Research On The Active Layer Regulating And Thermal Stability Of Organic Solar Cells Containing Imide Benzotriazole Polymers

Synergistic development of organic photovoltaic materials and devices engineering has boosted the highest calibrated power conversion efficiency(PCE)of organic solar cells(OSCs)over 18%.The significant progress potentially makes OSCs a promising candidate for commercial application.Wide-bandgap(WBG)polymer donors combined with non-fullerene acceptors(NFAs)post vast prospects in non-halogenated solvents processing,ternary OSCs,thick film devices and so on.However,it keeps a critical role to further develop high efficiency OSCs with excellent stability and understand the relationship between the optimization of active layers and degeneration in devices due to the complicated film formation kinetics.In this dissertation,active layers containing wide-bandgap imide-functioned benzotriazole(Tz BI)polymer donors are carefully optimized with various processing methods.The improved performance of OSCs with morphological modification,the degeneration of devices under thermal stresses,thermal stresses on electrical properties and the amorphous phase degeneration for OSCs under thermal stresses has been explored.In chapter 2,the photovoltaic parameters of all-polymer solar cells(all-PSCs)can be enhanced upon replacing a certain weight ratio of electron-donating polymer PTz BI-o F with a widely used wide-bandgap polymer donor PM6.The PTz BI-o F polymer donor exhibits good miscibility with PM6 because of the similarly surface energy.The optimized ternary PTz BI-o F:PM6:PFA1 device presents an impressively high PCE of 16.3%with good thickness tolerance,and the efficiency remains 15%on a device with enlarged effective area of 1 cm~2,demonstrating the great potential for future applications.Detailed morphology studies demonstrate that the incorporation of PM6 results in mitigated interfacial diffusion and the occurrence of a pure fiber phase with controllable crystal coherent lengths(CCLs).Meanwhile,the incorporation of PM6 also reduces non-radiative recombination energy loss,and enhances the charge extraction and transportation.In chapter 3,by combining a WBG conjugated polymer P2F-EHp and NFAs of IT-4F and IT-4Cl,OSCs can be processed with non-chlorinated toluene:o-xylene co-solvent.Device based on IT-4Cl presents promising photovoltaic performance with PCE of about 12%without solvent vapor annealing post-treatment.Detailed investigation of film morphology demonstrates that co-solvent appears to assist the manipulation of crystal coherent lengths and effectively decrease the phase separation of corresponding blend films.This material system is also compatible with low-cost blade-coating technique using toluene:o-xylene co-solvent,and a high efficiency of 10.1%can be achieved by blade-coating the P2F-EHp:IT-4F:IT-4Cl active layer in the air.Long-term thermal stability test reveals that the degeneration of devices has relationship with the domain size of active layers processed with different solvents,indicating the decay of morphology may be occurred in D-A mixed regions.In chapter 4,the sequential deposition method is used to fabricate photoactive layers of all-PSCs comprising of a polymer donor PTz BI-o F and a polymer acceptor PS1.The film morphology can be manipulated by incorporating amounts of dibenzyl ether(DBE)additive into PS1 layer.Detailed characterizations reveal that the sequential deposition assisted with DBE additive play a key role in maximizing the crystallinity,increasing“face-on”arrangements relative to substrates and regulating the film phase separation,thus improving carrier transport and generation,and suppressing charge recombination.The optimized all-PSCs delivers an enhanced PCE of 15.21%along with improved carrier extraction and suppressed charge recombination.More importantly,the optimized all-PSCs remain over 90%of their initial PCEs under continuous thermal stress at 65°C after 500 h,superior to the blend casting counterpart.Detailed charge recombination and transportation analysis illustrate that aged blend casting all-PSCs may encounter both trap-assisted recombination and bimolecular recombination,causing faster decreased device performance under thermal stress.In chapter 5,thermal stable OSCs by integrating an electron-donating polymer PTz BI-d F and two NFAs of L8BO and Y6 are demonstrated,which feature similar structures yet different thermal and morphological proprieties.The OSCs based on PTz BI-d F:L8BO:Y6 achieve a promising PCE of 18.26%as well as excellent long-term thermal stability over 1400 h under85℃continuous heating.The morphological features in terms of crystalline coherence length(CCL)can be gradually regulated by the weight ratio of L8BO:Y6.Additionally,the occurrence of melting point depression and lower enthalpy in PTz BI-d F:L8BO:Y6 films can prohibit the amorphous phase to cluster,and consequently overcome the energetic traps accumulation aroused by thermal stress,which is a critical issue in high efficiency NFA-based OSCs.