In this contribution, we present a new hybrid solar cell design. CuInS2 nanoparticles were synthesized using a low temperature colloidal route with organic surfactants to form an inorganic nanoporous hole transporting electrode. A soluble fullerene derivate PCBM (1-(3-methoxycarbonyl)-propyl-1-1-phenyl-(6,6) C61) was used for electron transport. We investigated the photovoltaic performance of the cells consisting of these CuInS2 and PCBM bilayers with and without a surface-adsorbed RuL2(NCS)/TBA(2:2) dye complex(where L= 2,2'-bipyridyl-4,4'-dicarboxylic acid; TBA= tetrabutylammonium). The cells containing the dye showed an improved photovoltaic response.
Efficient organic photovoltaic devices show many interesting properties, but share a common drawback, namely their instability in atmosphere. We report on a shelf lifetime study of solar cells based on blends of two widely used polymeric semiconductors with 1-(3-methoxycarbonyl) propyl-1-phenyl[6,6]C61 (PCBM), encapsulated in a new flexible and transparent poly(ethylene naphthalate) (PEN)-based ultra-high barrier material. The barrier coating is entirely fabricated by plasma enhanced chemical vapor deposition (PECVD). The conjugated polymers used are poly(2-methoxy-5-(3',7'-dimethyloctyloxy)-1,4-phenylene-vinylene) (MDMO-PPV) and poly(3-hexyl)thiophene (P3HT). We have observed in this work that the encapsulation raises the shelf lifetime (50 % of the initial
efficiency) from a few hours into the range beyond 3,000 hours for MDMO-PPV based devices. Using the more stable P3HT, the lifetime could be increased to approximately 6,000 hours, or more than eight months.
Photo-induced phenomena were investigated in photoresposive organic field-effect transistors (photOFETs) based on conjugated polymer/fullerene solid-state mixtures as active semiconductor layer and divinyltetramethyldisiloxane-bis(benzocyclobutene) (BCB) as gate dielectrics. The devices were characterized both in under dark showing n-type transistor behaviour with linear and saturated mobility of 1.7 x 10-3 cm2/Vs and 2.7 x 10-2 cm2/Vs respectively, and under white light illumination condition, where large shifts in the threshold voltage in the transfer characteristics were obtained. A typical phototransistor behaviour in a wide range of illumination intensities are observed in these devices.
Photophysical studies and photovoltaic devices on a low bandgap, high charge-carrier-mobility Poly(Thienylene
Vinylene) (PTV), prepared from a soluble precursor polymer synthesised via the 'dithiocarbamate route', are reported.
In composites with an electron acceptor ([6,6]-phenyl C61- butyric acid methyl ester (PCBM), a soluble fullerene
derivative) photoinduced absorption (PIA) characteristic for charged excitations together with photoluminescence (PL)
quenching are observed indicating photoinduced electron transfer. The "bulk heterojunction" photovoltaic devices using
PTV and PCBM composites show short circuit currents up to 4 mA/cm2 under AM 1.5 white-light illumination. The
photocurrent spectrum of the photovoltaic device shows an onset at about 1.65 eV (750 nm) which corresponds to the
absorption spectrum of the polymer.
In this work we study the internal electric field (Vint) present in devices based on an intrinsically semiconducting
polymer. Intermediate layers between the indium-tin-oxide and Al electrodes and the photoactive layer are
able to influence and alter this electric field. The two commonly used intermediate layers, namely poly(3,4-
ethylenedioxythiophene) doped with poly(styrenesulfonate) (PEDOT:PSS) and LiF, are subject of this study.
Their influence is studied with Electroabsorption (EA) spectroscopy as well as transient photocurrent measurements
under applied bias. While PEDOT:PSS has no significant influence on Vint, introducing LiF increases
Vint close to the bandgap of the studied semiconducting polymer. However, using PEDOT:PSS directly influences
the spectral EA response. The interface between PEDOT:PSS and the conjugated polymer is studied by
impedance spectroscopy. We interpret the results in terms of the presence of charges at the interface.
The covalent linking of acceptor molecules to electron donating conjugated polymer is an approach for the development of new photoactive materials for the fabrication of organic photoelectric conversion devices. With this strategy we have designed a polyalkylthiophene copolymer series containing in the side chain anthraquinone molecules as electron acceptor. The peculiar features of the copolymers are the good processability and the ease in tailoring the content of acceptor moieties. Their potential use as photoactive materials is investigated in terms of the photoinduced charge transfer properties, studied by FTIR photoinduced absorption and Light Induced Electron Spin Resonance spectroscopies. The results indicate the photoinduced electron transfer from the polythiophene backbone to the anthraquinone substituents and its tunability by changing the content of acceptor molecules. The photovoltaic response of these polymers is also discussed.
Information on doping- and photoinduced phenomena and processes in materials used in organic polymeric photovoltaic systems (plastic solar cells) can be obtained using infrared spectroscopy. The methods and results for the identification of doping- and photoinduced charge carriers, investigation of charge carriers in electrochemical systems, and studies on degradation processes are shown.
Results of in situ Fourier transform infrared attenuated total reflection (FTIR-ATR) spectroscopy during electrochemical oxidation processes (electrochemically induced doping) as well as by photoinduced infrared absorption spectroscopy (photoinduced doping) of polyparaphenylenevinylene (PPV) are presented. Infrared active vibrational bands in the lower energy part of the infrared spectrum and infrared absorption due to electronic transitions at higher energies are observed and compared. The electrochemical doping of PPV occurs in two potential regions. In the `low doping' region, the difference spectra obtained by in situ FTIR-ATR spectroscopy are similar to spectra obtained by chemical doping. In the `high doping' region, the spectral behavior is different to the `low damping' region and shows a higher similarity to the photoinduced absorption spectrum.