Yufang Li

A 4.92% efficiency Cu2ZnSnS4 solar cell from nanoparticle ink and molecular solution

Quaternary Cu2ZnSnS4 (CZTS) thin films were prepared by a low-cost, simple and environmentally-friendly ink method. By depositing molecular solution on the nanoparticle thin film, the quality of as-prepared CZTS thin films was greatly improved (e.g. reduction of fine grain layer formation and improved crystallinity). The effect of the number of spin-coated layers from molecular solution on solar cell performance was investigated. The results indicated that the CZTS thin film had the best performance when 5 layers were spin-coated from molecular solution on the nanoparticle thin film. The crystallinity of the as-prepared CZTS thin film and the interface at Mo/CZTS was found to be obviously enhanced by addition of a molecular solution layer. Finally, a CZTS thin film solar cell with an efficiency of 4.92% has been fabricated.

Growth mechanism of Ge-doped CZTSSe thin film by sputtering method and solar cells

Ge-doped CZTSSe thin films were obtained by covering a thin Ge layer on CZTS precursors, followed by a selenization process. The effect of the Ge layer thickness on the morphologies and structural properties of Ge-doped CZTSSe thin films were studied. It was found that Ge doping could promote grain growth to form a compact thin film. The lattice shrank in the top-half of the film due to the smaller atomic radius of Ge, leading to the formation of tensile stress. According to thermodynamic analysis, Sn was easier to be selenized than Ge. Thus, Ge preferred to remain on the surface and increased the surface roughness when the Ge layer was thin. CZTSe was easier to form than Ge-doped CZTSe, which caused difficulty in Ge doping. These results offered a theoretical and experimental guide for preparing Ge-doped CZTSSe thin films for the potential applications in low-cost solar cells. With a 10 nm Ge layer on the top of the precursor, the conversion efficiency of the solar cell improved to 5.38% with an open-circuit voltage of 403 mV, a short-circuit current density of 28.51 mA cm-2 and a fill factor of 46.83% after Ge doping.

High-Efficient Solar Cells by the Ag/Cu-Assisted Chemical Etching Process on Diamond-Wire-Sawn Multicrystalline Silicon

In this paper, we presented a novel low-cost method for diamond-wire-sawn (DWS) multicrystalline silicon (mc-Si) wafer texturation based on the metal-assisted chemical etching process with Ag/Cu dual elements and nanostructure rebuilding (NSR) treatment to remove the saw marks and to realize uniform invert pyramid textured structures. Benefiting from both the increased optical absorption and better passivation, an efficiency of 18.71% for invert pyramid mc-Si solar cells from a DWS wafer with a standard size of 156 × 156 mm2 was obtained, which was 0.58% and 2.33% absolutely higher than that (18.13%) of the traditional mc-Si solar cell and than that (16.38%) of the black mc-Si solar cell without NSR treatment, respectively.

Efficient light trapping of quasi-inverted nanopyramids in ultrathin c-Si through a cost-effective wet chemical method

In this paper, we report quasi-inverted nanopyramids (QIP) for light-trapping in ultrathin c-Si by a cost-effective wet chemical method. The QIP is fabricated by a well-known two-step Ag assisted chemical etching method followed by a post nanostructure rebuilding (NSR) process, lowering the surface area to ∼3.0 times for suppressing surface recombination losses. The comparable average absorptance value of 43 μm c-Si with double-sided QIP to that of 182 μm c-Si with double-sided conventional pyramid in the spectral range of 300–1100 nm demonstrates an over 4.2-fold reduction in material usage. Finally, a simulation model is proposed to explain the superiority of our QIP compared with the periodic inverted pyramid (IP) structure of the same size, presenting a promising method to the mass production of high-efficiency ultrathin c-Si HIT solar cells.

Large resonance magnetoelectric response in Ni(Terfenol-d)/Pb(Zr,Ti)O3 bilayer laminate composites

In this work we report magnetoelectric laminate composites made up of negative magnetostrictive Ni plates, positive magnetostrictive Tb0.3Dy0.7Fe2 (Terfenol-d) plates and piezoelectric Pb(Zr,Ti)O3 (PZT) plates, in which negative and positive magnetostrictive plates are bonded on the piezoelectric plate and conjugate longitudinally with various orders. Both Ni-Terfenol-d-Ni/PZT and Terfenol-d-Ni-Terfenol-d/PZT composites are constructed and compared with Ni/PZT and Terfenol-d/PZT composites. The bias magnetic field and the frequency dependences of the magnetoelectric coefficient suggest that Ni-Terfenol-d-Ni/PZT is an optimal configuration with excellent magnetoelectric effects such as a large magnetoelectric coefficient at a low bias magnetic field and a low resonance frequency at which the maximum ME voltage coefficient appears. Besides, compared with most of other bulk composites configuration with Terfenol-d plates, the Ni-Terfenol-d-Ni/PZT composite reduces the Terfenol-d usage. We believe that the Ni-Terfenol-d-Ni/PZT composite is useful for the application due to its simple configuration and large resonance magnetoelectric response at a low frequency.

Impact of thiourea concentration on the properties of sol–gel derived Zn(O,S) thin films and Cu(In,Ga)Se 2 solar cells

AbstractA novel approach based on sol–gel spin coating method to deposit Zn(O,S) thin film using thiourea(TU) as a sulfur source replacing CdS as buffer layer was developed and the influence of TU concentration on the properties of Zn(O,S) thin films and Cu(In,Ga)Se2(CIGS) solar cells were investigated in this paper. It was found by X-ray diffraction and X-ray photoelectron spectroscopy that sol–gel derived Zn(O,S) thin films were amorphous and composed of ZnS, ZnO as well as Zn(OH)2. The variation of the optical band gap as a function of the S/(S+O) ratio was determined by energy-dispersive spectroscopy and UV-VIS-NIR. The results indicated that the minimum value for band gap of approximate 3.72 eV was obtained when the S/(S+O) = 0.44. Efficiency of up to 7.28% was achieved for a CIGS solar cell with Zn(O,S) buffer layer from 0.2M TU, which was attributed to the optimized conduction band offset (CBO) of +0.45 eV at the CIGS/Zn(O,S) interface. Zn(O,S) thin films prepared in sol–gel route was used to replace traditional CdS buffer layer deposited by chemical bath deposition method in Cu(In,Ga)Se2 solar cells. The best efficiency was achieved for CIGS/Zn(O,S)/i-ZnO/ITO heterostructure solar cell with S/(S+O) = 0.18, which was attributed to the optimized conduction band offset (CBO) of +0.45 eV at the CIGS/Zn(O,S) interface.

Effect of e-beam evaporated elemental metal stack precursors on the property of Cu(InGa)Se2 thin films through two-step process

Two-step process is considered to be more simple than co-evaporation method in Cu(InGa)Se2 (CIGS) thin films preparation process. However, research on CIGS thin films prepared by two-step process based on evaporation of elemental metals Cu, In and Ga is hardly reported. In this work, four types of metal stacks engineered as In/Ga/Cu/Ga/In (type A), Cu/Ga/In (type B), Cu/In/Ga (type C) and Cu/Ga/In/Cu (type D) were prepared and effects of metal stack precursors on properties of CIGS thin films formed by two-step process were studied. All types of precursors consisted of Cu–In, Cu–Ga and In phases. CIGS thin film from type A precursor showed poor compactness and relative high surface roughness due to the ordered defect compounds on the surface. Type B precursor exhibited a better compactness and crystal quality which led to an optimal structural property of films among all types of CIGS thin films. The reduction of Ga/(Ga + In) and the gaps appeared at the Mo/CIGS interface of CIGS thin film from type C precursor were explained by the re-evaporation of Ga element and compensation of In element during selenization. Grain size in CIGS thin film from type D is a little smaller than that from type B. Models of selenization process in different types of precursors were given. CIGS solar cell from type B exhibited the highest conversion efficiency of 9.2%.

Multiple modulations of strain- and charge-mediated converse magnetoelectric coupling effects in a STO/Fe3O4/Au/PZT multiferroic heterostructure

The multiple modulations of strain- and charge-mediated converse magnetoelectric coupling effects have been achieved in a multiferroic heterostructure of SrTiO3(STO)/Fe3O4/Au/PbZr0.52Ti0.48O3(PZT) multilayers grown on a Nb:SrTiO3 substrate. By altering the position of the applied electric field, the heterostructure is divided into three structure parts, i.e., Fe3O4/Au/PZT, STO/Fe3O4, and STO/Fe3O4/Au/PZT. In such an optimized heterostructure, the strain and charge effects can be directly separated, quantified, and co-regulated and the pure strain, pure charge, and the combined strain and charge effects can thus be obtained, respectively. The in-plane magnetization variation behaviors induced by electric fields are different for the three individual modulations, which are closely related to the interfacial strain propagation and interfacial charge accumulation. It is also found that the strain and charge effects can interact with each other as the two interfacial effects coexist.The multiple modulations of strain- and charge-mediated converse magnetoelectric coupling effects have been achieved in a multiferroic heterostructure of SrTiO3(STO)/Fe3O4/Au/PbZr0.52Ti0.48O3(PZT) multilayers grown on a Nb:SrTiO3 substrate. By altering the position of the applied electric field, the heterostructure is divided into three structure parts, i.e., Fe3O4/Au/PZT, STO/Fe3O4, and STO/Fe3O4/Au/PZT. In such an optimized heterostructure, the strain and charge effects can be directly separated, quantified, and co-regulated and the pure strain, pure charge, and the combined strain and charge effects can thus be obtained, respectively. The in-plane magnetization variation behaviors induced by electric fields are different for the three individual modulations, which are closely related to the interfacial strain propagation and interfacial charge accumulation. It is also found that the strain and charge effects can interact with each other as the two interfacial effects coexist.