A novel RGB color patterning method for the fabrication of AMOLEDs was demonstrated on a lab scale in this work. Jouleheating Induced Color Patterning (JICP) is a high resolution patterning process where sublimation of small organic molecules is induced by applying electric pulse to a pre‐patterned conductive layer on a donor glass. It was found that the JICP process has a potential for high resolution patterning of >700 ppi and for patterning large‐sized panels such as Gen. 8 glass substrate.

We demonstrate a high efficiency organic tandem cell based on a pair of sub-cells employing solution and vapor deposited donors and a fullerene acceptor. One sub-cell that absorbs primarily from the green into the near infrared consists of a solution-processed, solvent-vapor-annealed blended squaraine/C70 bilayer heterojunction, while the second, visible absorbing sub-cell consists of a vapor-deposited tetraphenyldibenzoperiflanthene (DBP):C70 planar-mixed heterojunction. The resulting stacked tandem device harvests photons of λ <; 800 nm while providing an open-circuit voltage (VOC) of 1.83 V and ηp = 7.8 ± 0.4 %.

We describe a hybrid planar-mixed heterojunction (PM-HJ) organic photovoltaic cell based on tetraphenyldibenzoperiflanthene (DBP) and C70 with a power conversion efficiency of up to 6.4% ± 0.3%. Optimized cells consist of a DBP:C70 mixed layer at a volume ratio of 1:8 and a 9-nm thick C70 cap layer. The external quantum efficiency (EQE) in the visible of the PM-HJ cell is up to 10% larger than the mixed-HJ cell that lacks a C70 acceptor cap layer. The improvement in EQE is attributed to reduced exciton quenching at the MoO3 anode buffer layer surface. This leads to an internal quantum efficiency >90% between the wavelengths of λ = 450 nm and 550 nm, suggesting efficient exciton dissociation and carrier extraction in the PM-HJ cell. The power conversion efficiency under simulated AM 1.5G, 1 sun irradiation increases from 5.7% ± 0.2% for the mixed-HJ cell to 6.4% ± 0.3% for the PM-HJ cell, with a short-current density of 12.3 ± 0.3 mA/cm2, open circuit voltage of 0.91 ± 0.01 V, and fill factor of 0.56 ± 0.01.

It has been proposed that interface morphology affects the recombination rate for electrons and holes at donor-acceptor heterojunctions in thin film organic photovoltaic cells. The optimal morphology is one where there is disorder at the heterointerface and order in the bulk of the thin films, maximizing both the short circuit current and open circuit voltage. We show that an amorphous, buried functionalized molecular squaraine donor layer can undergo an "inverted" quasi-epitaxial growth during postdeposition processing, whereby crystallization is seeded by a subsequently deposited self-assembled nanocrystalline acceptor C60 cap layer. We call this apparently unprecedented growth process from a buried interface "inverse quasi-epitaxy" where the crystallites of these "soft" van der Waals bonded materials are only approximately aligned to those of the cap. The resulting crystalline interface hastens charge recombination, thereby reducing the open circuit voltage in an organic photovoltaic cell. The lattice registration also facilitates interdiffusion of the squaraine donor and C60 acceptor, which dramatically improves the short circuit current. By controlling the extent to which this crystallization occurs, the voltage losses can be minimized, resulting in power conversion efficiencies of ηP = 5.4 ± 0.3% for single-junction and ηP = 8.3 ± 0.4% for tandem small-molecule photovoltaics. This is a general phenomenon with implications for all organic donor-acceptor junctions. That is, epitaxial relationships typically result in a reduction in open circuit voltage that must be avoided in both bilayer and bulk heterojunction organic photovoltaic cells.

We develop a partially solution-processed small molecule tandem organic photovoltaic cell using an organic/inorganic interlayer structure that provides efficient charge recombination while protecting underlying layers from degradation due to attack from solvents applied during the deposition of subsequent sub-cells. Each sub-cell consists of a functionalized squaraine (fSQ) blend donor that is cast from solution, followed by evaporation of other functional layers. The first fSQ layer is cast from chloroform, while the second is cast from a tetrahydrofuran, thereby minimizing dissolution of the relatively insoluble, underlying fullerene layer that acts to protect the first donor layer. Solvent vapor annealing increases the sub-cell performance while decreasing the damage caused by spin-coating of the second fSQ layer, both of which result from increased film crystallinity that reduces the rate of solvent penetration. The tandem cell has a power conversion efficiency of 6.2% ± 0.3% and an open circuit voltage nearly equal to the sum of the constituent sub-cells.

We develop a framework to understand the performance of tandem organic photovoltaic (OPV) cells consisting of a series-connected stack of an arbitrary number of sub-cells. The power conversion efficiency penalty, Δη, is defined as the loss incurred when the tandem cell is at its maximum power point (MPP) but one or more sub-cells are not operating at their individual MPPs. To minimize Δη, the current at the MPP for each sub-cell must be equal. We also develop a method to calculate the tandem cell spectral mismatch factor and fill factor, showing that they are related to both the fill factors and short circuit currents of all the constituent sub-cells. By including the current generated in the dark, exciton dissociation at the donor-acceptor heterojunction, and photoconductivity, along with current losses due to polaron-pair and bimolecular recombination, we simulate the operation of small molecule bilayer and mixed-layer sub-cells used in the tandem, and from these results derive the behavior of the integrated device. This analysis is used to understand and optimize tandem OPV cell performance.

We demonstrate the concentration dependence of C60 absorption in solid solutions of C60 and bathocuprione (BCP), revealing a nonlinear decrease of the C60 charge transfer (CT) state absorption. These blends are utilized to study the photocurrent contribution of the CT in bilayer organic photovoltaics (OPVs); 1:1 blends produce 40% less photocurrent. As exciton blocking electron transporting layers, the blends achieve power conversion efficiencies of 5.3%, an increase of 10% compared to conventional buffers.

We demonstrate a tandem organic photovoltaic cell incorporating solution- and vacuum-deposited small molecules as the active layers. A blue and green-absorbing boron subphthalocyanine chloride:C-70 graded heterojunction (HJ) sub-cell is combined with a green and red-absorbing functionalized squaraine/C-70 bilayer HJ sub-cell, resulting in a tandem cell with a wavelength response from 350 nm to 800 nm. The efficiency of the cells depends on process conditions such as solvent annealing, resulting in nanocrystalline morphology that leads to improved charge and exciton transport compared with un-annealed cells. The incorporation of C-70 in both sub-cells leads to an increase of short-circuit current by at least 30% compared to analogous cells using C-60. The optimized power conversion efficiency of the tandem cell is 6.6% +/- 0.1%, with an open-circuit voltage of 1.97 +/- 0.1 V under simulated 1 sun, AM 1.5G illumination. The tandem cell voltage is equal to the sum of the constituent sub-cells, indicating that the transparent, Ag nanoparticle/MoO3 compound charge recombination layer interposed between the cells is nearly lossless. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.4742921]