Fabrication And Photoelectrical Properties Of Small-Molecule Organic Semiconductor Films

Derivatives of phthalocyanine (Pc) and perylene diimide (PDI) as excellent organic semiconductors, have been studied extensively in the organic photoelectric devices. But there still are some obstacles to their applications, such as low solubility, lack of simple and controllable film formation method, and immature theory of the photoelectrical transformation. In this dissertation, the research progresses on these organic semiconductors are summarized firstly. On the base of these, the film formation methods to them and the photoelectrical properties of their films are studied as follows:(1) The electron donor-acceptor (D-A) molecules, 4,7-bis(4-triphenylamino)benzo- 2,1,3-thiadiazole (TBT), is synthesized via Stille cross-coupling reaction. And the nanocrystalline films of TBT have been firstly formed by a facile protonation- electrodeposition (PED) method from the nitromethane solution of protonated TBT, in which trifluoroacetic acid (TFA) is used as the protonation reagents. The films are composed of nanospheres which diameters are controllable from 20 to 200 nm. Compared with the spin-coating films, PED films possess higher degree crystallization and lower band gap, with respect to superior intermolecular charge-transfer ability and more excellent hole-transporting property.(2) Films composed of various nanostructured copper phthalocyanine (CuPc) are controllably prepared by the method of PED, under the low voltage and the small molar ratio of TFA to CuPc. The ultralong nanowires of CuPc are grown at a high deposition temperature of 70?.(3) The composite films of TBT:CuPc are fabricated via protonation-coelectro- deposition (PCD) from the nitromethane solutions of the TBT:CuPc mixture in the presence of TFA. The crystallization behavior of the two components is interacted by each other. Furthermore, the morphology of the composite films are controlled by relative content and codeposition time. The nanosphere-nanowire interpenetrating network structured films are obtained when the molar percentage of TBT being 70% in the precursor solutions. Based on the absorption and emission spectra as well as the match of molecular energy, there theoretically exists energy/charge transfer at the interface of TBT/CuPc heterojunctions. And the deduction of the charge transfer is proven by the obvious enhanced effect of the surface photovoltage (SPV) in the composite films which codeposited from the TBT:CuPc blending solutions of 50% and 70%TBT, respectively.(4) The reduction reactions of the two PDI derivatives, N,N'-di(4-methoxybenzyl)- 3,4,9,10-perylene diimide (PDI-32) and N,N'-di(4-ethoxyphenyl)-3,4,9,10-perylene diimide (PDI-123), with hydrazine hydrate (HZH), are thoroughly studied in the DMF solutions, respectively. On the base of this, the single-component and blending composite films of the two PDI are fabricated from the anionic radicals-contained solutions via anionic radical-electrodeposition (AED) and anionic radical-coelectrodeposition (ACD), respectively. The morphology of the AED films is controlled by the dissolving of PDI followed with the reduction reactions. And the dissolving is not only influenced by the content of HZH, but also dependent on the storing time. The surface photovoltage spectra (SPS) of the two single-component films indicate that, PDI-123 film composed of nanoparticles present stronger photovoltage response than the nanobelt/rod-composed PDI-32 films, due to the surface states and absorption of O2 on the PDI-123 nanoparticels. The SPS of the PDI-32:PDI-123 composite films show the SPV enhanced effect at the two absorption bands of 600~700 nm and 330~425 nm, respectively. And the former one is ascribed to the surface states and absorption of O2 on the PDI-123 nanoparticles, which make the photoinduced excitons in the neighbouring PDI-32 molecules be dissociated effectively, the later one is attributed to the coactions of the mentioned surface effect and the intermolecular charge transfer on the PDI-32/PDI-123 interface.(5) Based on the film formation methods of PED and AED, the p/n-type double-layer heterojunction composite films of TBT/PDI-32, TBT/PDI-123, CuPc/PDI-32, CuPc/PDI- 123,TBT:CuPc/PDI-32 and CuPc/PDI-32:PDI-123, are fabricated by means of layer-by- layer electrodeposition. The SPV enhanced effect presented in these double-layer films indicates that there exist the photoinduced intermolecular charge transfer at the heterojunction interface. And also, this charge transfer possesses different influence on the different type of exciton dissociation, which induces the complementarity of the SPV enhanced effect among various films. In addition, the double-layer films containing the bulk blending layer, not only show the interface effect in the simple double systems, but also present the photovoltage enhancement in the bulk composite films.This dissertation provides the flexible and controllable film formation methods for the derivatives of TPA, Pc and PDI, and obtained their composite films with SPV enhanced effect. Meanwhile, the dissociation mechanism of the different type of photoinduced exciton in the films is studied by SPV technology. This work provides abundant experiment data which will be significant for the fabrication of photoelectrical devices based on these derivatives.