Preparation And Optoelectronic Properties Of Bandgap Tunable Conjugated Polymers With Alkoxy Chains

Organic solar cells have the advantages of light weight,low-cost,flexibility and large area processing.The power conversion efficiency?PCE?of organic photovoltaic devices?OPV?has been developed from initially less than 1%to about 11%over 20 years.But the relatively lower PCE of organic solar cells is not acceptable for large-scale commercial production.Designing organic photovoltaic materials with low cost and high efficiency is an important strategy to promote industrialization of organic solar cells.Polymers with alkoxy chains are proved to be advanced materials for highly-performing OPVs.The incorporation of alkoxy chains can improve the solubility of polymers,make the backbone more co-planer,and broaden the range of absorption.Based on alkoxy side-chain modification and alternating copolymerization of electron donor donating unity with different acceptors,we designed and synthesized two series of polymers with2,2'-[2,5-bis?2-alkyloxy?-1,4-phenylene]dithiophone,and studied their photovol-taic properties.The main contents are as followings:1.Preparation of narrow band gap polymers and studying its photovoltaic properties.Threedonorunitswithdifferentalkoxychains,2,2'-[2,5-bis?2-ethylhexyloxy?-1,4-phenylene]dithiophone,2,2'-[2,5-bis?2–butyloc tyloxy?-1,4-phenylene]dithiophone and 2,2'-[2,5-bis?2-hexyldecyloxy?-1,4-pheny-lene]dithiophone,were synthesized as electron-donating units to copolymerize with 2,5-Bis?2-octyldodecyl?-3,6-di?thiophen-2-yl?pyrrolo[3,4-c]pyrrole-1,4?2H,5H?-dione as electron-deficient monomer to afford polymer P₁?P₂?P₃.All polymers have good solubility and good thermal stability with the thermal decomposition temperature of 5%weight loss above 340^°C.The optical band gaps of these polymers are all about 1.37 eV.The HOMO energy levels of P₁,P₂ and P₃locate at-5.21 eV,-5.15 eV and-5.13 eV,respectively.Solar cell devices based on P₁ present the best performance with a maxium power conversion efficiency of3.29%,with a Jsc of 12.68 mA/cm²,a Voc of 0.64 V and a FF of 0.41.2.Preparation of large band gap polymers and studying its photovoltaic properties.Through replacing DPP unit by 2-?2-butyloctyl?-5,6-difluoro-1H-benzo[d][1,2,3]triazole electron-deficient unit,we get Polymer P₄,P₅,P₆.These polymers have good solubility and thermal stability as well.The optical band gaps are nearly 2.05 eV.The HOMO levels of P4,P5 and P6 locate at-5.34 eV,-5.42 eV and-5.54 eV,respectively,which make the corresponding solar cell devices have higher open circuit voltage comparing to that of the polymer P₁,P₂ and P₃.Finally,Solar cell devices based on P₅ present the best performance with a maxium power conversion efficiency of 3.03%,with a Jsc of 7.17 mA/cm²,a Voc of 0.82 V and a FF of 0.51.