Inkjet printing is considered a promising technique for industrial production of Organic Photovoltaic (OPV) devices,
especially due to its minimal consumption of materials, the easy modification of the numerical design and because this is
a non-contact process. The objective of this study is to make efficient modules at a semi-industrial scale using 128 nozzle
heads.
In order to maximize the performance and lifetime, an inverted device structure was used consisting of: transparent
plastic conductive substrate / N-layer / active layer / P-layer / silver electrode. Formulations and processes were therefore
developed for substituting each spin-coated layer with an ink-jet printed layer. For 3.7 cm2 cells power conversion
efficiency (PCE) reaches 3.3 % with only N-layer printed, 2.4 % with only active layer printed, 3.0 % with only P-layer
printed and 2.9 % with only the silver electrode printed.
Three-cell modules of 11 cm2 on 5x5 cm2 substrates were also made. Most PCE reach >2 % for each inkjet printed layer.
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.
Among the class of conjugated polymers, polythiophenes and in particular 3-alkyl-substituted thiophenes seem to focus all the attention in the domain of photovoltaic conversion. At CEA, we are working on the optimization of bulk heterojunction solar cells made of poly-3-hexylthiophene (P3HT)and [6,6]-phenyl C61 butyric acid methylester (PCBM) blend. First we will describe the influence of the ratio of P3HT and PCBM blend on the efficiency of the resulting bulk heterojunction solar cells. Best cells based on 1:1 in weight ratio yield 3.6 % power conversion efficiency under air-mass 1.5, 100 mW/cm2 illumination. Then we will compare the efficiency and lifetime of different cells by changing the nature and thickness of cathode (Aluminum or Calcium/Silver). On the optimized cells, we have proceeded to ageing and accelerated lifetime measurements on devices with Ca/Ag cathode. It shows that the current densities decrease less than 3 % and that efficiency is still higher than 1.7 %, after 400 hours under AM 1.5, 100 mW/cm2 illuminations and at high temperature (60°C).
Though being much less efficient than silicon cells, organic solar cells exhibit a unique combination of interesting properties: low cost, flexibility, and the possibility of large surface coverage. Large progresses have been made over the last years using MDMO-PPV (Poly[2-methoxy-5-(3’,7’-dimethyloctyloxy)-1,4-phenylenevinylene) reaching efficiencies of 2.9% and recently efficiencies over 3%, using poly(3-hexyl thiophene). A great deal of research however has still to be invested to improve the current state of the art. Among the main key-points to be addressed are namely the stability and lifetime of such devices.
We are currently working on bulk heterojunction solar cells made from MDMO-PPV and PCBM (methano-fullerene[6,6]-phenyl C61-butyric acid methyl ester). Different batches of MDMO-PPV, originating from different synthesis modes (classical "Gilch" synthesis and "Sulphinyl" synthesis led by IMEC-IMOMEC) have been tested. Evolution of the power efficiency following continuous illumination (AM1.5, 80 mW.cm-2) was characterized under controlled atmosphere of nitrogen. In parallel, photodegradation studies are also investigated and electrical modeling is under way in order to get a better understanding of the relations between photochemical and electrical parameters of the diode that can be deduced from I/V curves.
Though being much less efficient than silicon cells, organic solar cells exhibit a unique combination of interesting properties: low cost, flexibility, and the possibility of large surface coverage. Large progresses have been made over the last years using MDMO-PPV (Poly[2-methoxy-5-(3’,7’-dimethyloctyloxy)-1,4-phenylenevinylene) reaching efficiencies of 2.9% and recently efficiencies over 3%, using poly(3-hexyl thiophene). A great deal of research however has still to be invested to improve the current state of the art. Among the main key-points to be addressed are namely the stability and lifetime of such devices.
We are currently working on bulk heterojunction solar cells made from MDMO-PPV and PCBM (methano-fullerene[6,6]-phenyl C61-butyric acid methyl ester). Different batches of MDMO-PPV, originating from different synthesis modes (classical "Gilch" synthesis and "Sulphinyl" synthesis led by IMEC-IMOMEC) have been tested. Evolution of the power efficiency following continuous illumination (AM1.5, 80 mW.cm-2) was characterized under controlled atmosphere of nitrogen. In parallel, photodegradation studies are also investigated and electrical modeling is under way in order to get a better understanding of the relations between photochemical and electrical parameters of the diode that can be deduced from I/V curves.
Organic solar cells based on interpenetrated network of conjugated polymer as donor and fullerene derivative as acceptor materials have a great potential for improvement of the efficiency. We fabricated a device based on a composite of poly(2-methoxy-5-(2'-ethylhexyloxy)-1,4-phenylenevinylene (MEH-PPV) and [6,6]-phenyl C60 butyric acid methyl ester (PCBM). Surface treatment, insertion of interfacial layers, and improvement of the morphology of the active layer significantly increase the photovoltaic performances of the structure. We obtained an open circuit voltage of 0.87 V and short circuit current density of -8.4 mA/cm2 under 100 mW/cm2 AM 1.5 solar simulator illumination, yielding a 2.9 % power conversion efficiency. Two others fullerene derivatives were synthesized in order to get a stronger acceptor. The electrical and optical properties of devices made with MEH-PPV and these acceptors are investigated.
The nonvolatile transistor memory element is an interesting topic in organic electronics. In this case a memory cell consists of only one device where the stored information is written as a gate insulator polarization by a gate voltage pulse and read by the channel conductance control with channel voltage pulse without destruction of the stored information. Therefore such transistor could be the base of non-volatile non-destructively readable computer memory of extremely high density. Also devices with polarizable gate dielectrics can function more effectively in certain circuits. The effective threshold voltage Vt can be brought very close to zero, for applications where the available gate voltage is limited. Resonant and adaptive circuits can be tuned insitu by polarizing the gates. Poly(vinylidene fluoride), PVDF and its copolymer with trifluoroethylene P(VDF-TrFE) are among the best known and most widely used ferroelectric polymers. In this manuscript, we report new results of an organic FET, fabricated with pentacene as the active material and P(VDF-TrFE) as the gate insulator. Application of a writing voltage of -50 V for short duration results in significant change in the threshold voltage and remarkable increase in the drain current. The memory effect is retained over a period of 20 hours.
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