In this work, OPVs with an active layer composed by P3HT (poly(3-hexylthiophene)) and PCBM ([6,6]-phenyl-C61- butyric acid methyl ester) was fabricated by spin coating technique and studied after post-thermal annealing. The devices were annealed at temperatures ranging from 150 °C to 175 °C, showing an increase in efficiency at 160 °C, decreasing after. In order to achieve a physical model for this behavior, dc and ac measurements, together morphology analysis was made and correlated. Under dc conditions, the overall figures of merit were measured and fitted to the physical models using genetic algorithms; by ac measurements, the capacitance and loss dependence on frequency were studied and equivalent circuit models were obtained. Capacitance – voltage behavior was also analyzed. The morphology of OPV active area film was investigated by Atomic Force Microscopy (AFM) in both tapping and current sensing methods. The OPVs exhibit efficiencies ranging from 1.2 to 3%, with fill-factors (FF) ranging from near 50% to near 70%. The relaxation frequencies can be correlated with the efficiency behavior, and with the micro electrical map obtained (and correlated with morphology) by AFM-current sensing. It was shown that how post-thermal annealing changes the micro electrical patterning and therefore, a suitable relationship with macroscopic behavior can be established.
OLEDs for lighting became of high relevance, although challenges in the uniformity and thermal effects. In this work, White-OLEDs with 16 cm2 emitting area was made with wide color temperature range (3200 K to 10500K) and color rendering index near 90. The CIE coordinates are stable with applied voltage. Thermal images shows 60°C in the center decreasing to 35°C at the border. This effect was study by a scalar electro-thermal model, considering the substrate, electrodes and organic layers. The thermal changing ratio in the series resistance and forward voltage obtained was of - 70 mΩ/°C and -10 mV/°C respectively.
We report chirped fiber Bragg gratings (CFBGs) photo-inscribed in undoped PMMA polymer optical fibre (POF) for the first time. The chirped polymer optical fiber Bragg gratings (CPOFBGs) were inscribed using an UV KrF excimer laser operating at 248 nm. The rectangular gauss laser beam was expanded to 25 mm in horizontal direction along the fiber core by a cylindrical lens, giving a total of 25 mm grating length. A 25 mm long chirped phase mask chosen for 1550 nm grating inscription was used. The laser frequency was 1 Hz with an energy of 5 mJ per exposure, exposing few pulses for each grating inscription. The reflection amplitude spectrum evolution of a CPOFBG is investigated as a function of the applied strain and temperature. Also, some results regarding to group delay are collected and discussed. These results pave the way to further developments in different fields, where POFs could present some advantages preferably replacing their silica counterparts.
One important key to improve the bulk-heterojunction photovoltaics (BHJs) is the fill-factor (FF). In this work, a study of the FF dependence factors on BHJs with an active layer of MEH-PPV / PCBM is made. The FF changes from 20% to 70%, depending on the current – voltage behavior and on the photovoltaic equivalent circuit parameters changes (parallel and series resistances, voltage open circuit, short circuit current and photocurrent). The efficiency changes from 1% to 5%. A theoretical simulation for FF optimization is made allowing a better understand of the physical process involved in the BHJ that modulates such parameter.
This work we presents a detailed result of Organic Light Emitting Diodes based on europium complex as emitting layer, the tris (dibenzoylmethane) – mono (4,7-dimethylphenantroline) europium (III) – Eu(DBM)3phen. The electrical d.c. and a.c. behavior is analyzed and correlated with the electroluminescence data. The electroluminescence spectra show the Eu3+ ion transitions, with the main emission at 612 nm. The driving voltage is about 20 V although the electrical current is only 0.1 mA (Wall Plug Efficiency up to 4×10-3 %). Under some conditions, emissions from others organic emitters can be observed. A model considering the charge confinement and the materials energy levels is proposed and discussed.
In this work we report for the first time the electroluminescence of two different kinds of rare earth complexes based
Organic Light Emitting Diodes, the Tb(ACAC)3bipy [Tris (acetylacetonate) - 2,2' - bipyridinyl - terbium(III)] and the
Eu(TTA)3bipy [tris(4,4,4 -trifluoro -1 - (2 - thienyl) -1,3 - butanediono - 2,2' - bipyridinyl - europium(III)]. In both
devices the corresponding electroluminescence spectrum is obtained (red for europium with (x,y) CIE coordinates near
(0.64, 0.34) and green for terbium near (0.28, 0.55) coordinates) at a driving voltage near 16 - 17 V with a maximum
electrical current of 1 mA. The Wall Plug Efficiency is about 10-3% in both cases.
In this work a detailed study of the electroluminescence of an Organic Light Emitting Diode based on Europium
Complex is studied as a function of the emissive layer thickness and growth rate evaporation. The device structure is
glass:ITO / TPD [N,N' - bis (3 - methylphenyl) - N,N' - diphenylbenzidine] / Eu(DBM)3phen [tris (dibenzoylmethane)
- mono (4,7-dimethylphenantroline) europium (III)] / Alq3 [aluminum - tris (8 - hydroxyquinoline)] / Aluminum. The
minimum driving voltage is about 15 Volts although the electrical current is about only 2 mA (wall plug efficiency up to
0.002 %). The electroluminescence spectra and external efficiency are clearly dependent on the Eu (DBM)3phen layer
thickness and growth rate evaporation. This results in a strong color change (CIE coordinates). With these results, a
model for the device opto-electrical behavior is presented, allowing the device final optimization.