Jinchun Jiang

Synthesis and characterization of Cu2ZnSnS4 thin films by the sulfurization of co-electrodeposited Cu–Zn–Sn–S precursor layers for solar cell applications

Cu2ZnSnS4 (CZTS) absorbers have been successfully deposited on tin-doped indium oxide coated glass (ITO/glass) substrates by sulfurization process of co-electrodeposited Cu–Zn–Sn–S precursor thin films at various annealing temperatures ranging from 500 to 580 °C for 30 min in an atmosphere of Ar–H2S (6.5%). The effects of sulfurization temperature on the structure, morphology, composition and optical properties of CZTS thin films have been investigated in details. XRD and Raman measurements reveal that the intensity of preferential orientation along the (112) direction becomes relatively more intense and sharp with increasing annealing temperature. The morphological and chemical composition studies indicate the formation of compact and homogenous CZTS thin films with Cu-poor and Zn-rich composition at a sulfurization temperature of 560 °C. And its band gap energy is around 1.50 eV. The AZO/i-ZnO/CdS/CZTS/ITO/glass thin-film solar cell is fabricated with the CZTS absorber layer grown at an optimized sulfurization temperature of 560 °C. It shows a power conversion efficiency of 1.98% for a 0.25 cm2 area with Voc = 490 mV, Jsc = 9.69 mA cm−2 and FF = 40.03%.

Characteristics of in-substituted CZTS thin film and bifacial solar cell.

Implementing bifacial photovoltaic devices based on transparent conducting oxides (TCO) as the front and back contacts is highly appealing to improve the efficiency of kesterite solar cells. The p-type In substituted Cu2ZnSnS4 (CZTIS) thin-film solar cell absorber has been fabricated on ITO glass by sulfurizing coelectroplated Cu-Zn-Sn-S precursors in H2S (5 vol %) atmosphere at 520 °C for 30 min. Experimental proof, including X-ray diffraction, Raman spectroscopy, UV-vis-NIR transmission/reflection spectra, PL spectra, and electron microscopies, is presented for the interfacial reaction between the ITO back contact and CZTS absorber. This aggressive reaction due to thermal processing contributes to substitutional diffusion of In into CZTS, formation of secondary phases and electrically conductive degradation of ITO back contact. The structural, lattice vibrational, optical absorption, and defective properties of the CZTIS alloy absorber layer have been analyzed and discussed. The new dopant In is desirably capable of improving the open circuit voltage deficit of kesterite device. However, the nonohmic back contact in the bifacial device negatively limits the open circuit voltage and fill factor, evidencing by illumination-/temperature-dependent J-V and frequency-dependent capacitance-voltage (C-V-f) measurements. A 3.4% efficient solar cell is demonstrated under simultaneously bifacial illumination from both sides of TCO front and back contacts.

Cu2ZnSnS4 thin film solar cell utilizing rapid thermal process of precursors sputtered from a quaternary target: a promising application in industrial processes

Cu2ZnSnS4 (CZTS) thin films have been attracting considerable attention as candidates for new photovoltaic materials. As a typical vacuum process, a sputtering stacked metallic layer followed by a conventional slow thermal process (STP) is usually used. This method is complex and time-consuming. Furthermore, the volatilization of Zn and Sn elements is significant during the STP process. To simplify the CZTS fabrication process and solve the element volatilization problem, in this work CZTS thin film was fabricated using a single quaternary target Radio-Frequency (RF) magnetron sputtering process followed by a rapid thermal process (RTP). The effects of sulfurization temperature on the properties of CZTS thin films have been studied. The compositional analysis shows that a combination of a single target sputtering process and the RTP technique can significantly reduce the volatilization of Zn and Sn elements compared to the conventional STP process. The results of X-ray diffraction (XRD) patterns and Raman scatting spectra show that the sulfurized CZTS thin films have a polycrystalline kesterite crystal structure. If the sulfurization process is performed at lower temperature, a large amount of disorder among the Cu and Zn cations exists in the CZTS thin film which is investigated by using Raman scattering spectra. At 550 °C, the CZTS thin film has high quality of crystallinity with large grain size and dense morphology, its band gap energy is found to be 1.53 eV. The solar cell fabricated with the CZTS absorber grown at an optimized sulfurization temperature of 550 °C shows a conversion efficiency of 2.85% for a 0.16 cm2 area with Voc = 412 mV, Jsc = 17.9 mA cm−2, and FF = 40.5%. These results show that this process is suitable for the growth of kesterite CZTS solar cell absorbers.

Co-electroplated Kesterite Bifacial Thin-Film Solar Cells: A Study of Sulfurization Temperature

Kesterite bifacial thin film solar cells using transparent conductive oxides (TCO) as front and rear back contact were prepared by the post-chalcogenation of co-electroplated Cu-Zn-Sn-S precursors. The crystallization growth machnism of kesterite materials on the ITO and FTO substrates are investigated. A novel interfacial reaction between ITO and kesterite materials is revealed. 5% efficient kesterite sulfide bifacial solar cells are achieved under front-side illumination.

Co-electroplated Cu 2 ZnSnS 4 thin-film solar cells: The role of precursor metallic composition

Thin film solar cells with a structure of ZnO/CdS/Cu2ZnSnS4 (CZTS)/Mo were fabricated successfully by sulfurization of co-electroplated Cu-Zn-Sn-S precursors with different metallic compositions. The best solar cell performance with an efficiency of 5.5% was achieved from a slightly Zn-rich and Sn-/Cu-poor (i.e. Zn/Sn = 1.16, Cu/(Zn+Sn) = 0.74) precursor. The CZTS absorber layers grown by Zn-rich and Cu-/Sn-poor precursors show a bi-layered structure comprising of a well-crystallized photovoltaic layer and a particulate-like bottom layer with a heavily Sn poor content and ZnS educts. More Zn-rich precursors led to a lower quality CZTS absorber layer with large over-grown ZnS crystallites protruding from the bottom absorber layer into the top film, which directly gave rise to apparent quantum efficiency and a sharply reduced device efficiency. The cell grown by the slightly Sn-rich precursor had the best-developed CZTS absorber with compact and large grains, however, a lower efficiency.

Preparation and properties of ZnO:Mo thin films deposited by RF magnetron sputtering

Mo doped ZnO thin films (ZnO:Mo, MZO) were prepared on quartz glass substrates by RF magnetron sputtering at the lower substrate temperatures (room temperature (RT) and 100°C). Their structural, electrical and optical properties were studied by X-ray diffractometry (XRD), four probe technique, Hall measurement, and UV-VIS-NIR spectrophotometer, respectively. XRD showed that the resultant films were wurtzite structure with c-axis preferential orientation. As the substrate temperatures increasing, the thickness of the film increased and the crystallinity became better. The resistivity of the films were 3.44x10-3 Ω•cm and 3.31x10-3 Ω•cm for the films deposited at RT and 100°C, respectively. The corresponding average transmittance in visible and near IR region (400-1100nm) was 81.7 % and 74.5 %, respectively. In addition, for the film deposited at 100°C, the refractive index (n) and band gap (Eg) were obtained by fitting the transmittance spectra and discussed.

Preparation of CuInSe2 thin films by spin-coating and selenization

In order to fabricate low cost and printable CuInSe2 (CIS) thin film solar cells, a chemical process has been developed to fabricate uniform CIS films with large grain size and close stoichiometry to chalcopyrite phase. Cu(NO3)2, InCl3 and ethyl cellulose (EC) were adopted to form the starting solution. CIS films were prepared by spin-coating and selenization. Precursor films and CIS films were investigated by SEM, EDS and XRD. CuCl and InCl3 crystals appeared in the precursor films. During the selenization process, CuCl first reacted with Se vapor to form Cu2-xSe. With increasing selenization temperature, InCl3 reacted with Cu2-xSe to form CIS accompanying the evaporation of chlorine in the form of gas. It is revealed that the element ratio in final CIS film is determined by the raw material ratio in the starting solution and the selenization temperature.

Effects of post annealing on structural, electrical and optical properties of ZnO:Al thin films prepared by RF magnetron sputtering

Al doped ZnO (ZnO:Al, AZO) thin films were deposited on ordinary soda-lime glass (SLG) substrates by RF magnetron sputtering. Effects of post annealing (300~600 °C for 2~30 min in air and N2, respectively) were studied. All the films were wurtzite structure with highly c-axis preferential orientation. Their electrical properties were relatively stable at the post annealing temperature of 300 °C. As the temperature further increasing, post annealing in air leaded to drastic degradation in the electrical properties, while that in N2 had relatively small influence. Diffusion of alkali ions from SLG substrates was deduced to be one of the influence factors for electrical properties. The spectra measurements showed that the post annealing mainly affected the transmittance in the near-infrared and infrared (NIR-IR) range and the optical band gap (Eg). The variation of Eg was attributed to the Burstein-Moss (BM) shift modulated by many-body effects.