| As a kind of ternary compound semiconductor material,Cu2SnS3(CTS)consisting of nontoxic and abundant elements is considered suitable for the absorb layer of thin film solar cell due to its appropriate band gap and high optical absorption coefficient.The record conversion efficiency of CTS-based solar cell is 4.63%,but compared to the theoretical efficiency,there is still a big gap.The poor crystal quality and high carrier concentration are the current main problems for fabricating CTS solar cel s with high efficiency.It was first proposed in this paper that preparing CTS precursors by RF magnetron sputtering Sn metal target and CuS compound target.In order to obtain the CTS thin films with good crystal quality and suitable chemical composition,the sputtering and sulfurization conditions were optimized.For comparison,the common method to prepare CTS thin films was adopted,which is sulfurizing the Cu,Sn metal precursors.The optical and electrical properties of two kinds of samples based on different precursors were investigated,and final y,the two different CTS samples were attempted to fabricate thin film solar cel s.The main research contents and results are summarized as following:(1)Sulfurizing the precursors deposited by sputtering Sn and CuS targets.The effects of different Cu/Sn ratios,varied heating rates and sulfurization temperatures on the CTS thin film characteristics were investigated.The pure phase CTS thin films with good crystal inity,compact surface and proper element composition were obtained by sulfurizing the precursors with Cu/Sn = 1.80 at temperature 570 ℃(the heating rate was 35 ℃/min).It was found that secondary phases were easy to form in CTS thin films if the sulfurization temperature was too low,high temperature could facilitate crystal grain growth,but the excessive Sn loss due to the over-high sulfurization temperature would form many holes in the films.(2)Sulfurizing the precursors deposited by sputtering Sn and Cu metal targets.The effects of different Cu/Sn ratios,varied heating rates and sulfurization temperatures on the CTS thin film characteristics were investigated.The pure phase CTS thin films with good crystal quality,compact surface,large grain size and proper element composition were obtained by sulfurizing the precursors with Cu/Sn = 1.60 at temperature 580 ℃(the heating rate was 25 ℃ /min).It was found that if the sulfurization temperature was too low,the surface of CTS thin film was rough and the crystal grain size was smal,high temperature could enlarge crystal grain size obviously,but there was a thick fine grain layer between the CTS film and substrate,namely forming double layer structure.(3)Comparing the two different kinds of samples,the crystal grain size of CTS thin film made from Sn/CuS precursor was smal er than that from Sn/Cu precursor,but the Sn loss was less during sulfurization,in addition,the optical and electrical characteristics were better.The band gap of CTS thin film made from Sn/CuS precursor was around 0.95 eV,the magnitude of carrier concentration and the average mobility were 1017–1018 cm-3 and 6 cm2V-1s-1,respectively.Whereas,for the CTS thin film made from Sn/Cu precursor,the band gap was around 0.86 eV,the magnitude of carrier concentration was 1019–1020 cm-3 and the average mobility was just 3 cm2V-1s-1.(4)The optimized CTS thin films based on different precursors were attempted to fabricate CTS thin film solar cel s(Mo/CTS/CdS/AZO/Al),and the effects of two kinds of CTS samples on device parameters were investigated.It showed that the CTS thin film solar cell made from Sn/CuS precursor obtained 1.32% conversion efficiency,but the efficiency was near zero for the solar cell made from Sn/Cu precursor,which was probably because the fine grain under absorber layer increased the recombination of carriers and series resistance of device,leading to almost no short circuit current. |
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