Design,Synthesis And Photovoltaic Properties Of Small-molecule Donors Based On Porphyrin

With the increasing of fossil energy and the increasing environment pollution,people pay more and more attention to the development and utilization of renewable energy technology.Organic photovoltaic(OPV)cell is considered to be the most promising technology to solve the energy problem,since the technology can directly convert solar energy into electricity.OPVs have many unique advantages,mechanical flexibility and solution-processing technology for large area.To date,the highest power conversion efficiency(PCE)of polymer solar cells can be over 12%,but the intrinsic batch to batch variation issue of polymers could hamper the performance reproducibility for possible commercialization of OPV.In contrast,small molecular(SM)OPV devices demonstrate many prominent advantages,such as,less batch to batch variation for performance due to their uniform and defined molecular structures,easily tuned absorptions and energy levels resulting from a dedicated chemical structure design.For the past few years,the PCEs of the single layer devices based on SMs exceed 11% for the joint efforts between researchers.However,there is still a long way to go for the commercial applications,the stability and life of the devices is an important obstacle to the development of organic solar cells.Hence,developing of new efficient and stable donor and acceptor materials is still the focus of solar cell research.Since,porphyrins were used as electron donors in SM-OPV,they have been attracted extensive attention due to the excellent photovoltaic properties of high extinction coefficients ε,large coplanar structure and easily tuned,photo-and electro-chemical properties through the functionalization of the peripheries(meso and β-positions).Small molecules based on porphyrin donor materials show high performance in OPV devices.This thesis focuses on the expandsion of the porphyrin-based small molecules and the characterization of the photovoltaic properties of the small molecules.In chapter 2,three A-D-A type small molecules based on porphyrin have been designed and synthesized.Organic solar cells used the new small molecules as electron donor material were fabricated and all of the devices exhibited good photovoltaic performance.The best devices performance was achieved for(DPP-ZnP-E)2-Ph-based devices with a PCE of 6.42%,and a short-circuit current(Jsc)of 16.34 mA cm-2.In chapter 3,porphyrin dimer(DPP-ZnP-E)2 linked with diethynylene exhibits strong absorption in Uv-vis-NIR,but the ≡C—C≡ between two porphyrin unit affects their intermolecular π-π stacking because it can be twist to some extent.Hence,we replace diethynylene with ethyny to linked two porphyrin units and design and synthesize ZnP2-DPP.The resulted material exhibits broader light absorption to 968 nm in film and a low energy band gap of 1.28 eV.A PCE of 8.45% is obtained in bulk heterojunction(BHJ)organic solar cells based on ZnP2-DPP with a excellent short-circuit current of 19.65 mA cm-2.The optical devices show high external quantum efficiency from 300 to 900 nm,indicating that it is a promising candidate material to achieve high PCEs for tandem and ternary organic solar cells.In chapter 4,two porphyrin oligomers Zn2-DPP3 and Zn3-DPP2 are sythesized,and the both of them show broad light absorption.We use CV and optical band gap to calculate their HOMO and LUMO energy levels.Since Z n2-DPP3 shows too low LUMO energylevel(-3.95 eV),which does not match that of PCBM,the devices based on Zn2-DPP3 exhibit a very low PCE.However,those based on Zn3-DPP2 show a PEC of 5.51%.In chapter 5,we present a feasible and efficient molecular engineering approach with 4-methoxy modified thiophene as the conjugated side chain for porphyrin-based small molecules,with different electron acceptor as arms to design and synthesize BTEZnP-TOM and DPPEZnP-TOM.The both show lower HOMO energy levels,and the devices based on DPPEZnP-TOM exhibit better photovoltaic performance with a PCE of 9.59%,and a Jsc of 19.79 mA cm-2 due to the broader absorption.In chapter 6,we design and synthesize BTZnP2-IN and BTZnP2-RH,in which two porphyrin units were linked to 2,1,3-benzothiadiazo by ethynylene bridges to form a porphyrin dimer,and 1H-indene-1,3(2H)-dione or 3-ethylrhodanine was selected as the acceptor unit.The BTZnP2-IN and BTZnP2-RH show lower HOMO energy levels and wide absorption leading to improved Voc,Jsc values.Due to the more ordered π-π stacking of BTZnP2-RH and the higher hole mobility of BTZnP2-RH-based devices,the BTZnP2-RH:PC71BM based devices display a higher Jsc of 17.49 mA cm-2,and a PCE of 10.02%.