In this and the following paper (Parts I and II, respectively), we discuss the properties of mixed donor-acceptor organic thin films and their application to organic solar cells. In Part I, we present a study of the material properties of mixed donor-acceptor thin films. Through optical absorption, x-ray diffraction, microscopy, and charge transport measurements, we determine the relationships among film microstructure, mixing ratio, and charge conduction in mixtures of two organic molecular species. We find that mixed layers of the molecular pair of 1:1 (by weight) copper phthalocyanine in C60 have electron and hole mobilities reduced by more than one order of magnitude compared to corresponding films of pure composition. In Part II, we demonstrate that the performance of organic hybrid planar-mixed heterojunction photovoltaic cells based on a mixed donor-acceptor molecular layer sandwiched between the donor and acceptor layers of homogeneous composition can have improved performance over conventional pl...

Mixed donor-acceptor molecular heterojunctions for photovoltaic applications. I. Material properties

This paper describes a simple, vapor-phase route to the synthesis of metastable α-phase copper-phthalocyanine (CuPc) single-crystal nanowires through control of the growth temperature. The influence of the growth temperature on the crystal structures, morphology, and size of the CuPc nanostructures was explored by XRD, optical absorption and Transmission Electron Microscopy (TEM). α-CuPc nanowires were successfully incorporated as active semiconductors in field-effect transistors (FETs). Single nanowire devices exhibited the carrier mobilities and current on/off ratios as high as 0.4 cm2/Vs and > 104, respectively, rendering them useful for organic photovoltaic cells, organic light-emitting diodes, field-effect transistors, memories and gas sensors

Metastable Copper-Phthalocyanine Single-Crystal Nanowires and Their Use in Fabricating High-Performance Field-Effect Transistors

Effects of annealing on the morphology and optical property of copper (II) phthalocyanine nanostructured thin films

Effect of substrate temperature on microstructure of copper phthalocyanine (CuPc) thin films deposited on quartz and polycrystalline alumina substrates by vacuum sublimation technique has been studied. The films undergo a transition from α phase at lower substrate temperatures to β phase for temperatures above 200 °C. A simultaneous change in morphology from granular to nano-fibrous films was observed. Resistance of α phase films increased by more than one order of magnitude on initial application of electric field requiring stabilization for several hours, while β phase films did not show any drift. This behavior was attributed to oxygen absorption/desorption under applied field. Sensitivity of films for detection of NO 2 gas at room temperature was found to be higher for films in the α-phase with nano-fibrous morphology. Methodology was devised for measurement of NO 2 concentration in ppm range with good response and recovery times. With this methodology, the sensors showed very good stability in response (at room temperature) for a period of 1 year.

NO2 sensors with room temperature operation and long term stability using copper phthalocyanine thin films

Phthalocyanine compounds have been widely investigated as candidate materials for technological applications, which is mainly due to their thermal stability and possibility of processing in the form of thin films. In most applications, the controlled growth of thin films with high crystalline quality is essential. In this study, zinc phthalocyanine (ZnPc) thin films were prepared by evaporation on glass and Au-coated glass substrates with subsequent annealing at different temperatures in ambient atmosphere. The morphological and structural features of 80 nm thick zinc phthalocyanine films were investigated, evidencing an α → β phase transformation after annealing the films at 200 °C, as indicated by UV–Vis spectroscopy and FTIR analyses. A better uniformity of the annealed films was also evidenced via AFM analysis, which may be of importance for applications where film homogeneity and excellent optical quality are required.

The effects of temperature on the molecular orientation of zinc phthalocyanine films

Effects of substrate temperature on copper(II) phthalocyanine thin films

We report the current transport properties of an organic conductor/superconductor tunnel junction as a high-Tc superconducting three terminal device. The organic copper (II) phthalocyanine (Cu–Pc) layer was used for a polaronic quasiparticle (QP) injector. The junction was investigated in the dark and under ultraviolet radiation. The injection of polaronic QP from the Cu–Pc interlayer into a superconductor Bi2Sr2CaCu2O8+δ (BSCCO) thin film generated a substantially larger nonequilibrium effect as compared to the normal QP injection current. The tunneling spectroscopy of a Cu–Pc/BSCCO junction exhibited a zero bias conductance peak, which may be interpreted as Andreev reflection at a Cu–Pc/d-wave superconductor junction.

Jungyoon E

Papers

Effects of substrate temperature on copper(II) phthalocyanine thin films

Polaronic quasiparticle injection in organic copper (II) phthalocyanine/Bi2Sr2CaCu2O8+δ tunnel junctions