Design,synthesis And Photovoltaic Properties Of A-D-A-Type Small Molecules Based On Porphyrin

With the growth of the population and the destruction of the ecological environment,the usage of solar energy has become an important research topic.Organic solar cells have the advantages of low-cost,flexible,potential of large-scale and semitransparent panels(such as spin coating,film coating,inkjet printing,etc.).This type of solar cells has power conversion efficiency more than 12%.However,to popularize the application of organic solar cells,power conversion efficiency and working life must be further improved.The main work of this thesis is design,synthesis and study of photovoltaic properties of A-D-A-type porphyrin based molecules for bulk heterojunction solar cells.This thesis systematically investigates how the substitution of some key atoms in the molecular structure,the substitution of electron withdrawing units,the optimization of side chains,the increase of π bridges and the expansion of conjugated systems would influence the energy levels,charge mobility and the performance of the photovoltaic device.With the design rules we got,we develop a small molecular material power conversion efficiency more than 9%.We believe that this thesis will provide guidance for the development of donor materials with high efficiency.In the second chapter,we designed and synthesized two small molecules PorODPP and PorSeDPP,with selenophene-terminated diketopyrrolopyrrole(DPP)or furan-terminated DPP units connected to porphyrin zinc core by ethynylene linkages,respectively.We tested the electrochemical properties,UV-Vis absorption spectra,photovoltaic properties,quantum chemical calculations,surface morphologies obtained by atomic force microscopy,UV-Vis absorption spectra and hole mobility of the active layer.The atom with larger the atomic weight can narrow the bandgap and broaden the absorption regularly.Contrasted with the thiophene analogue,selenophene and furan DPP can tune the bandgap and energy levels regularly.The PorSeDPP has better miscibility with PC61 BM and shows smaller phase separation in blend films.The devices based PorODPP and PorSe DPP have different mechanisms,and achieve optimized efficiency of 4.3 % and 5.8 % with pyridine and DIO as additives.In the third chapter,we designed and synthesized six small molecules with porphyrin zinc core and diketopyrrolopyrrole(DPP)unit.We select 1,3-di-tert-butylbenzene and bulky 5-(2-butyloctyl)benzo[b]thiophene as side chains of the porphyrin zinc core,respectively.Beside,we select 2-ethylhexyl chain,2-butyloctyl chain and 2-(2-(2-methoxyethoxy)ethoxy)ethyl chain as side chains of DPP unit.This chapter discusses how the side chains on the electron donor or the electron withdrawing units would influence the energy levels,charge mobility and the performance of the photovoltaic device.The molecules with benzothiophene group on porphyrin core have a deeper HOMO level.2-butyloctyl chain can reduce both LUMO and HOMO level,while the 2-(2-(2-methoxyethoxy)ethoxy)ethyl chain has the reverse effect.During the primary stage optimization,EHDPPEZnP-BzT reaches an efficiency of 6.8% with 1% pyridine as solvent additive,showing enormous potential.The other materials have poorer performance because of various shortboards.For EHDPPEZn P-BzT based devices,the fill factor and short current density of the solar cells increased significantly upon annealing by chloroform vapor,which was attributed to the preferable morphology and high mobility of the blend films.The PCEs kept above 95% upon chloroform vapor treatment within the range of 60 s to even 95 s,providing a wide processing window for reproducible fabrication.The photocurrent density versus effective voltage characteristics also proved that the solvent vapor annealing improved the exciton dissociation,charge transport and collection efficiency.The big sterically hindered benzothiophene groups on EHDPPEZnP-BzT reduced the HOMO level of the molecule,resulting in a higher VOC.The optimized BHJ devices exhibited an outstanding PCE of 9.08% with increased JSC and FF upon annealing by chloroform vapor for 80 s.In the fourth chapter,we designed and synthesized two novel small molecules with porphyrin zinc core and 5-heptyl-thieno[3,4-c]pyrrole-4,6-dione(TPD)unit: TPDTEZnP-BzT and TPDEZnP-Bz T.This chapter discuss the energy levels,charge mobility and the photovoltaic performance of the novel TPD-based materials and the effect of π-bridge in the molecules backbone.We test the electrochemical properties,UV-Vis absorption spectra,photovoltaic properties,UV-Vis absorption spectra and hole mobility.The Q band absorption in thin films of both molecules broadens and enhances greatly,with red-shift of 35 and 16 nm,respectively.TPDTEZnP-BzT with π-bridges shows narrower optical band gap and deeper HOMO level.0.4% chloronaphthalene as solvent additive and chloroform solvent annealing can improve their photovoltaic properties of device.For TPDTEZnP-Bz T:PC71BM based devices,with the increase of solvent annealing time,the open circuit voltage,short circuit current and filling factor all increase first and then decrease.A highest efficiency of 4.25% is achieved when the annealing time is 150 s.For TPDEZnP-BzT:PC71BM based devices,with the increase of solvent annealing time,the short-circuit current decreases and the filling factor increases first and then decreases.The highest efficiency reaches 4.82% when the annealing time is 150 sIn the fifth chapter,we designed and synthesized 3 novel small molecules with porphyrin zinc core and 1,1’-bis(2-ethylhexyl)-[3,3’-biindolinylidene]-2,2’-dione unit: PEEHID,PETEHID and PETEHIDT,and investigate how the thiophenes in the backbone influence the energy levels,charge mobility and the photovoltaic performance.We test the UV-Vis absorption spectra,electrochemical properties,quantum chemical calculations,photovoltaic properties and hole mobility of the active layer.The Q band absorption in thin films of all molecules broadens and enhances obviously with enormous red-shif.The more thiophenes in the backbone,the stronger the Q band absorption.PETEHID with a pair of thiophene bridges has the narrowest bandgap and the deepest HOMO,and the narrow bandgap is mainly caused by the deeper LUMO level.PETEHIDT with thiophene groups on both sides has shallow HOMO and LUMO,and the calculated bandgap was the widest.All molecules have poor photovoltaic performance with PC61 BM as acceptor and their external quantum efficiency responses are low over the entire wavelength range.The hole mobility of the active layer is modest,with a 10-7 order of magnitude.Among them,PETEHIDT has the best performance with efficiency of 1.56%,probably because of its large π conjugated system and high hole mobility.