Performance Study Of Polymer Solar Cells And Exploration Of Nano-imprinting Devices

There exist phase seperation ranges from nano to micro scale in bulk heterojunction of polymer solar cells (PSCs), which is unfavorable for exiton separation and charge transfer efficiency. The ideal active layer with interpenetrating structure can largely overcome many problems that traditional blend structure have and has gradually become a research focus in this field, attracting a lot of research at home and abroad. Nanoimprint lithography is a simple and feasible method to control the morphology of active layer and realize the ideal double layer interpenetrating structure. This technology can not only adjust the interface area of donor/accepter through the change of nano template size, but also improve the hole mobility result from the polymer molecular orientation change during the nanoimprint. Double-imprint technique has achieved great research results in building ideal interpenetrating structure, but the shortcoming need to be further improved. The ultimate aim of this thesis is to build high-performance PSCs with nano interpenetrating network structure, around this aim, a series of work has been done. Main contents were as follows:(1) Nano-imprinting is usually carried out in air. In order to build high-performance PSCs with nano interpenetrating network structure, the materials that are sensitive to air and disadvantage for device stability should be largely avoided. The optimization of interface and device structure were conducted based on blend Bulk heterojunction active layer. As a substitution of low work function metal, a novel conjugated polyelectrolyte were successfully used as cathode buffer layer in PSCs. By investigating the influence of interface layer structure and thickness on the performance of photovoltaic devices, we concluded that PFEOSO3Na with PEO derivative side chain and anionic groups showed the best device performance. We conducted different annealing sequence on PFEOSO3Na layer, and AFM measurement indicated that the morphology of interface layers is largely dependent on annealing due to the incompatibility between the hydrophilic interface layer and hydrophobic active layer, resulting in the difference of device preformance. The successful application in PSCs based on low bandgap materials initially showed its universality. (2) In addition, the acidic hole transport layer PEDOT:PSS can corrode the surface of the ITO and affect the device lifetime. New inverted PSCs were fabricated by introducing an ultrathin aluminum interlayer modified aluminum-doped zinc oxide (AZO) electrode as the bottom electrode. Through the optimization of pretreatment and thicknesses of ultrathin aluminum, the power conversion efficiency can reach to3.84%. The surface pontential measurements demonstrated the significant decrease of AZO workfunction among the deposition of ultrathin aluminum. The comparison between the devices with different structure based on P3HT:ICBA active layer further presented its broad application prospect.(3) PSCs with ideal double layer interpenetrating active structure is developed from the bilayer devices, it is essential to optimize the bilayer reference devices. The peformance optimization of bilayer planar devices were conducted based on P3HT/PCBM. By adjusting the thickness of P3HT, PCBM and the annealing temperature, the power conversion efficiency of P3HT/PCBM planar devices can achieve2.7%. The influence of methanol additive on the hole mobility and device performance of bilayer devices were also investigated.(4) Based on micro-nano processing technology, the preparation technology of nano-imprinting template were explored and optimized. Through the process optimization, including exposure dose and etching process, etc, both of the direct method and metal transfer method can achieve nanostructure array with large area and hyperfine small size. The minimum diameter of cylinder arrays is20nm, with a period of50nm, which is in the leading domestic level. The optimized process has guiding significance for the preparation of micro-nano structure.(5) The precondition of fabricating bilayer interpenetrating active structure using double imprint technology is to build nanostructure arrays of donor or accpter. In order to form an anti-sticking layer, the surface of silicon mold was modified with fluoroalkyl silanes. Additionaly, in order to avoid the pollution and damage of the pristine mold during the nanoimprint process, the ormostamp was used for the replication of silicon mold. The hard ormostamp template with highly uniform nanostructure can be obtained among the process optimization. Based on the thermal printing technology, the effect of imprint temperature and pressure on nanostructure was investigated, finally the nanostructure arrays of P3HT, PCBM and ICBA were obtained with a period of100nm and a diameter or linewidth of50nm.