Lizhen Huang

Efficient Organic Solar Cells Using a High-Quality Crystalline Thin Film as a Donor Layer

An efficient organic solar cell is fabricated by the weak-epitaxy-growth method and the achieved power conversion efficiency is over 3% (see figure). A Single-crystal-like thin film improves the carrier mobility and reduces the electron hole recombination. Deposition of a zinc phthalocyanine (ZnPc):C60 mixed layer at 100 degrees C results in a better interpenetrating interface and the device performance is improved.

A feasibly synthesized ladder-type conjugated molecule as the novel high mobility n-type organic semiconductor

Two ladder-type conjugated molecules, i.e., 2,2′-(2,7-dihexyl-4,9-dihydro-s-indaceno[1,2-b:5,6-b′]dithiophene-4,9-diylidene) dimalononitrile (1) and 2,7-dihexyl-4,9-dihydro-s-indaceno[1,2-b:5,6-b′]dithiophene-4,9-dione (2) were synthesized in high yields, and their electrochemical properties, single crystal structures, thin-film morphology and field-effect mobility were investigated. The LUMO/HOMO levels of 1 and 2 are −4.07/−6.00 and −3.62/−5.82 eV, respectively, as estimated from the thin-film cyclic voltammetry measurements. In the single crystals, both compounds exhibit one dimensional π–π stacking of molecules, and 1 shows the larger π-electron overlap between the neighboring molecules than 2, along with interdigitation of alkyl chains. Thin-film X-ray diffraction (XRD) and atomic force microscopy (AFM) characterizations indicate that 1 can form films with higher molecular order than 2. Field-effect electron mobility up to 0.33 cm2 V−1 s−1 in air for 1 and hole mobility up to 0.05 cm2 V−1 s−1 for 2 have been demonstrated with the top-contact organic thin-film transistor (OTFT) device structure. Electron mobility of 1 is among the highest value for n-type organic semiconductors.

Tin (IV) phthalocyanine oxide : An air-stable semiconductor with high electron mobility

Air-stable n-type field effect transistors were fabricated with an axially oxygen substituted metal phthalocyanine, tin (IV) phthalocyanine oxide (SnOPc), as active layers. The SnOPc thin films showed highly crystallinity on modified dielectric layer, and the electron field-effect mobility reached 0.44cm2V−1s−1. After storage in air for 32days, the mobility and on/off ratio did not obviously change. The above results also indicated that it is an effective approach of seeking n-type semiconductor by incorporating the appropriate metal connected with electron-withdrawing group into π-π conjugated system.

Non-peripheral tetrahexyl-substituted vanadyl phthalocyanines with intermolecular cofacial π-π stacking for solution-processed organic field-effect transistors.

Four structural isomers of non-peripheral tetrahexyl-substituted vanadyl phthalocyanine can be easily separated using common laboratory column chromatography on a gram scale. The most abundant isomer, 1,8,18,22-tetrahexyl vanadyl phthalocyanine (I-3), adopts intermolecular 2D cofacial pi-pi stacking and exhibits a field-effect mobility of up to 0.13 cm(2) V(-1) s(-1).

Tunable Field‐Effect Mobility Utilizing Mixed Crystals of Organic Molecules

High-quality mixed crystals with mixing-ratio-dependent lattice parameters and electronic structure are obtained by co-deposition of two organic molecules. Using the mixed films as the inducing layer in weak epitaxy growth, the mobility of VOPc transistors is finely tuned. This is possible because of the cooperative effect between the tunable lattice parameters and electronic structure.

Crystalline organic superlattice

Highly crystalline organic superlattice has great potential for providing innovative function in organic devices. With studies of the structure and fundamental electronical properties, we have demonstrated the phathalocynine organic superlattice, which is a structure composed of periodically alternating crystalline layers of H2Pc and F16CuPc. A periodical crystal structure and electronic structure appear in this organic superlattice system. High density of mobile electrons and holes distribute periodically in F16CuPc and H2Pc layers, respectively, leading to a significant change in intrinsic properties of organic semiconductors.

Interfacial energy level bending in a crystalline p/p-type organic heterostructure

A conduction channel was observed at the heterointerface of the crystalline p-type organic films copper phthalocyanine (CuPc) and 2,5-bis(4-biphenylyl) bithiophene (BP2T). Energy level bending at the interface is confirmed by photoemission spectroscopy, which verifies a charge transfer between CuPc and BP2T. This provides a further route to utilize interfacial electronic properties in functional devices and also documents the importance of reconsidering the interfacial electronic structure of organic heterostructures.

Hole transparent and hole blocking transport in single-crystal-like organic heterojunction: when rods hold up disks.

Single-crystal-like organic heterojuntions are fabricated with disk-like molecules and different rodlike molecules. Hole transparent and blocking transport are demonstrated with photoemission spectroscopy and field-effect transistors. These results demonstrate a route to utilize adjustable interfacial electronic structure and control transport behavior in developing functional organic crystalline devices and crystalline nanocircuits.