Abstract
Cu2ZnSnS4 is a promising, versatile and inexpensive quaternary semiconductor with suitable optoelectronic properties for solar energy conversion. In this work, we report the synthesis of CZTS nanocrystals (NCs) using low-cost homemade hot-injection method. Oleylamine was used as both the binder and stabilizer for the CZTS NCs during the growth process. Detailed investigation of the influence of sulphur concentration and reaction temperature on the structural, stoichiometric, morphological, and optoelectronic attributes of CZTS NCs was carried out. The XRD, Raman, and TEM measurements confirm the formation of phase-pure tetragonal kesterite CZTS NCs. The synthesized CZTS NCs exhibit particle sizes in the range of 15–30 nm and display strong optical absorption in the visible region. The nearly optimal chemical composition of the CZTS NCs was confirmed by energy dispersive X-ray spectroscopy. UV–Visible spectroscopy and electrochemical measurements predict the band gap of the CZTS NCs in the range of 1.3–1.6 eV, which is very close to the optimum values for the fabrication of single junction solar cells. The estimated conduction band offset (CBO) and valence band offset (VBO) of the CZTS-3M/CdS heterostructure are predicted as 0.11 and 0.98 eV, respectively, whereas for CZTS-225 °C/CdS heterostructure, CBO and VBO are 0.10 and 1.0 eV, respectively. The small conduction band offset measured at the CZTS/CdS interface are encouraging characteristics for the carrier transport and the deeper understating of band alignment and interface properties provides a hopeful approach for designing higher efficiency and more efficient carrier separation in CZTS solar cells.
Highlights
Photovoltaic (PV) technology, which makes use of the superabundant and freely available Sun’s energy to generate electricity, has obvious economic, environmental and societal benefits
The X-ray diffraction (XRD) patterns of the CZTS NCs synthesized at different sulphur concentrations (1e5 M) and reaction temperatures (200 Ce300 C) respectively, are shown in Fig. 1 (a) and 1 (b)
The variation in crystallite size of the synthesized CZTS NCs are calculated by measuring the full-width half maxima (FWHM) corresponding to (112) planes using the Debye-Scherrer formula [43]
Summary
Photovoltaic (PV) technology, which makes use of the superabundant and freely available Sun’s energy to generate electricity, has obvious economic, environmental and societal benefits. Kesterite-CZTS compounds are ideally positioned as a generation PV materials because they combine: (i) near optimum direct bandgaps (1.5 eV for CZTS and 1.13 eV for CZTSSe), (ii) high optical absorption coefficient of ~104 cmÀ1 in the visible light region, with predicted theoretical power conversion efficiency (PCE) more than 30% [9,13], and (iii) component elements that are earth-abundant, cheap, and non-toxic These characteristics make CZTS absorbers promising candidates for scalable production of cost-effective and environment-friendly thin-film photovoltaics [14e16]. The structural, morphological, and opto-electrical properties of CZTS NCs synthesized by the hot injection method can be controlled by optimizing synthesis parameters such as process temperature, injection temperature, reaction time, precursor concentrations etc In this communication, we report the successful synthesis of high-quality CZTS NCs in oleylamine (OLA) via the hot injection method. The study provides further understanding of the versatility of CZTS, not just as a traditional absorber layer, but as a charge transport layer
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