The photovoltaic properties of dye-sensitized solar cells (DSCs) based on fluorine doped tin oxide (FTO) and Ti substrates were investigated. The sheet resistances of the substrates were correlated to the photovoltaic properties. The efficiency of the Ti substrate based DSC was higher than that of the FTO substrate based DSC, due to a high fill factor (FF). To minimize the internal resistance of the DSCs, Ti plate was used as a support for nanocrystalline TiO2, because of its low sheet resistance. As the light was absorbed by the electrolyte layer, the incident photon to current efficiency (IPCE) values decreased in the range between 400-600 nm. The electrolyte concentrations were optimized to obtain a higher cell performance. When using an electrolyte composed of 0.02 M I2, 0.2 M LiI, and 0.5 M 4-tert-butylpyridine, an efficiency of 4.98% was obtained for the Ti substrate based DSC with a short circuit current density (Jsc) of 11.25 mAcm-2, an open circuit voltage (Voc) of 0.692 V, and a FF of 0.639. The effect of the cell size on the photovoltaic properties was also investigated. The rate of decrease in a FF and efficiency with increase in the cell size was lower for the Ti substrate based DSCs than the FTO substrate based DSCs. This result indicates that Ti plate is a potential candidate for production of large DSCs.

A high performance semitransparent cathode is one of the major impediments to the high performance semitransparent and tandem organic photovoltaic (OPV) cells. In this work, we discuss the possible designs of semitransparent cathode to improve the performance of semitransparent OPV cells. The optical properties of the poly(3-hexylthiophene) (P3HT): 1-(3-methoxycarbonyl)-propyl-1-phenyl-(6,6)C61 (PCBM)-based OPV cells were studied by the optical admittance analysis. The performance of the OPV cells made with an opaque Ca(10nm)/Ag(100nm) cathode and a semitransparent Ca(10nm)/Ag(10nm)/ITO cathode are discussed. The interfacial properties at the cathode/organic interface were analyzed using the time-of-flight secondary ion mass spectroscopy (TOF-SIMS). The TOF-SIMS depth profile revealed that calcium oxide formed at the Ca/organic interface in semitransparent OPV cells, which was induced by the ITO sputtering process. It shows that the presence of calcium oxide at the organic/cathode interface could be the main reason resulting in a poor fill factor of a semitransparent OPV cell (∼23%) as compared to that of a reference cell (∼43%).

Electrochemical oxidation of tetrakis-5,10,15,20-(4-aminophenyl)porphyrin (TAPP) on fluorine-doped tin oxide electrodes leads to a conductive polymeric film (poly-TAPP) with a nanostructured fibrous morphology. The nanofiber structure and growth rate are enhanced by the addition of pyridine (5 - 15%) to the dichloromethane electrochemical solution. Electropolymerization in the absence of pyridine leads to a more highly bundled poly-TAPP structure with a spectrum indicative of protonated porphyrin units. Testing of poly-TAPP electrodes in an electrochemical iodide cell and in a 1-(3-methoxycarbonyl)propyl-1-phenyl[6,6]C61 (PCBM) integrated solid state photovoltaic cell indicates modest photoactivity.

Structural, electrical and optical characterizations of nanostructured ZnO thin films used as photosensitized electrodes in photovoltaic cells applications are reported. Nanostructured ZnO thin films were deposited on optical glass substrates by pulsed-laser deposition (PLD), their structure and morphology being optimized for photovoltaic applications. Structural analysis of the samples by X-ray diffraction revealed that the films consist of a hexagonal-close-packed wurtzite type phase ZnO, (001) preferentially oriented in the growth direction. The ZnO films are highly transparent in visible region of solar spectrum, and exhibit electrical resistivities in the range 10-4 - 10-2Ω.m

A stable organic molecular radical, 2,2,6,6-tetramethyl-1-piperidinyloxy (TEMPO), has been electrochemically studied and employed as a new redox mediator in nanocrystalline TiO2 dye-sensitized solar cells (DSCs) when it is doped with nitrosonium tetrafluoroborate (NOBF4). Reasonable photocurrents can be achieved despite of driving force of only 0.2 eV for the TEMPO/TEMPO+ system as compared to 0.6 eV for the iodide/triiodide redox system. Judicious selections of a 5 µm photoanode made from TiO2 mesoscopic particles (60 nm in diameter) and an organic sensitizer with high molar extinction coefficient yield an overall power conversion of 5.0 % under AM 1.5 illumination at 100 mW cm-2 and an incident photon-to-current conversion efficiencies (IPCE) in excess of 50 %.

The performance of organic solar cells based on the blend of regioregular poly(3-hexylthiophene) (P3HT) and phenyl-C61-butyric acid methyl ester (PCBM) is strongly influenced by the morphology of the active layer on the nanoscale level. X-ray diffraction (XRD) and Transmission Electron Microscopy (TEM) measurements show that ordering of P3HT plays a key role in optimizing the photovoltaic performance. It is demonstrated that the natural tendency of regioregular P3HT to crystallize is disturbed by the addition of PCBM. The crystallinity of the photo-active blend is typically restored by an annealing procedure resulting in improved device performance, characterized by a spectral broadening of the optical absorption.

The morphological changes upon annealing of the P3HT:PCBM blends are accompanied by electrical changes as shown in charge carrier mobility measurements. Space-charge limited current measurements have been performed in hole-only devices with various P3HT:PCBM blend ratios. The mobility before and after annealing is compared and from temperature dependent measurements the width of the density of states distribution (DOS) is determined. The hole mobility in pristine P3HT remains practically unaffected by the annealing treatment. The as-produced P3HT:PCBM blends on the other hand, with a more disordered P3HT phase, have a much lower hole mobility. Annealing is capable of increasing the P3HT ordering with as a result an orders of magnitude larger hole mobility, approaching the value found in pristine P3HT. The DOS bandwidths are affected similarly. In the as-produced blend films a value of 100 meV is found, larger than in the annealed films, there reaching a value around 70 meV similar as in pristine P3HT. Variation of the processing solvent demonstrated however that an optimized morphology and charge transport situation can also be obtained without an additional annealing step. It is shown that in that case the as-produced active layer has already a favorable crystalline morphology. We argue that the high boiling point of the solvent plays an important role in this by influencing the evaporation speed during deposition of the photo-active blend. Further proof is delivered that indeed slowing down the evaporation speed can beneficially influence the solar cell performance. Power conversion efficiency over 4% has been achieved in this way.