Study On Well-ordered Structure Materials, Interfaces And Performances Of Organic-based Solar Cells

Increasing the mobility of organic materials, optimizing the thin-film device interface and designing device structure are the three key factors which affect heavily the performance of organic solar cells. In this dissertation, we carried out research work on organic solar cells based on the mentioned three aspects.Organic-inorganic hybrid perovskites combine useful attributes of organic and inorganic components within a single molecule, which provides interesting optical, electronic and magnetic properties. It demonstrates a promising application prospect in optoelectronic device field, such as light emitting diodes and thin film field-effect transistors. Thus the hybrid perovskite materials have recently received substantial attention. However, study on well-ordered perovskite materials applied in solar cells has not been reported yet.Three typical well-ordered organic-inorganic hybrid perovskites were synthesized. The structure, UV-Vis absorption, crystallinity, stability and charge transport performance of (NH3C6H4OC6H4NH3)PbI4, (C14H13N2O2)2PbCl4 and (3-BrC3H6NH3)2CuBr4 have been investigated. The results show that organic-inorganic hybrid perovskites possess of excellent photoelectric properties. (NH3C6H4OC6H4NH3)PbI4 demonstrates a room-temperature electron mobility of 0.065 cm2·V-1·s-1. (C14H13N2O2)2PbCl4 is well-ordered, and has good photovoltaic response and extraordinary photoacoustic characteristics under UV light exposure. (3-BrC3H6NH3)2CuBr4, which exhibits prime absorptive character in the UV-Vis spectral, high mobility as well as two-dimensional layered well-ordered crystal structure could be used in organic-based solar cells.Interface issues such as surface contact and the defects would affect the performance of the thin-film optoelectronic devices at a large extent. In order to further study materials interaction and aggregation state structure which provides a theoretical basis for optimization of device performance, the CuPc/Au/C6o structure prototype is designed and fabricated. CuPc/C6o structure heterojunction is also designed as a control. UPS, XPS and other characterization methods are used to study the organic/metal interface. The aggregation structure of the device and the formation of metal/organic surface and interface are also investigated, and the energy level structure of CuPc/Au/C6o heterojunction is obtained. The results show that the polarization of Au forms dipole between organic material and Au. The XPS spectra of Cu3d and NlS indicated that the band bending occurrs between the two materials. So the changes of surface work function are due to the band bending and the interface dipole co-effect. Furthermore, CuPc/DFPP heterojunction with organic/organic contacting interface has also been designed and studied by photoelectron spectroscopy. The energy level structures of the materials around the interface are also obtained. A strong charge transfer occurrs in the heterojuction, demonstrating a promising application prospect in optoelectronic device fieldA new n-type material 5FAlq3 was synthesized. The interface structures and the level structures between 5FAlq3 and Ag have not been reported yet. The interfaces of 5FAlq3 deposited on Ag and Ag deposited on 5FAlq3 were investigated respectively. We conclude that binding energy shifts are consistent with the formation of a polarized molecular layer, or interface dipole, and thus are inconsistent with an electrostatic band-bending model.At last, p-type well-ordered perovskite was introduced into solar cells for the first time. The perovskite not only has a good spectral response in the UV-Vis range but also has good complementarity with C60. Therefore, spin-coating and vacuum deposition were used to fabricate solar cell prototype based on ITO/(3-BrC3H6NH3)2CuBr4/C6o/Al structure in order to take advantage of low-cost, easy-processing and high mobility of organic-inorganic hybrid perovskite materials. Charge transport and photovoltaic performance of this layered heterojunction was studied. The influence of annealing temperature and the film morphology on the performance of the device was also investigated. The best Voc, Jsc, FF andηof the devices are obtained as 0.38 V,0.21 mA·cm-2,0.25 and 0.021% after the low temperature annealing treatment, which leads to an ordered organic array in the perovskite. The power conversion efficiency is 23 times higher than the device withnot annealing treatment.To investigate the surface plasmon-inhanced optical absorption and photocurrent in organic bulk heterojuction photovoltaic device, we designed ITO/PEDOT: PSS/CuPc/Au/CuPc/C6o/Al structure device. By adjusting the position of 1 nm thick Au layer in CuPc film, we found that when Au nanoparticles was in the middle of CuPc film,10 nm from the heterojunction interface, the device had the best performance because of exciton produced by plasmon-inhanced optical absorption could make effective transmission to CuPc/C6o heterojunction interface and effective separation. The distritubion of excition in CuPc layer was effectively changed, and the exciton density was enhanced by the Au nanoparticle surface plasmon resonance. The performance of the device increased 2.85 times than the device without Au nanoparticles.