Synthesis of quantum dots, PUA polymer and its application in organic

Abstract

The organic, perovskite photovoltaics show tremendous device performance in recent researches and considers as the emerging photovoltaics in industrial fields due to the low fabrication cost and mechanical flexibility. However, as the organic, perovskite photovoltaic shows relatively low device performance and poor device stability, improving device stability and efficiency is a main issue to commercialize this photovoltaics. In this dissertation, the more effective photovoltaic devices were fabricated by modifying device interlayer and fabrication process. In chapter 2, this research focuses on the effect of ligand exchanged CdSe quantum dots (QDs) interlayer to solve the self-aggregation, and applied to uniform coating of QDs in inverted organic solar cells. Because the oleic acid ligand has a tendency to act as an insulator, the ligand exchange of CdSe has been reacted from an oleic acid ligand to pyridine to increase conductivity. To overcome the general problems of self-aggregation of ligand exchanged inorganic nanoparticles, we carried out a chemical treatment using by a 3-mercaptopropionic acid (3-MPA) on top of ZnO layer for grafting CdSe QDs which give rise to the uniform formation of CdSe QDs layer between ZnO and active layer. The ligand exchanged CdSe QDs layer contributed to the increased device efficiency over 5% in the inverted organic solar cells due to the role of electron transport and hole blocking effects, which correlated to the enhanced FF from decreased series and increased shunt resistance compared to the device without interlayer. In chapter 3, we investigates non-FOTS based PUA stamping transfer and the different surface energy properties that result in various physical phenomena when used for organic photovoltaics. To transfer the material, the energy release rate (G) between the PUA and the coated material should be smaller than the G between the coated material and the substrate. As a result, hydrophilic PUA was used to reduce the interaction between the PUA and the organic bulk heterojunction (BHJ) layer to transfer the BHJ layer from the PUA stamp to a PEDOT:PSS coated ITO-substrate. 2-Hydroxyethyl methacrylate (HEMA) is included as the reactive diluent to reduce the PUA viscosity, and the contact angle was measured to compare the surface property between the reference PUA and the HEMA-PUA. The stamping-transferred BHJ device exhibits a 95% relative efficiency (2.9%) when compared to that obtained when using a spin-coating process, which is considered as a good alternative to fabricate optoelectronic devices. More importantly, we have found a decrease in the fill factor (64 to 58%) and a comparable performance (3.0% to 2.9%) derived from the increase in the charge recombination and resistance during the stamping transfer. In chapter 4, we fabricated low temperature based inverted semitransparent CH3NH3PbI3 perovskite photovoltaics. The work function of PEDOT:PSS (PH 1000) electrode was modified using polyethylenimine (PEI) and both layers are transferred on the $ITO/PEDOT:PSS/CH_3NH_3PbI_3/PCBM$ layer using hydrophobic polyurethane acrylate (PUA) polymer stamp. Even if the PH 1000 spin coating on the $CH_3NH_3PbI_3/PCBM$ layer shows degradation of perovskite due to the inter-diffusion of PH 1000 solvent, drying transfer shows effective layer stacking without degradation. The PEI treatment on the PH 1000 contributes to reduce the work function from 5.1eV to 3.97eV and this modification makes to improve the device performance from 0.07% to 4.02%. The full device average visible transmittance (AVT) exhibits 24.58% and the work function modification shows the decreased charge transporting resistance (Rc), which directly correlate to the enhanced open circuit voltage (Voc) short circuit current (Jsc) and fill factor (FF).