Investigation Of The Photothermal Durability Of Dye-sensitized Solar Cells With Cobalt-based Electrolyte

Dye-sensitized solar cell(DSSC),as one of potentially low-cost photovoltaic technology,is for the conversion of abundant solar light to clean electric power.DSSCs with adjustable color palette and transparency could enable the supply of electricity and day-light synchronously,which is very suitable for building-integrated photovoltaics(BIPVs).However,the excellent long-term stability of high-efficiency DSSC devices in combination with cobalt-based electrolyte restrict the large-scale commercial practical application.Photosensitizing dyes,as one of kernel core of a DSSC,play vital roles in harvesting light and charge generation,thus affects the longevity of DSSC devices.Focusing on the issue,this paper systematically investigates the different structure of photosensitizing dye upon the excited state and interfacial charge transfer kinetics,all of which are closely associated with the device performance,as well as the inherent origin of device degradation analysis.The important results are described as following:Through facile use of intramolecular Friedel-Crafts alklation reaction,we flexibly construct two aromatic polycycles phenalenothiophene(PT)and benzoindenothiophene(BIT)based-naphthalene,which is further tethered with two 4-hexylphenyl solubilizing groups.The novel chromophores PT and BIT is functionalized with ancillary electron-donor bis(4-(hexyloxy)phenyl)amine(DPA)and electronacceptor benzothiadiazol-benzoic acid(BTBA)to design two donor-acceptor organic dyes H1 and H2.Resorted to density functional theory(DFT)calculation,photophysical and electrical measurements,the impact of energy level,light-harvesting,charge-transfer dynamics as well as photovoltaic performance upon the polycycles PT and BIT were systematacially investigated.Those two dye were employed to fabricated DSSC with cobalt electrolyte.Dyes H2 were tested for coadsorbate-free DSSCs with a cobalt redox electrolyte,presenting fairly good PCEs of 10.3%.With respect to the H2 cell,the H1-based cell with high photovoltage output displaying an encouraging durability during full-sunlight soaking at 60 ? for 1,000 h.Based on the polycycles PT and BIT,low-energy-gap photosensitizers H3 and H4 with deficient electron-acceptor benzothiadiazol-ylethynyl-benzoic acid(BTEBA)are prepared.Compared to BTBA-based dyes H1 and H2,DFT calculation reveals that H3 and H4 with BTEBA significantly feature ?100 me V stablized lowest unoccupied molecular orbital(LUMO)energy levels.Femtosecond fluorescence decay and nanosecond transient absorption measurements suggest that the two low-energy-gap photosensitizers present efficient charge separation yields in DSSCs.The H4 cell achieves a high power conversion efficiency of 10.9%,owing to the broadened spectral response,while the H3 cell presents a better retention ratio of power conversion efficiency under full-light soaking at 60 ? for 1000 h The self-assembling molecular layer on the surface of titania with H3 is more compact and better organized,mitigating the interfacial charge recombination.Based on the polycycles PT segments,the coplanar aromatic polycycles benzophenanthrothiophene(BPT)is designed via the lateral ?-extension of PT,which is decorated with bis(4-(hexyloxy)phenyl)amine ancillary electron-donor and conjugated with electron-acceptors benzoic acid(BA),BTBA,BTEBA,2-cyanoacrylic acid(CA)to prepare donor-acceptor organic dyes HW5,HW6,HW7,and HW8.The impacts of electron-acceptors upon energy level,energy gaps,dynamics of excited state,interfacial charge transfer,and cell durability were systematically investigated.Both dye solutions in THF and grafted on oxide film,the BA,BTBA,BTEBA-based dyes exhibit prolonged excited state lifetimes,while the CA-based dye presents shorter lifetimes.In conjunction with a cobalt electrolyte,the dyes with CA,BTBA,BTEBA as electron-acceptor display outstanding retention rates of PCE after 1,000 h aging test under the soaking of full sunlight at 60 ?.Aiming to meet the requirements for furtutre commericial application of DSSC,novel polycyclic heteroaromatics benzoindenothieno-benzoindenothiophene(BIT2)and phenalenothieno-phenalenothiophene(PT2)are designed and synthesized via p-extension based on the polycycles BIT and PT,which can be used along with indenothieno-indeno thiophene(IT2)and benzophenanthrothienobenzophenanthrothiophene(BPT2)for the construction of a series of organic DSSC dyes to clarify the effect of lateral p-extension.Both voltammetric measurements and theoretical calculations have disclosed that lateral p-extension can bring forth a downward shift of LUMO energy level of dye molecules that use the ethynylbenzothiadiazole-benzoic acid(EBTBA)electron-acceptor.These dyes can be employed to make semitransparent DSSCs with goldenrod,red,and sapphire blue colors.For the first time an over 10% power conversion efficiency at the AM1.5G conditions has been reached by a semitransparent solar cell with enjoyable blue color.The red and blue solar cells made with dyes characteristic of laterally enlarged p-conjugation present good durability after 1000 h full sunlight soaking at 60 ?.The result presented here exhibits a potential application for building-integrated photovoltaics.