Study Of Interface Influence On Active Layer And Electrode For Organic Photovoltaic Cells

In this paper, we designed and synthesized a series of small molecular donormaterials, fullerene derivative (13F-PC61BM) acceptor containing fluorocarbonmoiety and a series of graphene oxide with precise oxidation. Through deliberatelycharacterization of materials’ intrinsic properties, the interface between donor andacceptor, electrode and active layer, some important contents and discussions are asfollows:1. A series of Acceptor-Donor-Acceptor (A-D-A) based small moleculescontaining DPP groups with varied crystallinity (T(TDPPT)2, TT(TDPPT)2andBDT(TDPPT)2) was designed. Through theoretical calculation, those small moleculeshave different coplanar properties, showing varied crystallinities. The processing DIOcan induce the SMs to form higher nanoscale crystallinity and controllable scales ofnanofibrils. The self-organized ordered smaller nanofibrils varied from4nm,10–15nm to15–20nm. Besides, through hole mobility and electron mobility test of SMs:PC71BM blend films, that more balanced hole mobility and electron mobility arebenefit to the improvement of device fill factor and efficiency.2. A new kind of fullerene derivative (13F-PC61BM) containing fluorocarbonmoiety was designed and synthesized. The proper molecular design of introducingbulk fluorocarbon chain can provide a free region and effectively inducepoly(3-hexylthiophene)(P3HT) to self-organize into P3HT crystallites. In the absenceof any external treatment, optimal active layer morphology with long range order,nanoscale phase separation and bi-continuous transportation channels was achieved.Compared with P3HT: PC61BM system, the photovoltaic device based on P3HT:13F-PC61BM exhibited excellent performance without any post-treatment. But due tofluorocarbon moiety has stronger rigidity, which would hinder the movement of P3HTsegment, device with P3HT:13F-PC61BM did not show better efficiency comparedwith P3HT: PCBB-C8which was reported by our group before.3. A simple method for synthesizing a series of graphene oxide with preciseoxidation (pr-GO)(mild oxidation, moderate oxidation and severe oxidation) bystrictly controlling pre-oxidation steps, oxidant content and oxidation time has been successfully developed. pr-GOs present multiple functionalities, like modulation ofwork function, enhanced interfacial dipole, and excellent film-forming properties, tobe an excellent hole extraction material to improve efficiency and stability of organicsolar cells. The P3HT: PCBM system device based on pr-GOs hole extraction layer(HEL) with well defined electronic structure and moderate oxidation exhibited betterpower conversion efficiency and air-stability compared to the devices with otherpr-GOs and conventional PEDOT:PSS interfacial layer. In this part of work, weconclude that electrode interface engineering can be optimized by HEL structuresdesign.