Maobin Wei

Blocking the Formation of Zn2+/Dye Complexes in Dye-Sensitized Solar Cells by Inserting CdS Quantum Dots into Sandwich Layer

ZnO NRAs are grown on ITO substrates by a simple chemical method. CdS QDs were deposited on ZnO NRAs by SILAR. N719 was synthesized by dipping method. J–V analysis indicates that by inserting a layer of CdS QDs, the conversion efficiency of DSSCs was improved obviously. The device with CdS QDs shows the higher conversion efficiency due to the three reasons: (1) CdS QDs enhanced adsorption spectra of DSSCs in the visible region; (2) CdS QDs block the formation of Zn2+/dye complex, it is beneficial for electros transport from dye to ZnO photoanode. It is the key to obtain higher conversion efficiency; (3) FRET dynamics exists by the introduction of CdS QDs.

Synthesis of simple, low cost and benign sol–gel Cu2InxZn1−xSnS4 alloy thin films: influence of different rapid thermal annealing conditions and their photovoltaic solar cells

Cu2InxZn1−xSnS4 (x = 0.4) alloy thin films were synthesized on soda lime glass (SLG) substrate by a simple low-cost sol–gel method followed by a rapid annealing technique. The influence of sulfurization temperature and sulfurization time on the structure, morphology, optical and electrical properties of Cu2InxZn1−xSnS4 thin films was investigated in detail. The XRD and Raman results indicated that the crystalline quality of the Cu2InxZn1−xSnS4 alloy thin films was improved, accompanied by metal deficiency, particularly tin loss with increasing the sulfurization temperature and sulfurization time. From absorption spectra it is found that the band gaps of all Cu2InxZn1−xSnS4 films are smaller than that (1.5 eV) of the pure CZTS film due to In doping, and the band gap of the Cu2InxZn1−xSnS4 films can be tuned in the range of 1.38 to 1.19 eV by adjusting the sulfurization temperature and sulfurization time. Hall measurement results showed that all Cu2InxZn1−xSnS4 alloy thin films showed p-type conductivity characteristics, the hole concentration decreased and the mobility increased with the increase of sulfurization temperature and sulfurization time, which is attributed to the improvement of the crystalline quality and the reduction of grain boundaries. Finally, the Cu2InxZn1−xSnS4 film possessing the best p-type conductivity with a hole concentration of 9.06 × 1016 cm−3 and a mobility of 3.35 cm2 V−1 s−1 was obtained at optimized sulfurization condition of 580 °C for 60 min. The solar cell using Cu2InxZn1−xSnS4 as the absorber obtained at the optimized sulfurization conditions of 580 °C for 60 min demonstrates a power conversion efficiency of 2.89%. We observed an increment in open circuit voltage by 90 mV. This work shows the promising role of In in overcoming the low Voc issue in Cu-kesterite thin film solar cells.

Enhanced Magnetic Properties of BiFeO3 Thin Films by Doping: Analysis of Structure and Morphology

The improvement of ferromagnetic properties is critical for the practical application of multiferroic materials, to be exact, BiFeO3 (BFO). Herein, we have investigated the evolution in the structure and morphology of Ho or/and Mn-doped thin films and the related diversification in ferromagnetic behavior. BFO, Bi0.95Ho0.05FeO3 (BHFO), BiFe0.95Mn0.05O3 (BFMO) and Bi0.95Ho0.05Fe0.95Mn0.05O3 (BHFMO) thin films are synthesized via the conventional sol-gel method. Density, size and phase structure are crucial to optimize the ferromagnetic properties. Specifically, under the applied magnetic field of 10 kOe, BHFO and BFMO thin films can produce obvious magnetic properties during magnetization and, additionally, doping with Ho and Mn (BHFMO) can achieve better magnetic properties. This enhancement is attributed to the lattice distortions caused by the ionic sizes difference between the doping agent and the host, the generation of the new exchange interactions and the inhibition of the antiferromagnetic spiral modulated spin structure. This study provides key insights of understanding the tunable ferromagnetic properties of co-doped BFO.