Synthesis Of The Polymer Donors Based On Thieno[3,4-b] Thiophene And Their Application In Organic Solar Cells

Conjugated polymers have attracted considerable attentions in organic electronics due to their distinct characteristics of the electronic properties,structure diversity,light weight,and large-area fabrication of flexible devices via ease of solution processing.Nowadays,power conversion efficiency(PCE)of over 11 % in polymer/fullerene solar cells(PSCs)have been realized with continuous effort in design of new building blocks,backbone modification,side-chain engineering and device optimization.Hereinto,molecular skeleton,such as configuration,conformation,and planarity,has been put forward to regulate the energy levels,intermolecular interactions and carrier mobility,as well as the photovoltaic performance.In this thesis,we designed and synthesised a seires of novel Tb T-based polymer donors.Successfully achieved the porpose to regulate the properties of materials and solar cell devices though altering the configuration of Tb T construction unit,the regioregularity of molecular skeleton and the proportion ratio of different units in terpolymers,and eventurally modified the power convertion efficiency of organic solar cells.Firstly,we successfully developed thiazole-induced strategy to construct efficient photovoltaic materials via incorporating one thiazole unit into the backbone of non-fluorinated quinoid polymer PBDTTT-E-T,which is benificial from the desirable molecular skeleton with enhanced intermolecular interactions and decreased HOMO energy levels.Furthermore,the influence of molecular regioregularity with different orientations of Tb T was investigated,due to more planar molecular conformation,stronger crystallinity and excellent phase separation,a superior PCE of 9.36 % of the PBTz T-4-based photovoltaic device was obtained,slightly higher than that of PBTz T-6(PCE=8.52 %)and showed a signficant increase of 50 % compared to PBDTTT-E-T(PCE=6.21 %).More importantly,compared with random polymers,the regioregular copolymers exhibited slightly enhanced red-shifted absorption,crystallinity and compariblity with PC71 BM,leading to more desirable efficicency for PBTz T-4R-based devices(PCE=9.63 %)with higher JSC of 17.56 m A/cm2,which can be comparable to the classical polymer PTB7-Th,as well as one of the highest values for the TT-based solar cells.This work reveals that the orientation of asymmetric unit along the polymer backbone play a crucial role and should be taken into account in future molecule design.Secondly,we adopted a ternary copolymerization strategy to regulate polymer solubility and molecular aggregation.A series of D-A1-D-A2 random polymers based on different acceptors,strong electron-withdrawing unit ester substituted thieno[3,4-b]thiophene(TT-E),and highly planar dithiazole linked TT-E(DTz TT)were constructed to realize the regulation of molecular aggregation and simplification of device fabrication.The results showed that as the relative proportion of TT-E segment in the backbone increased,the absorption evidently red-shifted with a gradually decreased aggregation in solution,eventually leading to the active layers that can be fabricated at low temperature.Furthermore,due to the excellent phase separation and low recombination,the optimized solar cells based on the terpolymer P1 containing 30 % of TT-E segment exhibit high power conversion efficiency(PCE)of 9.09 % with a significantly enhanced fill factor up to 72.86 %.Encouragingly,the photovoltaic performance is insensitive to the fabrication temperature of the active layer,and it still could maintain high PCE of 8.82 %,even at room temperature.This work not only develops the highly efficient photovoltaic materials for low temperature processed PSCs through ternary copolymerization strategy but also preliminarily constructs the relationship between aggregation and photovoltaic performance.