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Although silicon CMOS has been the process of choice for many uses in optoelectronic industry, its use for IR sensitive optoelectronic devices is limited to below ~1100 nm by the 1.11 eV band-gap of silicon. Extending the optical sensitivity range of silicon devices up to several microns, while maintaining good sensor responsivity, short rise and fall times, and maintaining the CMOS process compatibility, would be of great importance for possible telecom or other optoelectronic uses. Heterojunction interfaces between organic thin films and silicon often show synergetic advantages regarding certain properties. We present our work on optoelectronic devices based on heterojunctions of silicon and organic thin films of hydrogen- bonded pigment tyrian purple (6, 6′- dibromoindigo) formed by vacuum evaporation. Tyrian purple is an ambipolar organic semiconductor with an optical band-gap of 1, 9 eV and electron and hole mobilities of 0, 4 cm2/Vs, which forms rectifying junctions with p-doped silicon. Even though the band-gap of both materials in the heterojunction is relatively high, our devices show sub silicon- bandgap IR sensitivity up to 2500 nm with responsivity of ~5 mA/W in the telecom C-band. Finally, we show that micro- and nano- structuring of silicon substrates prior to vacuum evaporation of organic layer significantly improves the responsivity of hybrid silicon-organic photodiodes.

Maximization of the power conversion efficiency (PCE) in nanostructured silicon/ PEDOT:PSS hybrid solar cells is an active area of photovoltaic research, due to the reduced thermal budget in production of such devices in comparison to conventional silicon solar cells [1]. Surface passivation of silicon at silicon/organic interface was found to be essential for high efficiency of silicon-based photovoltaics. Surface defects and dangling bonds significantly increase the recombination rate of minority carriers, may pin the Fermi level and cause undesirable band bending at silicon interfaces [2]. Passivation methods for planar silicon surfaces that are currently available [3] are not always compatible with the nanostructured and hybrid organic/inorganic devices, for which appropriate passivation should be developed. Measuring the state of surface passivation is essential in this process. We present a method for the characterization of surface passivation of silicon by simultaneous band gap photoluminescence and Raman spectroscopy.

Inorganic semiconductor materials have for a long time been a standard member of electronic devices ecosystem, with silicon being the material of choice for most applications. Lately, organic semiconductors have become more visible not only for scientists but also to general public, with applications such as OLED screens and organic photovoltaic devices becoming a part of our daily lives. Introducing nanostructuring in both types of materials has proven to be advantageous for their properties and applications. Heterojunction interfaces between organic and inorganic thin films in devices show promise in using the advantages of both materials simultaneously. We present our work on devices based on heterojunctions of porous silicon formed by anodisation in HF- based electrolytes and organic thin films formed by vacuum evaporation. For the inorganic part of the heterojuction we choose porous silicon due to its compatibility to established CMOS technology and its enormous surface area being presented to thin organic films. For organic part of the junction we investigated the applicability of various organic semiconductor thin films for optoelectronic and biosensing applications. Our porous silicon- based devices show enhancement in optical response in comparison to devices based on bulk silicon.

We report here the synthesis of a novel branched quasi-dendric system, 9,9'-(9,9'-dihexylfluorene-2,7-diyl)bis[3,6-bis(2,5-bis(2-thienyl) pyrrol-1-yl)carbazole], (FCSNS), in four steps, followed by coating onto an ITO-coated glass surface by an electropolymerization process to give a very stable cross-linked polymeric film (poly-FCSNS). The yellowish-green color of this film in its neutral state changed reversibly to black upon oxidation. An electrochromic device, assembled in the sandwich configuration [ITO/anodically coloring polymer (poly-FCSNS)//gel electrolyte//cathodically coloring polymer/(PEDOT)/ITO], exhibited a relatively short response time (about 1 s), a high redox stability, and a high coloration efficiency (1624 cm(2) C-1). In addition to electrochromic studies, organic light-emitting diode (OLED) work was also carried out using FCSNS. A multilayer OLED having a configuration of ITO/PEDOT:PSS/FCSNS/Alq(3)/LiF : Al was fabricated, and it showed a turn-on voltage of approximately 6 V and exhibited a bright green emission with a luminance of 3700 cd m(-2). The maximum luminous efficiency was found to be 2.0 cd A(-1) at 14 V and 11.75 mA cm(-2). The emitted light from the OLED device is green, and has the color coordinates of (x, y) (0.33, 0.54) according to CIE. Electrochemical and optical properties were also studied by using cyclic voltammetry, UV-Vis absorption and fluorescence spectroscopy, respectively.

D-A-D-type polymers are of high interest in the field of photovoltaics and electrochromism. In this study we report the synthesis and electrochemical properties of PPyBT along with its photophysical properties and photovoltaic performance. PPyBT is soluble in common organic solvents and both n- and p-type dopable, which is a desired property for conjugated polymers. During electrochemistry studies, the onset potentials of the polymer were determined as +0.2V for oxidation and -1.4V for reduction. Using these values, HOMO and LUMO energy levels were calculated. The photovoltaic properties of PPyBT were also studied. PL studies showed that there is a charge transfer between PPyBT (donor) and PCBM (acceptor).

Novel hole-transporting dendrimeric molecules containing dioctylfluorene, spirobi(fluorene) and spiro(cylododecane-fluorene) as the core unit and different numbers of carbazole and thiophene moieties as the peripheral groups are synthesized. All the dendrimers are characterized by H-1 NMR, C-13 NMR, FTIR, UV-vis, PL spectroscopy, and MALDI-TOF. They are thermally stable with high glass transition and decomposition temperatures and exhibit chemically reversible redox processes. They are used as the hole-transporting layer (HTL) material for multilayer organic light emitting diodes (OLEDs) with a low turn-on voltage of around 2.5 V and a bright green emission with a maximum luminance of around 25400 cd m(-2).

Org. solar cells based on interpenetrating networks of conjugated polymer donors and fullerene-based acceptors with MA 1.5 efficiencies up to 3% were presented recently. For further improvement of the efficiency, the absorption of the solar light should be increased. This can be done by matching the active layer absorption better to the terrestrial solar emission spectrum and by increasing the absorption coeff. In this contribution the authors present a combined spectroscopic and device study of novel materials that extend the absorption to the red. The systems studied are, among others, low bandgap polymers as electron donors or dye sensitized fullerene compds. The photophys. properties are studied by excited state spectroscopy and the materials are discussed with regard to their suitability for efficient photoinduced charge generation. The photovoltaic activity is demonstrated by photocurrent action spectra as well as by AM 1.5 efficiencies of prototype devices made using these novel materials. [on SciFinder(R)]