Fanxu Meng

Role of tungsten oxide in inverted polymer solar cells

Tungsten oxide (WO3) was inserted as an anode interfacial layer between the photoactive layer and top electrode in inverted polymer solar cells (PSCs) with nanocrystalline titanium dioxide as an electron selective layer. The device with WO3 exhibited a remarkable improvement in power conversion efficiency compared with that without WO3, which indicated that WO3 efficiently prevented the recombination of charge carriers at the organic/top electrode interface. The dependence of the device performances on WO3 film thickness and different top metal electrodes was investigated. Transparent inverted PSCs with thermally evaporable Ag/WO3 as a transparent anode were also investigated when introducing a WO3 buffer layer.

Semitransparent inverted polymer solar cells with MoO3/Ag/MoO3 as transparent electrode

Semitransparent inverted polymer solar cells were developed using thermally evaporable MoO3/Ag/MoO3 as transparent anode. The ultrathin inner MoO3 layer was introduced as a buffer layer to improve hole collection, while the outer MoO3 layer served as a light coupling layer to enhance optical transmittance of the device. The dependence of the device performances on the thickness of the outer MoO3 layer was investigated. The results showed that the addition of the outer MoO3 layer improves the transmittance of the anode compared to MoO3/Ag anode and the performances of the semitransparent devices with the outer MoO3 layer are improved due to the reduced series resistance.

Semitransparent polymer solar cells with one-dimensional (WO3/LiF)N photonic crystals

One-dimensional (WO3/LiF)N photonic crystals (1DPCs) are deposited on the Ag cathode of the semitransparent polymer solar cells to improve the efficiency of the device. The 1DPCs with 8 pair of WO3/LiF act as distributed reflectors within the photonic bandgap. Then, power conversion efficiency of 2.58% is achieved and there is an improvement of 26.3% in the efficiency when compared with that of the conventional device without the 1DPCs. The average transmittance of the device with 8 pair of WO3/LiF is almost zero in 400–600 nm wavelength range. It means that the light is absorbed sufficiently in the active layer. The enhanced light absorption results in efficiency improvement remarkably.

The role of Ag nanoparticles in inverted polymer solar cells: Surface plasmon resonance and backscattering centers

Here, we demonstrate silver (Ag) nanoparticles (NPs) existing in molybdenum trioxide (MoO3) buffer layers can improve the photocurrent by surface plasmon resonance (SPR) and backscattering enhancement. The device structure is glass/indium tin oxides/titanium dioxide (TiO2)/regioregular poly(3-hexylthiophene):[6,6]-phenyl C61 butyric acid methyl ester/MoO3/Ag NPs/MoO3/Ag. Compared to the device without Ag NPs, the short current density (Jsc) is improved from 7.76 ± 0.14 mA/cm2 to 8.89 ± 0.12 mA/cm2, and the power conversion efficiency is also enhanced from 2.70% ± 0.11% to 3.35% ± 0.08%. The transmittance spectra show that the device with Ag NPs has weaker transmittance than the device without, which could be attributed to the photons absorption of Ag NPs and light scattering by Ag NPs. The absorption profile of the devices with or without Ag NPs is simulated using finite-difference time-domain methods. It is approved that the Ag NPs result in the absorption improvement by SPR and backscattering enhancement.

Performance improvement of inverted polymer solar cells by doping Au nanoparticles into TiO2 cathode buffer layer

Gold nanoparticles (Au NPs) were synthesized by a facile method. Then Au NPs with different sizes and weight ratios were blended into the TiO2 cathode buffer layer of the polymer solar cells (PSCs) with a blend of poly (3-hexylthiophene) (P3HT) and [6,6]-phenyl-C61-butyric acid methyl ester (PCBM) as the active layer. The light absorption of the devices was enhanced by incorporating Au NPs into the Bulk heterojunction (BHJ) polymer solar cells, which support localized surface plasmon resonance (LSPR). The results showed that the short-circuit current density (JSC) was apparently enhanced by doping Au NPs into the buffer layer while maintaining the open-circuit voltage (VOC) and fill factor(FF), leading to an increase in power conversion efficiency.

Open-circuit voltage enhancement of inverted polymer bulk heterojunction solar cells by doping NaYF4 nanoparticles/PVP composites

NaYF4 nanoparticles (NPs) were synthesized by a facile solvothermal approach using polyvinylpyrrolidone (PVP) as a surfactant. The NPs were doped into P3HT:PCBM blend to fabricate inverted polymer bulk heterojunction (BHJ) solar cells. The dependence of device performance on the weight ratio of NPs in the blend film was investigated. The results showed that the open-circuit voltage was apparently enhanced by doping NaYF4 NPs/PVP composites into the active layer while maintaining the short-circuit current density and fill factor, leading to an increase in power conversion efficiency. The results of cyclic voltammetry measurement revealed that PVP had a deeper HOMO energy level than that of P3HT. PVP carried by NPs might also form charge transfer (CT) complexes with PCBM, which can make contributions to the open-circuit voltage. The study of photoluminescence (PL) spectra indicated clear evidence for enhanced exciton dissociation and reduced charge recombination in the blend film with NPs.

Influences of surface capping with electrostatically self-assembled PEI on the photoresponse of a TiO2 thin film

The photoresponse of a TiO2 thin film was significantly improved due to the decrease in the Schottky barrier height between Au and TiO2 via the formation of interface dipoles, which was caused by electrostatically self-assembled PEI on the surface of the TiO2 film.

Synthesis and highly enhanced acetylene sensing properties of Au nanoparticle-decorated hexagonal ZnO nanorings

Hexagonal ZnO nanorings were synthesized using a one-step hydrothermal method and Au nanoparticles were decorated on the surface of the ZnO nanorings through a facile deposition process. The as-prepared ZnO nanorings showed a well-defined hexagonal shape with a width of 0.75–1.4 μm, a thickness of 0.17–0.33 μm and a hollow size of 0.2–1 μm. For the Au nanoparticle-decorated hexagonal ZnO nanorings (Au–ZnO nanorings), Au nanoparticles with a size of 3–10 nm were distributed discretely on the surface of the ZnO nanorings. The acetylene sensing performance was tested for the ZnO nanorings and Au–ZnO nanorings. The results indicated that the Au–ZnO nanorings showed a higher response (28 to 100 ppm acetylene), lower operating temperature (255 °C), faster response/recovery speed (less than 9 s and 5 s, respectively), and lower minimum detectable acetylene concentration (about 1 ppm). In addition, the mechanism for the enhanced acetylene-sensing performance of the Au–ZnO nanorings was discussed.

Performance Improvement of Low-Band-Gap Polymer Solar Cells by Optical Microcavity Effect

We investigate the performance of the indium tin oxide (ITO)-free low-band-gap polymer solar cells (PSCs) with a WO3/Ag/WO3 multilayer as a transparent electrode. For the device with a 60-nm-thick active layer, the efficiency is improved by 26.5% when compared with that of the device with an ITO electrode. The improvement can be attributed to the resonance effect of the microcavity structure occurring between the transparent WO3 /Ag/WO3 and top metal electrode. Further investigation based on the incident photon-to-electron conversion efficiency spectra test and transfer matrix simulation is performed to expatiate on the effects of the microcavity on the performance of the low-band-gap PSCs with the WO3/Ag/WO3 multilayer as the transparent electrode.

The Role of Fe3O4 Nanocrystal Film in Bilayer-Heterojunction CuPc/C-60 Solar Cells

The CuPc/C60 thin-film bilayer-heterojunction solar cells are fabricated by vacuum deposition with bathocuproine (BCP) as the exciton-blocking layer. Ferroferric oxide (Fe3O4) nanocrystal film is inserted between the copper phthalocaynine (CuPc) layer and indium tin oxide (ITO) anode. The device performances dependent on the thickness of Fe3O4 are investigated and compared. The results show that both the short-circuit current density and fill factor are enhanced by introducing a 1 nm Fe3O4 buffer layer, leading to an increase of power conversion efficiency. The role of Fe3O4 as a buffer layer in the improvement of the device performances is studied in detail by ultraviolet photoemission spectroscopy (UPS).