Research On Organic Small Molecule And D-A Copolymer Based On BDT Unit Synthesis And Performance

Organic solar cells are favored by scientific researchers and the social business community because of their advantages in preparation and processing by spraying solutions,their flexibility to bend easily,the materials required for synthesis are easy to obtain,the weight of finished products is small,and the texture is light and transparent.However,there is still much work to be done in commercialization,in the current energy shortage environment.It is imperative to accelerate the development of materials based on organic solar cells.The absorption spectra,energy level matching and carrier mobility of organic small molecules and conjugated polymers play a decisive role in the photovoltaic energy conversion efficiency of organic solar cells.In order to design high-efficiency organic small molecules and polymer donor materials,this paper selects high-efficiency donor benzothiadiphene?BDT?as the main building unit,and gives the/receptor level matching as a route,supplemented by The adjustment of bulk material structure,design and synthesis of three photovoltaic materials,respectively,based on BDT and triple thiophene synthesis of small organic molecules,with benzothiadiazole and with 3,5-diaza-1,7-dithio The Donor-Acceptor?D-A?type conjugated polymer synthesized by spiro[3,3]heptane was studied in detail.The molecular structure,composition,morphology,and composition of the synthesized polymer were determined by ¹H-NMR,density functional theory calculation,atomic force microscopy?AFM?,thermogravimetric analyzer?TGA?,ultraviolet analyzer,and cyclic voltammetry.The thermal properties,light absorption properties and electrochemical properties were analyzed and characterized.At the same time,the three materials were used as donors,and the ITIC materials were used as acceptors to prepare organic photovoltaic devices.The photovoltaic devices were characterized and analyzed.The main research work is as follows:?1?2,2':5',2''-Terthiophene?TT?structure has a relatively good electron-withdrawing property and an intermolecular?-?bond force due to its good planarity.In addition,changing the length of the alkyl chain or increasing the hetero atom at the modifiable site can well regulate its solubility and band gap.These features are well suited to the material structure requirements of organic photovoltaic devices.2,2':5',2''-Terthiophene was designed and synthesized as a double-armed,Radanine as a molecularly terminated acceptor unit,Stille coupling reaction with BDT plus bismuth tin species modified with alkylthiothiophene to obtain organic donor polymer materials?TT-BDST-TT?),TT-BDST-TT exhibits good electron cloud distribution and thermal stability.And the photovoltaic performance is better.When the device is prepared,the solubility in the solution is poor because the solubility is lowered due to the excessive chain length of the alkylthiothiophene of the BDT unit.Although the performance as an organic small molecule photovoltaic material is good,it is impossible to fabricate a device.?2?In order to investigate the effect of the length of the alkyl chain attached to different sites in the acceptor unit on the donor-acceptor?D-A?type conjugated polymer on the photovoltaic performance of the material,benzothiene?BDT?was used as the core unit.The D-A type two-dimensional conjugated polymer BDT-BTz was designed and synthesized with modified benzothiadiazole.Testing the photoelectric properties,electron mobility and film morphology of the donor material.The results show that The introduction of a chain-length alkyl chain on the benzene ring of benzothiadiazole?BTz?has little effect on its highest occupied orbital?HOMO?energy level,but has a great influence on the performance of the photovoltaic device prepared.The organic polymer not only has a uniform planarity of electron cloud distribution,but also has good electron withdrawing properties of the acceptor unit,which is favorable for electron-hole migration.Its thermal stability can be used to prepare photovoltaic devices,and the solubility of the film is good.Organic photovoltaic devices based on BDT-BTz?ITO/PEDOT:PSS/BDT-BTz:ITIC?1:1,w/w?/Ca/Al?show good photovoltaic performance.When 0.5%DIO was added and annealed,the open circuit voltage reached 0.84 V and the maximum energy conversion efficiency was 3.37%.?3?A D-A type conjugated polymer photovoltaic donor material based on BDT as the main donor unit and 1,5-dithia-3,7-diazaspiro[3.3]hepta-2,6-diene as the A unit was designed and synthesized.BDT-NSd.The thiophene unit is attached to both sides of the acceptor unit,and the alkyl chain is introduced at the thiophene three position;and the thiophene alkyl chain of the BDT unit is replaced with a short chain to investigate the effect of the alkyl chain length on the photovoltaic performance of the polymer.The experimental results show that the polymer BDT-NSd has good solubility and film formation;it has broad spectral absorption at 300-700 nm.Due to the strong electron-withdrawing effect of the acceptor unit,it has a low highest occupied molecular orbital?HOMO?level of-5.41 eV.The conjugated polymer has a good match with the acceptor material ITIC.When blended with ITIC?1:1.1,w/w?,the PCE value of the photovoltaic device is 2.14%with the addition of 0.5%DIO.Jsc,Voc,and FF are 2.41 mA.cm^-2,0.85 V,and 57%,respectively.Although the conjugated polymer has excellent open circuit voltage and fill factor performance,because the alkyl chain is too small,the contact area of the acceptor is too small to form an effective electron-filled stack,which is made of the donor material.The energy conversion efficiency of the device reached 2.14%,and the main reason for achieving this value is the advantage of the ITIC acceptor material.