Regulation And Optimization Of Organc/Inorganic Interface In Polymer Solar Cells

Due to its low cost, flexibility, transparency, easy manufacturing and up-scaling, etc., polymer solar cells have attracted considerable attentions. Extensive efforts have been directed at developing polymer solar cells with high-efficiency, such as molecular design and optimized morphology of active layer, and interfacial modifications. New molecular structure of active layer materials was designed to maximize the sunlight absorption. The donor/acceptor interface of active layer was optimized to improve the charge generation and transmission. The interface between active layer and electrode was modified to improve the charge collection at corresponding electrode.Due to the insolubility between organic and inorganic phases, the morphology of quantum dots in hybrid solar cells could be regulated by the following methods: functionalized block copolymers, interfacial compatibilizer of block copolymer, in-situ grown in ordered polymer matrix and cooperative self-assembly of liquid crystalline. The dispersion and assembly of quantum dots were driven by the self-assembly of block polymers. Rod-coil block polymer P3HT-b-PEO was synthesized as the electron donor to induce the dispersion of electron acceptor ZnO, due to the interaction between the oxygen atoms of PEO chains and the polar surface of ZnO group. Then the photovoltaic performace of cells based on P3HT-b-PEO/ZnO was increased, compared to pristine cells with P3HT/ZnO. Considering the none-conjugated feature of PEO block, the photovoltaic performace of P3HT/ZnO hybrid solar cells was improved via P3HT-b-PEO as the interfacial compatibilizer. Because the phase separation size between organic P3 HT and inorganic Zn O could be optimized by the small amount of P3HT-b-PEO. To further improve the phovoltaic properties, a rod-rod block copolymer with liquid crystalline side chain, P3HT-b-PTcbp was synthesized as the electron donor. Inorganic nanocrystals containing the ligand with same mesogenic were provided as electron acceptor in the hybrid active layer. Due to the co-assembly of the side chain liquid crystalline of rod-rod block copolymer and mesogenic ligands of inorganic crystals, the hybrid system can be driven to assemble into well orderly nano-morphology. Besides, we also used amphiphilic rod-rod block copolymer P3HT-b-P3 TEGT as the matrix to in-situ synthesis of inorganic nanocrystals CdS. The oxygen side chain of P3 TEGT section made the block copolymer soluble in polar solvent such as MeOH, the nanostructure of P3HT-b-P3 TEGT can be controlled by the mixed solvents of methanol and cholobenzene. Originiating from the solubility of CdS precursor in methanol only and the coordinated interaction between Cd2+ and the oxygen of side chain of P3 TEGT segment, the in-situ formation of CdS should be generated in the P3 TEGT segment. Driving by the crystallinity of the block copolymer backbone and the directional distribution of CdS in P3 TEGT segment, the one-dimensional donor/acceptor core/shell hybrid nanobeams network was finally obtained. These more ordered nano-morphology can improve the efficiency and stability of the cells.For the interfacial modification, P3HT-b-P3 TEGT containing ethyleneoxide side chains was added into active layer P3HT:PC61BM. During the spin-coating process of active layer solution, the triethylene glycol side chains of P3HT-b-P3 TEGT could spontaneously migrate vertically towards the active layer surface and form a nanoscale self-assembled buffer layer. The interface layer can improve the interfacial ohmic contact between organic active layer and inorganic electrode. The efficiency of the cell was increased to 4.2%. The well-aligned and highly uniform one-dimensional ZnO nanoarrays were synthesized through hydrothermal synthesis as the electron transport layer of invered devices. Length of the ZnO nanoarrays could be controlled by the concentration of ZnO seeds and hydrothermal growth time. The ZnO nanoarrays were formed due to its more conducive for the electron transport and collection. The surface of the ZnO nanoarrays was further modified by the small molecules, such as organic dye and liquid crystals, which were benefit for reducing the defects of Zn O nanoarrays surface. Finally, the power conversion efficiency of device was increased to 8%.In addition, the common material in the interlayer is the conjugated polyelectrolytes. The conjugated polyelectrolyte with electron deficient backbone is less studied, mainly due to its challenge in synthesis. We have synthesized CPEs with poly-benzotriazole conjugated backbones, but different side chains via Yamamoto coupling polymerization directly from the ionic monomers. The optical properties of this series of polymers were investigated. Different ionic side chains(pyridinium, tetraalkylammonium vs. sulfonate-terminated) impact how the materials aggregate in solutions, as observed in absorption and DLS measurements. CPEs with tetraalkylammonium side chains exhibit the most red-shifted absorption maxima, the largest aggregate size, and the highest fluorescence quantum yield(up to 61% in MeOH). The optical properties of these CPEs can also be tuned by the choice of solvents. Negative solvatochromic effects are observed for both cationic CPEs. These studies provide insights into the role of structural modification of pendant ionic functionalities on the optoelectronic properties of the CPEs. These CPEs provide a class of novel materials for future applications in optoelectronic devices.