Lijian Huang

Fabrication of a Cu2ZnSn(S,Se)4 Photovoltaic Device by a Low-Toxicity Ethanol Solution Process

Homogeneous molecular precursor solutions are excellent choices for obtaining smooth absorber layers, and they offer the potential to significantly lower the manufacturing cost of solar cells. Here, we present a thermally degradable metal butyldithiocarbamate-based solution approach to fabricate Cu2ZnSn(S,Se)4 solar cells. Low-cost Cu2O, ZnO, and SnO were used as the starting materials and were dissolved in the ethanol solution of butyldithiocarbamic acid. By tuning the composition of the Cu2ZnSn(S,Se)4 thin film, a power conversion efficiency of 6.03% on the basis of the active area has been achieved.

Solution-Processed Highly Efficient Cu2ZnSnSe4 Thin Film Solar Cells by Dissolution of Elemental Cu, Zn, Sn, and Se Powders

Solution deposition approaches play an important role in reducing the manufacturing cost of Cu2ZnSnSe4 (CZTSe) thin film solar cells. Here, we present a novel precursor-based solution approach to fabricate highly efficient CZTSe solar cells. In this approach, low-cost elemental Cu, Zn, Sn, and Se powders were simultaneously dissolved in the solution of thioglycolic acid and ethanolamine, forming a homogeneous CZTSe precursor solution to deposit CZTSe nanocrystal thin films. Based on high-quality CZTSe absorber layer, pure selenide CZTSe solar cell with a photoelectric conversion efficiency of 8.02% has been achieved without antireflection coating.

Metal sulfide precursor aqueous solutions for fabrication of Cu2ZnSn(S,Se)4 thin film solar cells

Aqueous solution deposition of metal chalcogenide semiconductor thin films is considered a green and low-cost approach. However, it is hard to find a general aqueous solution approach to deposit various kinds of high-quality metal sulfide thin films. Here, we describe a green and robust ammonium thioglycolate aqueous solution approach, and fifteen types of metal sulfide precursor solutions (metal = Cu, Zn, Sn, Ge, In, Sb, Mg, Cd, Mn, Bi, Fe, Ni, Li, Na, K) can be prepared using metal oxides or metal hydroxides as raw materials at room temperature under an air atmosphere. Moreover, elemental sulfur and selenium can also be highly dissolved. By this green route, high quality CZTS nanocrystal thin films can be deposited by directly coating the mixed Cu, Zn, and Sn precursor solutions without the need for complex nanocrystal synthesis. The remarkable power conversion efficiency of 6.62% was achieved, which is the highest value for aqueous solution deposited CZTSSe thin film solar cells.

Fabrication of Cu2ZnSn(S,Se)4 solar cells via an ethanol-based sol-gel route using SnS2 as Sn source.

Cu2ZnSn(S,Se)4 semiconductor is a promising absorber layer material in thin film solar cells due to its own virtues. In this work, high quality Cu2ZnSn(S,Se)4 thin films have been successfully fabricated by an ethanol-based sol-gel approach. Different from those conventional sol-gel approaches, SnS2 was used as the tin source to replace the most commonly used SnCl2 in order to avoid the possible chlorine contamination. In addition, sodium was found to improve the short-circuit current and fill factor rather than the open-circuit voltage due to the decrease of the thickness of small-grained layer. The selenized Cu2ZnSn(S,Se)4 thin films showed large densely packed grains and smooth surface morphology, and a power conversion efficiency of 6.52% has been realized for Cu2ZnSn(S,Se)4 thin film solar cell without antireflective coating.

Large-scale synthesis of water-soluble CuInSe2/ZnS and AgInSe2/ZnS core/shell quantum dots

Water-soluble CuInSe2/ZnS (CISe/ZnS) and AgInSe2/ZnS (AISe/ZnS) core/shell quantum dots (QDs) on a multigram scale have been synthesized by using gelatin and thioglycolic acid as dual stabilizers in an electric pressure cooker. The core/shell QDs present composition-tunable emission in the range of 582 nm to 686 nm with a maximum PLQY of 23.3%. The core/shell QDs also exhibit good water/buffer stability. The red-emitting CISe/ZnS QDs are applied as wavelength converters to achieve warm white light-emitting diodes.

Tuning the Band Gap of Cu2ZnSn(S,Se)4 Thin Films via Lithium Alloying

Alkali metal doping plays a crucial role in fabricating high-performance Cu(In,Ga)(S,Se)2 and Cu2ZnSn(S,Se)4 (CZTSSe) thin film solar cells. In this study, we report the first experimental observation and characterizations of the alloyed Li(x)Cu(2-x)ZnSn(S,Se)4 thin films. It is found that Cu(+) ions in Cu2ZnSn(S,Se)4 thin films can be substituted with Li(+) ions, forming homogeneous Li(x)Cu(2-x)ZnSn(S,Se)4 (0 ≤ x ≤ 0.29) alloyed thin films. Consequently, the band gap, conduction band minimum, and valence band maximum of Li(x)Cu(2-x)ZnSn(S,Se)4 thin films are profoundly affected by Li/Cu ratios. The band alignment at the Li(x)Cu(2-x)ZnSn(S,Se)4/CdS interface can be tuned by changing the Li/Cu ratio. We found that the photovoltaic parameters of the Li(x)Cu(2-x)ZnSn(S,Se)4 solar cell devices are strongly influenced by the Li/Cu ratios. Besides, the lattice constant, carrier concentration, and crystal growth of Li(x)Cu(2-x)ZnSn(S,Se)4 thin films were studied in detail.

Homogeneous Synthesis and Electroluminescence Device of Highly Luminescent CsPbBr3 Perovskite Nanocrystals

Highly luminescent CsPbBr3 perovskite nanocrystals (PNCs) are homogeneously synthesized by mixing toluene solutions of PbBr2 and cesium oleate at room temperature in open air. We found that PbBr2 can be easily dissolved in nonpolar toluene in the presence of tetraoctylammonium bromide, which allows us to homogeneously prepare CsPbBr3 perovskite quantum dots and prevents the use of harmful polar organic solvents, such as N,N-dimethylformamide, dimethyl sulfoxide, and N-methyl-2-pyrrolidone. Additionally, this method can be extended to synthesize highly luminescent CH3NH3PbBr3 perovskite quantum dots. An electroluminescence device with a maximal luminance of 110 cd/m2 has been fabricated by using high-quality CsPbBr3 PNCs as the emitting layer.

New Insight of Li-Doped Cu2ZnSn(S,Se)4 Thin Films: Li-Induced Na Diffusion from Soda Lime Glass by a Cation-Exchange Reaction

In our recent report (ACS Appl. Mater. Interfaces 2016, 8, 5308), Li+ ions had been successfully incorporated into the lattice of the selenized Cu2ZnSn(S,Se)4 thin film on a quartz substrate by substituting equivalent Cu+ ions, and Li+ ions was also found to have the little effect on the crystal growth and defect passivation. To further improve the cell performance of Li-doped CZTSSe devices, we conducted the same experiments on the sodium-rich soda-lime glass (SLG) substrate in this study, instead of sodium-free quartz substrate. Surprisingly, only trace amounts of Li (Li/Cu molar ratio ∼1 × 10-4) were detected in the final CZTSSe thin films; meanwhile, a large amount of sodium was present on the surface and at the grain boundaries of the selenized thin films. A Li/Na exchange mechanism is used to explain this phenomenon. Only on the sodium-free substrate can Li+ ions enter the CZTSSe host lattice, and doping Li+ ions on the SLG substrate are nearly identical to doping Na+ ions.