Materials Science Forum Vols. 663-665

Abstract: Nonlinear optical (NLO) polyimide and a series of polyimide/silica nanohybrids were synthesized from 3,3',4,4'-biphenyltetracarboxylic dianhydride (BPDA), NLO molecule 4-(4’- nitrophenyl-2-yl) phenyl-1,3-diamine, coupling agent and TEOS via sol-gel method. The TEOS content in the hybrids was varied from 0 to 22.5 wt%. The prepared hybrids were characterized by FT-IR, Differential Scanning Calorimetry (DSC), Thermogravimetric Analysis (TGA), Scanning Electron Microscopy (SEM) and Transmission Electron Microscope (TEM). The glass transition temperature (Tg) and the decomposition temperature (Td) at 5 % mass loss were in the range 232~365 °C and 335~475 °C, respectively. The results showed that the prepared materials had excellent thermal stabilities. The electro-optic coefficients (γ33) at 832 nm were in the range of 19-34 pm/V and the values remained well. The experimental results indicate that the prepared thin films have good candidate for electro-optical applications.

Abstract: We have investigated the photoluminescence (PL) of a porous silicon film in which a typical nematic liquid crystal 4-pentyl-4’-cyanobiphenyl infiltrated. Before the liquid crystal filtration, the PL spectrum of the porous silicon film is comprised of two luminescent bands, one of which is located at about 600 nm whereas the other of which is located at about 450 nm. After the liquid crystal filtration, the porous silicon film gives off intense deep-blue PL with its peak located at about 400 nm at the cost of the complete quenching of the PL from the original porous silicon film. Our results have demonstrated that the luminescent properties of porous silicon films can be dramatically modified by liquid crystal infiltration.

Abstract: In this study, microwave annealing treatment was introduced into poly(3-hexylthiophene) (P3HT):[6,6]-phenyl-C61butyric acid methyl ester (PCBM) and poly(9,9‘-dioctylfluorene-cobithiophene (PFT2):PCBM systems instead of thermal annealing treatment. In both systems, microwave annealing showed photovoltaic performane comparable to that of conventional thermal annealing. Through the UV-vis absorption, atomic force microscopy (AFM) and X-ray diffraction (XRD) studies, we were able to confirm that the microwave annealing increases the crystallization of the P3HT polymer chains.

Abstract: Bulk heterojunction organic solar cells made of blended of the electron donor (D) and electron acceptor (A) molecules were fabricated using inkjet printing technique with three different D:A ratios i.e. 1:3, 1:1 and 3:1 (weight). Poly (3-octylthiophene-2,5-diyl) (P3OT) and (6,6)-phenyl C71 butyric acid methyl ester (PC71BM) were used as donor and acceptor respectively. The generated photocurrents and the power conversion efficiency depend on the donor: acceptor ratio, where the device D:A ratio 3:1 generated higher photocurrent. The photovoltaic performance of the devices may also affected by the microstructure and surface morphology of the active layer film.

Abstract: We report here a series of polypyrrole/C60-H3PO4 two-layer photovoltaic cells fabricated by varying the C60 ratio with regard to polypyrrole. It is found that a slight amount of C60 can remarkably improve photovoltaic properties by four orders of magnitude; with C60 ratio the open-circuit voltage and short-circuit current increase, and at higher C60 ratio the photovoltaic working threshold is lowered too, the cell can even work efficiently in dark, more approaching the efficiency under strong illumination. The optimized device yields 1.2 V open-circuit voltage and 14 μA/cm2 short-circuit current, and a power conversion efficiency 0.01%. Our results show that polypyrrole is a potentially good material for photovoltaic cells. The effect of C60 in combination with polypyrrole is discussed.

Abstract: For the purpose of developing novel photovoltaic materials and organic photovoltaic devices with good performance characteristics, 5-cyano-2,2′:5′,2″-terthiophene (3T-CN) and 5-cyano -2,2′:5′,2″:5″,2″′-tetrathiophene (4T-CN) were synthesized. The 3T-CN and 4T-CN was donor-acceeptor type oligothiophene derivatives with liquid crystal properties. The rigid and flexible photovoltaic devices were fabricated using 3T-CN, 4T-CN and 3,4,9,10-perylenetertracarboxylic dianhydride (PTCDA). Comparision of the rigid device based on 4T showed that both rigid device glass-ITO/4T-CN/PTCDA/Al and flexible device PET-ITO/4T-CN/PTCDA/Al had higher short circuit current density (Isc) and power conversion efficiency (PCE) than that of glass-ITO/4T /PTCDA/Al. The -CN group played an important role in increasing Isc and PCE. It is due to that the mesogenic properties of 4T-CN, which enhances the efficiency by promoting forward interfacial electron transfer.

Abstract: The primary aim of this communication is to introduce a novel approach of preparation of solar cell, viz. PS based solar cell, which is on the basis of the basic principle of the well established photovoltaic effect. We carefully investigate the current-voltage characteristics of the PS-based solar cell by virtue of performing the measurement of both current and voltage of PS-based solar cell under the condition of the sunlight irradiation and priori to sunlight irradiation in the purpose of observing clearly the photovoltaic effect possessed by the PS based solar cell. Judging by the results obtained in this paper, we can safely draw the conclusion that porous silicon is a good candidate material for the preparation of solar cell, that is to say that our study is giving high hope for the industrial production of high efficient PS-based thin film solar cells.

Abstract: Large-area silicon nanowire arrays (SiNWs) were prepared by etching silicon substrate in HF/AgNO3 system solution at near room temperature. Morphology of SiNWs was characterized by scanning electron microscopy. The results showed that morphology of SiNWs could be influenced by solution ratio, temperature and reaction time in the hydrothermal system. The length of SiNWs was about 30-40 μm, and the diameter of SiNWs was in the range of 100-300 nm. SiNWs owned strong optical absorption capacity and could be used for application in solar cell.

Abstract: Solid state photovoltaic cells have been fabricated using a ruthenium dye complex as a sensitizer, and poly[2-methoxy-5-(2-ethyl-hexyloxy)-phenylene vinylene] (MEH-PPV) as a hole transporting layer. A compact TiO2 layers with no pores has been introduced to prevent charge losses related to back reactions. The photovoltaic properties of MEH-PPV/dye coated TiO2 electrodes and MEH-PPV coated TiO2 electrodes with and without using compact TiO2 layers were investigated. The compact TiO2 layer increased the current from 0.09 mA/cm2 to 0.4 mA/cm2. Further improvement in current was achieved by inserting a dye interlayer between nanoporous TiO2 and MEH-PPV. In this case, the current increased up to 2 mA/cm2 yielding an efficiency of 0.3 %.

Abstract: Dye-sensitized solar cells (DSSC) are currently attracting widespread interest for the conversion of sunlight into electricity because of their low cost and high efficiency. In these cells, photo-anode is one of the key components for high power conversion efficiencies. In this paper, TiO2 nanopowders were prepared by the non-hydrolytic sol-gel method using TiCl4 as precursor, absolute ethanol and isopropanol as oxygen donor. Several different TiO2 nanopowders were used to fabricate TiO2 solar cells, and properties of TiO2 solar cells were characterized. The solar cell prepared with grainsize 50~80nm TiO2 nanopowders generated a short-circuit photocurrent of 13.17 mA/cm2, an open-circuit photovoltage of 789 mV, a fill factor of 69.8% and the efficiency of 7.25% under the light intensity of 100 mW/cm2.