We report on the realization of high-efficiency bulk heterojunction PV devices based on P3HT/PCBM on transparent
plastic substrates, from one elementary cell to large area modules, and we compare with results obtained on glass. The
first target consists in the optimisation of the processing parameters in order to obtain the highest possible Power
Conversion Efficiency (PCE) values for individual cells. We have reached PCE close to 4% with small dispersion on
plastic substrates for cells of 0.28 cm2 active area, compared to 5% on glass. Modules of multiple cells are then
elaborated on 5x5 cm substrates with a design aimed to minimize ohmic losses, and interconnection resistances. For
glass module, with 12 individual cells on a 5x5 cm2 substrate we obtain PCE of 3.26 % (12.4 cm2 active surface). Larger
modules with active area up to 35 cm2 exhibiting PCE of 2.8 % and open circuit voltage higher than 6V are also
demonstrated for glass, approaching the requirements for commercial electronic applications. On PET, record efficiency
of 2.85 % is obtained for a 8.8 cm2 module and PCE of 2.52 % is demonstrated for a large area module with 53 cm2
active surface. The influence of the geometric parameters of the individual cells and their type of connection (parallel or
series) on the module characteristics is also discussed.
This article describes a method to have a better knowledge of barrier performances needed for encapsulating
materials, particularly in the case of organic solar cells devices. We have developed a high sensitivity
permeameter which enables simultaneous measurements of water and oxygen permeation. Various polymers and
inorganic coatings on polymer substrates have been measured. Experimental barrier parameters have been
plotted considering the steady and transient states of permeation curves and compared to theoretical values. In
addition, we have performed ageing experiments on encapsulated organic solar cells to establish a barrier
requirement directly related to the device. Finally, we have performed such experiments using different cathode
materials and encapsulating materials.
Organic photovoltaic represents an emerging technology thanks to its ability to give flexible, light weight and large-area
devices, with low production cost by simple solution process or printing technologies. But these devices are known to
exhibit low resistance to the combined action of sunlight, oxygen and water. This paper is focused on the behaviour of
the active layer of the devices under illumination in the presence and absence of oxygen.
The monitoring of the evolution of the chemical structure of MDMO-PPV submitted to accelerated artificial ageing
permitted the elucidation of the mechanisms by which the polymer degrades. Extrapolation of the data to natural ageing
suggested that, if well protected from oxygen (encapsulation),
MDMO-PPV:PCBM based active layer is
photochemically stable for several years in use conditions. In addition the charge transfer between the two materials was
observed to remain efficient under exposure.
The study of P3HT:PCBM blends allowed to point out the Achilles heel of P3HT towards the impact of light. In
addition, P3HT:PCBM blends were shown to be much more stable under illumination than MDMO:PCBM blends.
Preliminary results devoted to the AFM monitoring of the morphological modifications of P3HT:PCBM blends under
the impact of light are also reported.
The synthesis, spectroscopic characterization and fluorescence quenching efficiency of a polymer (PSt-NI) and a low molecular weight molecule (NI) containing the 4-(N, N disubstituted)amino-N-2,5ditertiobutylphenyl-1,8-naphthalimide chromophore are reported. Similar spectroscopic properties of thin films and solutions are observed. This is consistent with the absence of interactions between polymer side chains. The absorption and fluorescence spectra of PSt-NI studied in various solvents of different polarity are compared to the corresponding spectra of NI. The longest wavelength absorption of PSt-NI and NI is characterized by a band with a maximum wavelength around 410 nm. The peak position is sensitive to the polarity of the solvent, which is in agreement with the charge transfer character of the transition. The fluorescence spectrum of PSt-NI shows a maximum emission in chloroform at 515 nm and is red shifted compared to those of NI. Fluorescence lifetimes of PSt-NI and NI are measured in presence and absence of 2,4-dinitrotoluene (DNT) and the results are interpreted via the Stern-Volmer analysis. In solution, the fluorescence quenching of NI is purely collisional, whereas both dynamic and static quenching are observed with PSt-NI Upon 1 minute exposure to DNT vapor, it was shown that a 5 nm thick film of PSt-NI exhibited a 45% drop in its fluorescence intensity, which makes this polymer very attractive for sensing applications.
Highly efficient blue and white light-emitting organic electroluminescent devices have been fabricated by evaporation of small molecules. The emitting material of the blue multilayer EL devices (ITO/CuPc/α-NPB/Doped DPVBi/Alq3/LiF/Al) is based on a DPVBi (4,4'-bis(2,2-diphenylvinyl)biphenyl) matrix. In order to increase the EL efficiency and to improve the blue colour, this emitting layer is doped with a derivative of distyryl biphenyl molecules: PR3491. After the optimisation of the percentage of dopant, quantum and current efficiencies of 5.7 % and 7 cd/A, respectively, are obtained for a deep blue diode with CIE chromaticity coordinates of (0.15, 0.14). White diodes have been also realized doping the DPVBi emitter or the α-NPB hole transporting layer (HTL) of the previous structure with rubrene. A double doped system has been finally realized from the deep blue diode (DPVBi doped with PR3491) and with rubrene in the HTL layer. After tuning the two percentages of dopant in order to balance the blue and the yellow contribution to the diode emission, a fairly pure white emission is obtained with CIE coordinates of (0.31, 0.34) and external efficiencies of 3.4 % and 8.7 cd/A at 10 mA/cm2.