H. Rost

Crystal network formation in organic solar cells

We have studied the effects of annealing on performance and morphology of photovoltaic devices using blends of two organic semiconductors: a conjugated polymer and a soluble perylene derivative. The efficiency of such photovoltaic cells has been determined. The effect of temperature on blend morphology has been investigated for actual device films. Annealing leads to the formation of micron size perylene crystals and an enhancement of the quantum efficiency. This enhancement has been attributed to the formation of an electron conducting perylene crystal network.

Analysis of deep levels in a phenylenevinylene polymer by transient capacitance methods

Transient capacitance methods were applied to the depletion region of an abrupt asymmetric n+−p junction of silicon and unintentionally doped poly[2-methoxy, 5 ethyl (2′ hexyloxy) paraphenylenevinylene] (MEH-PPV). Studies in the temperature range 100–300 K show the presence of a majority-carrier trap at 1.0 eV and two minority traps at 0.7 and 1.3 eV, respectively. There is an indication for more levels for which the activation energy could not be determined. Furthermore, admittance data reveal a bulk activation energy for conduction of 0.12 eV, suggesting the presence of an additional shallow acceptor state.

Photovoltaic properties of MEH-PPV/PPEI blend devices

Abstract We report on the photophysical properties of blends of poly(2-methoxy-5-(2′-ethyl-hexyloxy)- p -phenylene vinylene), MEH-PPV, and perylene bis(phenethylimide), PPEI. Highly efficient quenching of photoluminescence (PL) efficiency was observed. We have measured the photocurrent response of an MEH-PPV/PPEI blend in a sandwich cell between indium tin oxide (ITO) and aluminium electrodes. The external quantum efficiency (EQE) is enhanced considerably with regard to single layer MEH-PPV devices.

Light-emitting electrochemical cells based on poly(p-phenylene vinylene) copolymers with ion-transporting side groups

We present the electro-optical characteristics of LECs based on two copolymers derived from poly(p-phenylene vinylene), DB-alt-BTEM-PPV and BDMOS-co-BTEM-PPV, having ion-transporting side groups. We find typical LEC behaviour upon addition of lithium triflate. Addition of poly(ethylene oxide), PEO, improves the EL efficiency, but the response time increases. We discuss these observations on the basis of PEO-induced phase separation.

Electronic levels in MEH-PPV

pn-Junctions of MEH-PPV on top of heavily doped n-type silicon were used in electrical measurements. Through deep-level transient-spectroscopy (DLTS)-like measurements, four traps (two majority and two minority traps) could be identified on top of the shallow acceptor level responsible for conduction. Furthermore, evidence is found for interface states.

Minority-carrier effects in poly-phenylenevinylene as studied by electrical characterization

Electrical measurements have been performed on poly[2-methoxy, 5 ethyl (2′ hexyloxy) paraphenylenevinylene] in a pn junction with silicon. These included current–voltage measurements, capacitance–voltage measurements, capacitance–transient spectroscopy, and admittance spectroscopy. The measurements show evidence for large minority-carrier injection into the polymer possibly enabled by interface states for which evidence is also found. The shallow acceptor level depth (0.12 eV) and four deep trap level activation energies (0.30 and 1.0 eV majority-carrier type; 0.48 and 1.3 eV minority-carrier type) are found. Another trap that is visible at room temperature has point-defect nature.

Determination of deep and shallow levels in conjugated polymers by electrical methods

Abstract Conjugated organic semiconductors have been submitted to various electrical measurement techniques in order to reveal information about shallow levels and deep traps in the forbidden gap. The materials consisted of poly[2-methoxy, 5 ethyl (2′ hexyloxy) paraphenylenevinylene] (MEH-PPV), poly(3-methylthiophene) (PMeT), and α -sexithienyl ( α T6) and the employed techniques were IV, CV, admittance spectroscopy, TSC, capacitance and current transients.

Novel luminescent polymers

Abstract We report the synthesis and luminescence properties of poly[2,5-bis(dimethyloctylsilyl)-l,4-phenylene vinylene)](BDMOS-PPV) 4 and its statistical copolymer poly[2,5-bis(dimethyloctylsilyl)-1,4-phenylene vinylene)]-co-[2,5-bis(trisethoxymethoxy)-1,4-phenylene vinylene)] (BDMOS-BTEM-PPV) 6 with units carrying ion-transporting triethoxy side-chains. The highly fluorescent polymers were synthesised by dehydrohalogenation polymerisation and show promise as materials for LED and LEC fabrication.

Luminescence properties of a PPV-based statistical copolymer with glyme-like side groups

The orange emitting statistical copolymer, poly[2,5-bis(dimethyloctylsilyl)-1,4-phenylene vinylene)]-co-[2,5-bis(trisethoxy-methoxy)-1,4-phenylene vinylene)], has a photoluminescence efficiency of about 17%. Light-emitting diodes with calcium cathodes exhibit luminances up to 1300 cd/m 2 with an efficiency of 0.5 cd/A. ITO/copolymer+lithium triflate/Al devices exhibit typical light-emitting electrochemical cell behaviour.