Rutile TiO2 films as electron transport layer in inverted organic solar cell

Titanium dioxide (TiO2) thin films were prepared by sol–gel spin coating method and deposited on ITO-coated glass substrates. The effects of different heat treatment annealing temperatures on the phase composition of TiO2 films and its effect on the optical band gap, morphological, structural as well as using these layers in P3HT:PCBM-based organic solar cell were examined. The results show the presence of rutile phases in the TiO2 films which were heat-treated for 2 h at different temperatures (200, 300, 400, 500 and 600 °C). The optical properties of the TiO2 films have altered by temperature with a slight decrease in the transmittance intensity in the visible region with increasing the temperature. The optical band gap values were found to be in the range of 3.28–3.59 eV for the forbidden direct electronic transition and 3.40–3.79 eV for the allowed direct transition. TiO2 layers were used as electron transport layer in inverted organic solar cells and resulted in a power conversion efficiency of 1.59% with short circuit current density of 6.64 mA cm−2 for TiO2 layer heat-treated at 600 °C

Enhancement of power conversion efficiency of P3HT : PCBM solar cell using solution processed Alq3 film as electron transport layer

Solution-processed thin films of tris(8-hydroxyquinoline)aluminum (Alq3) have been produced and examined as an electron transport layer in P3HT:PCBM bulk heterojunction organic solar cells. UV–Vis absorption, XRD, SEM and current density–voltage (J–V) measurements both in dark and under illumination have been carried out. Absorption spectra of the active layer show typical P3HT:PCBM absorption features with a maximum absorption peak around 500 nm and two vibronic shoulders around 550 and 600 nm which were attributed to the inter-chain stacking of P3HT. Furthermore, XRD measurements revealed that the co-solvent processed film shows better crystallinity than the mono-solvent film. On the other hand, SEM images show a clear pinholing effect in the DCB-processed film which may cause leakage current that reduces the fill factor and overall power conversion efficiency (PCE) of the organic solar cell (OSC). Alq3 absorption spectra show an absorption peak in the UV region, with an optical band gap of 2.83 eV. The incorporation of Alq3 films as an electron transport layer in ITO/PEDOT:PSS/P3HT:PCBM/Alq3/Al structure has resulted in a significant enhancement in the performance of the studied OSC devices. The use of mixed solvents of dichlorobenzene and chlorobenzene (DCB:DB) together with the inclusion of Alq3 layer has resulted in enhanced PCE which reached 3.92 %

Effect of variable ultrasonic frequencies on some physical properties of Iraqi palm fiber PVA composite

The palm fiber –PVA composite polymer membrane were prepared by solution casting method with different ratios of concentration in order to study the ultrasonic frequency affect on mechanical properties of this composite. Ultrasonic pulse technique of variable frequency (25,30,35,40,45 and 50 kHz) were performed ,some properties such as ultrasonic velocity, acoustic impedance ,bulk modulus ,transmittance and viscosity are decreasing with increasing frequency while absorption coefficient, relaxation time, compressibility and relaxation amplitude are increasing with increasing frequency .results shows that ultrasonic wave made degradation to the randomly coiled polymer chains ,when ultrasonic frequency increase there are more degradation that increasing the number of un-tie chains as a results of absorbing composite ultrasonic waves ,for this reason we pointed that palm fiber-PVA composite as a good ultrasonic absorber.PVA composite; mechanical properties; solution casting method; ultrasonic frequency

The effects of the PEDOT:PSS acidity on the performance and stability of P3HT:PCBM-based OSCs

The optical transmittance, electrical conductivity and morphology of PEDOT:PSS treated with ammonium hydroxide (NH4OH) have been investigated. Transmittance spectra of spun PEDOT:PSS layers were enhanced slightly as a result NH4OH treatment while surface of the films has exhibited variation in the roughness and an increase in the electrical conductivity. Improvement in the physical properties of PEDOT:PSS is shown to be the key factor in enhancing the power conversion effeciency (PCE) with values as high as 4% associated with high fill factor (FF) of 57%, open circuit voltage (VOC) of 0.64 V and larger short circuit current density (JSC) of 11 mA cm−2. Stabiltiy test of the devices has been carried out over a period of 2 months, when a device incorporating PEDOT:PSS with pH ~ 4 as the hole transport layer has shown an improved stability with a degredation in PCE in about 43% whereas JSC has decreased in about 20% compared to a device incorporating pristine PEDOT:PSS with PCE decreased in about 66% and JSC in about 50% over the stated period of test. These effects have been ascribed to the increased acidity of the hole transport layer

Efficient P3HT:PCBM bulk heterojunction organic solar cells; effect of post deposition thermal treatment

Organic solar cells based on P3HT:PCBM bulk heterojunction were prepared and subjected to post annealing at different temperatures (100, 120, 140, 160 and 180 °C). SEM, AFM as well as optical images have revealed that post deposition heat treatment has induced significant phase segregation between P3HT and PCBM which were found to result in growth of PCBM clusters on the films surface. The P3HT:PCBM absorption spectra were found to be blue shifted by 7 nm in films subjected to heat treatment at 160 °C and 180 °C. XRD data show a single diffraction peak at 2θ = 5.33 ± 0.23o for P3HT:PCBM films and was attributed to the edge-on arrangement of the (100) plane. Space charge limited conduction theory was employed to determine the charge carrier mobility; the highest obtained mobility was obtained for devices with active layers heat-treated at 140 °C. The change in the barrier height was derived from dark I–V. The variation in the metal–semiconductor contact between the Al electrode and P3HT:PCBM active layer were addressed and the barrier height has increased to form hole blocking contact and the ideality factor has decreased implying a decrease in the recombination rate. A direct relation between Fermi level, Vbi, and Voc was studied. Efficient device performance was ascribed to P3HT:PCBM layers which were subjected to post deposition heat treatment at 140 °C with PCE = 5.5 %, FF = 65.6 %, Jsc = 12.9 mA cm−2 and Voc = 0.65 V

Effect of dispersion of gold nanoparticles on the properties and alignment of liquid crystalline copper phthalocyanine films

The inclusion of hexadecylamine capped gold nanoparticles (AuNPs) into the ordered matrix of hexagonal columnar mesophase of copper phthalocyanine (CuPc) has been investigated. The effects of AuNPs on the liquid crystalline behaviour, optical and electrical properties of CuPc films is investigated by different physical methods. The molecules orientation in the films of CuPc and its composites with AuNPs, deposited on the surface of one substrate and between two electrodes, is studied by polarized Raman spectroscopy and polarized microscopy. It has been shown that thin films of the composites confined between ITO and Al electrodes are characterized by homeotropic alignment while no homeotropic alignment was observed in films deposited on ITO substrate with air constituting the upper interface. The I(V) dependences for the films confined between ITO and Al electrodes were measured. Appreciable enhancement of the DC conductivity is observed in the case of composites containing gold nanoparticles