P3HT:PCBM, best seller in polymer photovoltaic research

In the field of polymer‐based photovoltaic cells, poly(3‐hexylthiophene) (P3HT) and 1‐(3‐methoxycarbonyl)propyl‐1‐phenyl[6,6]C₆₁ (PCBM) are, to date, the most‐studied active materials around the world for the bulk‐heterojunction structure. Various power‐conversion efficiencies are reported up to approximately 5%. This Research News article is focused on a survey of the tremendous literature published between 2002 and 2010 that exhibits solar cells based on blends of P3HT and PCBM.     

Charge transfer in blends of P3HT and colloidally prepared CuInS2 nanocrystals

CuInS₂ (CIS) is a suitable semiconductor for thin film photovoltaics and also a promising candidate to replace CdSe in hybrid polymer/nanoparticle solar cells, advantages being the lower toxicity and the better absorption properties. In this work, crystalline nanoparticles of CuInS₂ were successfully synthesized with uniform size and shape by means of colloidal chemistry. Photo-induced absorption spectroscopy was used to study charge transfer between poly(3-hexylthiophene) (P3HT) and the CIS nanoparticles. The appearance of signals corresponding to positive polarons provides evidence that charge transfer is possible in the P3HT/CIS system.     

PS-b-P3HT copolymers as P3HT/PCBM interfacial compatibilizers for high efficiency photovoltaics

A conducting diblock copolymer of PS-b-P3HT was added to serve as a compatibilizer in a P3HT/PCBM blend, which improved the power-conversion efficiency from 3.3% to 4.1% due to the enhanced crystallinity, morphology, interface interaction, and depth profile of PCBM.     

Investigation of P3HT/n-Si heterojunction using surface photovoltage spectroscopy

Surface photovoltage spectroscopy (SPS) was used to investigate the interactions of the interface between regioregular poly(3-hexylthiophene) (P3HT) and n-type single crystalline silicon. The SPS responses of silicon and the P3HT/n-Si heterojunction caused by band to band transition of silicon are 30 mV and 160 mV respectively. The band-bending in the silicon side of the P3HT/n-Si structure is larger than that of bare n-Si. The density of the interface states of the P3HT/n-Si heterojunction increased significantly after the deposition of P3HT. Based on the contact potential difference (CPD) transient results, charge transport and separation processes are fast in the silicon substrate and slow in the P3HT layer respectively.     

基于P3HT的有机太阳能电池的特性研究

聚3已基噻吩（P3HT）是近年来出现的一种新型有机聚合物太阳能电池的供电子体材料。通过真空蒸镀与旋涂相结合的方法,制备了基于聚合物P3HT的结构为ITO/Buffer layer/P3HT/C60/Bphen/Ag的有机太阳能电池。测试结果表明P3HT、C60的优化厚度分别为30、40nm。如果还引入金属氧化物MoO3作为阳极缓冲层,能够明显地提高电池的开路电压,其中MoO3阳极缓冲层的优化厚度为1nm。因此,通过优化制备工艺、引入新的器件材料,能更理想地调控太阳能电池的性能参数。     

Solution-processed,flexible and broadband photodetector based on CsPbBr_3/PbSe quantum dot heterostructures

Due to their promising applications in foldable displays,optical communication equipment and environmental monitoring systems,flexible and broadband optoelectronic devices have gained extensive attention in recent years.Here,a flexible and broadband photodetector based on CsPbBr₃/PbSe quantum dot(QD) heterostructures is firstly presented.The integrated QD heterostructures possess consecutive detection range from ultraviolet(UV) to long-wave length infrared(LW-IR) regions with efficient light absorption and chemical stability,in comparison with the pristine PbSe QDs.Systematic material characterizations reveal the improved exciton dissociation,carrier transport and carrier lifetime of the QD heterostructures.Flexible photodetector Ag/CsPbBr₃/PbSe/Ag demonstrate a high responsivity of 7.17 A/W with a specific detectivity of 8.97 × 10¹² Jones under 25 μW/cm² 365 nm illumination at 5 V.Furthermore,it could maintain 91.2 %(or 94.9 %) of its initial performance even after bending for thousands of times(or exposing in ambient air for 4 weeks).More importantly,its re s ponse time is shortened more than three orders of magnitude as that of pristine PbSe QDs-based photodetectors.Therefore,it provides a feasible and promising method for the next-generation high-performance broadband photodetectors via constructing heterostructures of various QDs.     

Thermal annealing effect on the nanomechanical properties and structure of P3HT:PCBM thin films

Nanostructured polymer-fullerene thin films are among the most prominent materials for application in high efficient polymer solar cells. Specifically, poly(3-hexylthiophene) (P3HT) and fullerene derivatives (PCBM) blends are used as the donor/acceptor materials forming a bulk heterojunction. Although P3HT:PCBM properties have been extensively studied, less light has been set on its nanomechanical properties, which affect the device service life. In this work Atomic Force Acoustic Microscopy (AFAM), Atomic Force Spectroscopy and Nanoindentation were used to study the effect of the fullerene presence and the annealing on the P3HT:PCBM nanomechanical behavior. The P3HT:PCBM thin films were prepared by spin coating on glass substrates and then annealed at 100 °C and 145 °C for 30 min. Large phase separation was identified by optical and Atomic Force Microscopy (AFM) for the annealed samples. Needle-like PCBM crystals were formed and an increase of the polymer crystallinity degree with the increase of the annealing temperature was confirmed by X-ray diffraction. AFAM characterization revealed the presence of aggregates close to stiff PCBM crystals, possibly consisting of amorphous P3HT material. AFM force-distance curves showed a continuous change in stiffness in the vicinity of the PCBM crystals, due to the PCBM depletion near its crystals, and the AFM indentation provided qualitative results about the changes in P3HT nanomechanical response after annealing.     

Influence of P3HT concentration on morphological, optical and electrical properties of P3HT/PS and P3HT/PMMA binary blends

Poly(3-hexylthiophene) (P3HT) has interesting optoelectronic properties and a wide variety of applications such as solar cells and O-FET devices. It is a soluble conductive polymer but their mechanical properties are poor and its conductivity is unstable in environmental condition. With the finality of overcome these disadvantages, P3HT binary blends with two insulating polymers, polystyrene (PS) and polymethylmetacrilate (PMMA), have been synthesized by direct oxidation of 3-hexylthiophene with FeCl₃ as oxidant inside the insulator polymers. Molecular weight and polydispersity of P3HT polymer were measured by size exclusion chromatography and the degree of regioregularity by ¹H RMN. P3HT/PS and P3HT/PMMA thin films were prepared by spin-coating technique from toluene solution at different P3HT concentrations. The doped films were obtained by immersion during 30 s in a 0.3 M ferric chloride (FeCl₃) solution in nitromethane. A classical percolation phenomenon was observed in the electrical properties of the binary blends, it was smaller than 4 wt.% of P3HT in the blend. Atomic force microscopy and confocal microscopy showed a phase-separated morphology. Variation in the surface morphology of the blends was observed, which was a function of the polymer concentration and the type of insulator polymer used in the blends. The insulator polymer was segregated on the surface of the films and showed pit and island-like topography. The pit and island size changed as a function of the polymer concentration. Optical absorption properties as a function of the P3HT concentration in the undoped and doped state were analyzed. In doped state, the bipolaron bands in the PS/P3HT and PMMA/P3HT blends were observed from a P3HT concentration of 1 wt.% and 3 wt.%, respectively. Finally, the polymers were analyzed by thermogravimetric analysis and infrared spectroscopy.     

Effect of post-growth rapid thermal annealing on bilayer InAs/GaAs quantum dot heterostructure grown with very thin spacer thickness

We have investigated the effect of post-growth rapid thermal annealing on self-assembled InAs/GaAs bilayer quantum dot samples having very thin barrier thickness (7.5-8.5 nm). In/Ga interdiffusion in the samples due to annealing is presumed to be controlled by the vertical strain coupling from the seed dots in bilayer heterostructure. Strain coupling from embedded seed QD layer maintains a strain relaxed state in active top islands of the bilayer quantum dot sample grown with comparatively thick spacer layer (8.5 nm). This results in minimum In/Ga interdiffusion. However controlled interdiffusion across the interface between dots and GaAs barrier, noticeably enhances the emission efficiency in such bilayer quantum dot heterostructure on annealing up to 700 °C.     

The role of the annealing temperature on the optical and structural properties of Eu doped GaN/AlN QD

Self assembled molecular beam epitaxy grown GaN quantum dots stacked with AlN spacers were implanted with Eu ions. The as-implanted samples were further submitted to thermal annealing treatments in nitrogen, between 1000 °C and 1200 °C. Eu³⁺ luminescence was observed in all samples with the most intense emission assigned to the ⁵D₀ → ⁷F₂ transition in the red spectral region. The preferential excitation paths of Eu³⁺ luminescence is explored using photoluminescence excitation measurements which allow us to identify the feeding mechanisms for the Eu³⁺ ions inside the GaN quantum dots and AlN host. Optically active Eu centres in both GaN QD and AlN layers could be identified. For low implantation fluence the Eu centres inside GaN QD are dominant while for high fluences the emission arises from Eu in the AlN layers. The annealing temperature, on the other hand, does not cause any change in the local environment of the Eu-ions.     

四氧化三钴/石墨复合改性阳极对海底沉积物微生物燃料电池电化学性能的影响

首次将四氧化三钴/石墨(Co_3O_4/G)复合材料用于海底沉积物微生物燃料电池(MSMFCs)阳极改性,并对阳极电化学性能和电池性能进行研究。结果表明,Co3O4/G复合改性阳极表面的微生物附着数量是空白组的6.1倍;其氧化还原电化学活性和电容特性分别是空白组的16.2倍和31.0倍;交换电流密度达到1.366×10-3m A·cm-2,电子转移动力学活性是空白组的215.6倍,且其抗极化能力最强;电荷转移电阻降至空白组的2/5,并且双电层电容和生物膜电容均得到增加;其组成电池的功率密度为735.1 m W/m2,是空白组电池的4.6倍。机理分析表明,Co_3O_4和石墨的协同作用使复合改性阳极的电容性能和电子转移速率得到提高。     

A study on thermal emission of charges at Si3N4—GaAs interfaces after annealing in N2 and N2 + H2 mixtures

Si₃N₄—GaAs interfaces subjected to annealing in N₂ + H₂ mixture or pure N₂ atmosphere were investigated by a small-signal charge deep-level transient spectroscopy (Q-DLTS) method. The method measures the physical parameters of selective populations of the interface traps continuum. A dependence of the capture cross-section on activation energy was constructed for the continuum of interface states at the Si₃N₄—GaAs interface. The dependence shows an exponential character in the part of the gap ranging from 0.3 to 1.0 eV below the conduction band minimum. It was found that annealing in the temperature interval 400–450 °C reduces the zero-bias band bending by about 0.1 eV. At temperatures of 500 °C and more, degradation of the interface started; compared with annealing in pure N₂ ambient, annealing in an N₂ + H₂ mixture degraded the interface slightly more.     

核-壳结构界面对纳米Ag掺杂BaTiO3@PDA/P(VDF-HFP)复合膜介电和储能性能影响

为改善聚偏氟乙烯（PVDF）基复合材料界面相容性,提高其电性能,利用聚多巴胺（PDA）成功包覆了纳米钛酸钡（BaTiO₃）,并引入纳米Ag离子制备出具有核-壳结构的Ag镶嵌BaTiO₃@PDA-Ag颗粒。以介电聚合物聚偏氟乙烯-六氟丙烯（P（VDF-HFP））为基体,采用溶液流延法制备了BaTiO₃@PDA-Ag/P（VDF-HFP）复合材料厚膜。利用FTIR和XPS验证了BaTiO₃@PDA-Ag/P（VDF-HFP）复合材料结构和形貌,并用宽频介电频谱仪和铁电测试仪分别比较了PDA包覆前后的不同BaTiO₃含量的BaTiO₃@PDA-Ag/P（VDF-HFP）复合膜在低电场下的介电性能和高电场下的电极化性能。结果表明,BaTiO₃@PDA-Ag质量分数为20wt%的BaTiO₃@PDA-Ag/P（VDF-HFP）复合膜在10 Hz下介电常数（ε_r）达到了25,介电损耗（tanδ）仅为0.1,在175 M·Vm-1电场下电极化强度（D_m）为6.2 μC·cm-2,200 M·Vm-1时储能密度（U_e）达到了6.9 J·cm-3,高于其它界面未处理复合膜。以上结果可为此类介电复合材料界面结构处理和电性能研究提供参考。      

Effect of process parameters and post deposition annealing on the optical, structural and microwave dielectric properties of RF magnetron sputtered (Ba0.5,Sr0.5)TiO3 thin films

Thin films of (Ba_0.5,Sr_0.5)TiO₃ (BST5) in the thickness range 400-800 nm have been deposited by RF magnetron sputtering on to quartz substrates at ambient temperature. All the properties investigated, i.e. structure, microstructure, optical and microwave dielectric, show a critical dependence on the processing and post processing parameters. The surface morphology as studied by atomic force microscopy reveals ultra fine grains in the case of as deposited films and coarse grain morphology on annealing. The as-deposited films are X-ray amorphous and exhibit refractive index in the range 1.9-2.04 with an optical absorption edge value between 3.8 and 4.2 eV and a maximum dielectric constant of 35 at 12 GHz. The dispersion in refractive index fits into the single effective oscillator model while the variation in the optical parameters with oxygen percentage in the sputtering gas can be explained on the basis of packing fraction changes. On annealing the films at 900 °C they crystallize in to the perovskite structure accompanied by a decrease in optical band gap, increase in refractive index and increase in the microwave dielectric constant. At 12 GHz the highest dielectric constant achieved in the annealed films is 175. It is demonstrated that with increasing oxygen-mixing percentage in the sputtering gas, the microwave dielectric loss decreases while the dielectric constant increases.     

Effect of substituting Al2O3 and ZrO2 on thermal and optical properties of high refractive index La2O3–TiO2 glass system prepared by containerless processing

La₄Ti₉O₂₄ glass and La₂O₃–TiO₂–Al₂O₃ and La₂O₃–TiO₂–ZrO₂ glass systems were prepared by containerless processing. The thermal stability and refractive indices of these glasses were investigated. It was found that these glasses had high refractive indices over 2.29 and high glass transition temperatures. The effects of substituting Al₂O₃ or ZrO₂ for La₂O₃ or TiO₂ in La₄Ti₉O₂₄ glass on the refractive index is discussed by analyzing the optical parameters of the glasses. The high refractive index of these glasses was due to their large oxygen packing densities and significant electronic polarizabilities of oxygen ions. The substitution of Al₂O₃ and ZrO₂ was effective for the refractive indices and wavelength dispersions.