Efficiency Enhancement in Organic Solar Cells by Use of Cobalt Phthalocyanine (CoPc) Thin Films.

Cobalt phthalocyanine (CoPc) nano thin films have been introduced as a hole buffer layer in organic solar cells with active layer of Poly(3-hexylthiophene) (P3HT) and [6,6]-phenyl-C61-butyric acid methyl ester (PCBM). The surface morphology and opto-electrical properties of the CoPc thin films have made it an applicable materials for organic solar cells. The nano-thin films of CoPc are continuously distributed over the studied area and the roughness are around 5 to 7 nm for all thickness. The dominant optical absorptions are in the visible range of wavelengths 500 to 800 nm. The CoPc buffer layer is suitable for energy level matching in energy level diagram and enhances the absorption spectrum as well, which facilitate the charge carrier generation, increases charge transport, decreases charge recombination, hence enhance the all device parameters short circuit current density (Jsc), open circuit voltage (Voc) and fill factor (FF). The solar cells efficiency increases by ˜70% and the fill factor increases by ˜45% in comparison to the standard cells. The increase in efficiency and the fill factors of the solar cells may also be attributed to the increasing of shunt and lowering the series resistance of the cells. The cole-cole plots of the devices may be modeled in electrical circuit as a single parallel resistance Rb and capacitance Cb network with a series resistance Rc.

Fabrication of transparent Al:LiF composite/MoO3 interconnecting layers for tandem white organic light emitting devices.

We report transparent Al:LiF composite/molybdenum oxides (MoO3) as interconnecting layers for tandem white organic light emitting diodes (WOLEDs) consisting of blue and red phosphorescent unit devices. The Al:LiF (3 nm)/MoO3 (10 nm) interconnecting layers show a high transmittance, good carrier generation and injection capability for tandem WOLEDs. The performance of tandem WOLEDs is sensitive to the LiF doping concentration, which is mainly attributed to the difference in efficiency of carrier injection into the adjoining electroluminescent units. For 10~20% LiF concentration, the external quantum efficiency of tandem device is almost equal to the sum of the efficiencies of blue and red OLEDs at high current density; furthermore, a small variation of Commission Internationale de l'Eclairage (CIE) coordinates with the current density is obtained.

Study of buffer layer thickness on bulk heterojunction solar cell.

We studied the effect of the buffer layer (molybdenum-oxide (MoO3)) thickness on the performance of organic solar cell based on blends of poly(3-hexylthiophene) (P3HT) and [6,6]-phenyl-C61 butyric acid methyl ester fullerene derivative (PCBM). The thickness of MoO3 was varied from 1 nm to 30 nm for optimization of device performance. The photocurrent-voltage and impedance spectroscopy were measured under dark and AM1.5G solar simulated illumination of 100 mW/cm2 for exploring the role of the buffer layer thickness on carrier collection at an anode. The MoO3 thickness of the optimized device (efficiency approximately 3.7%) was found to be in the range of 5 approximately 10 nm. The short-circuit current and the shunt resistance decrease gradually for thicker MoO3 layer over 5 nm. The device can be modeled as the combination of three RC parallel circuits (each one for the active layer, buffer layer and interface between the buffer layer and the active layer) in series with contact resistance (Rs approximately 60 ohm).