal presence of deep cation (Cu-Ba and Cu–Sn) antisite defects in CBTSSe.10-12 Early results show promising optoelectronic applications of CBTSSe with solar cell efficiency of 5.2%,12 high efficiency (~12 mA/cm2 at 0 V/RHE)13 of CBTSSe based photoelectrochemical (PEC) reduction of water to H2,14 and as hole transport layer (HTL)15 in perovskite solar cell. But one of the material design problems is poor solubility of precursors for solution processed synthesis of CBTSSe. Particularly, solution processibility of Ba precursors is limited, which probably is the main reason for the absence of prior report on colloidal synthesis of CBTS NCs. Two interesting reports emerged recently reporting molecular precursor inks to form solution processed films of CBTS.16-17 In both reports, films of molecular ink were first prepared, which were then annealed at > 350 oC giving rise to CBTS films. But till date, there is no report of forming CBTS composition dispersed in solution phase, unlike the case of colloidal CZTS NCs. Therefore, forming solution-processed films of CBTS at low temperatures (
