Design And Synthesis Of Diphenylpyranylidene Conjugated Polythiophene And Their Application In Organic Solar Cells

Nowadays,there has the energy shortage in the world,therefore developing new energy has received extensive attention.The solar energy has various advantages,such as abundant resources and wide distribution,becoming the focus of people's research.Organic solar cells?OSCs?have been widely developed in recent decades.Among them,polymer organic solar cells?P-OSCs?have attracted much attention in recent years due to it has the advantages of low cost,light weight and easy preparation.It also have potential on large-area production,good flexibility and convenient carrying.The active layer of mainly consist of electron donating conjugated polymers and electron accepting fullerene.Most of the donor materials are soluble polythiophenes and their derivatives.Poly?3-hexylthiophene??P3HT?has been widely used in the early stage,but it can only absorb some visible light,the photon utilization ratio is low,and the solar light could not be fully utilized.Later,new polymer donor materials with alternating electron donor-acceptor?D-A?conjugated structures on the main chain were developed.Although the D-A conjugated polymer can effectively expand the optical absorption range,the absorption intensity is weak in the ultraviolet region and part of the visible light region.Compared with polymer,small molecule owns varied molecular structure,easy purification and no batch difference during the production.Ordered nanophase separation structure,which has the advantages of higher carrier mobility,has been widely studied in more than a decade,setting off another research boom in the field of OSCs.In the design of small molecular materials,Oligomer-like small molecule donor material is the most prominent.The most representative donor material is acceptor-donor-acceptor?A-D-A?oligothiophene structure.However,the development of traditional donor-receptor?D-A?small molecule donor materials is relatively slow,mainly due to the small overall light absorption range,wide band gap and so on.In order to promote the development of traditional push-pull structure small molecules,and to pursue more extensive light absorption and narrow band gap,new attempts should be made.In order to improve the light absorption range of polymer and small molecule donor materials and the photoelectric conversion efficiency?PCE?of organic solar energy,four series of polymers and two small molecule donor materials were designed and synthesized using Diphenylpyranylidene?DPP?as raw materials,and their photophysical and electrochemical properties were studied.The results of this work were as follows:In the first part,the DPP groups are used as conjugated side chains,and the molecular monomers T1 and T2 of two different conjugated bridges are designed.The energy level distribution and geometry of the monomers T1and T2 were calculated by Density functional theory?DFT?,and their molecular conjugation and planarity were discussed.The P1 and P2 series and P3 and P4 series polymer donor materials were synthesized by Grignard metathesis method and Stille coupling method,and their structures were characterized.The light absorption,electrochemical and photovoltaic properties were studied.The absorption spectra indicates that as the conjugated main chain of thiophene or benzodithiophene increases,the light absorption range increases and gradually red-shifted,covering the ultraviolet region 300-400 nm and the entire visible region.Photoluminescence spectroscopy indicates that energy transfer occurred in the molecule.As the conjugated unit of the main chain increased,the maximum emission peak gradually red-shifted.Cyclic voltammetry shows that a series of polymers have higher Highest occupied molecular orbital?HOMO?energy levels,which can be better matched with PC₆₁BM to ensure higher open circuit voltage(V_oc).Finally,a series of synthesized polymers were used as donor materials,and PC₆₁BM was used as the acceptor material to prepare P-OSCs.The results show that the photovoltaic cells have a good V_oc and the PCE is up to 0.59%.In the second part,according to the calculation of DFT theory,the small molecules Y1 and Y2 with extensive light absorption push-pull structure D-A were designed and synthesized.And they were used as an active layer material in SM-OSCs.The structure was characterized and the light absorption,electrochemical and photovoltaic properties were studied.The results show that the two small molecules show good thermal stability,and exhibit a wide light absorption and two maximum absorption peaks.Two molecules had same HOMO energy level and narrow band gap,moreover,the evolution is consistent with the theoretical calculation.Finally,SM-OSCs were prepared using Y1 and Y2 as donor materials and PC₆₁BM as acceptor materials.Photovoltaic properties indicate that the two small molecules exhibit a maximum PCE of 1.0%.In this study,the DPP group is first used as active layer material in small molecule solar cell.As shown in results,even the PCE is not ideal,but it shows a wide range of light absorption and narrow band gap.Thus,DPP group is a potential donor material.