Design,Synthesis And Device Performance Characterization Of Novel Conjugated Organic Photovoltaic Materials

Compared to inorganic solar cells,organic solar cells(OSCs)have attracted considerable attention due to their unique advantages of light weight,low cost,and the ability to fabricate flexible and semi-transparent devices.As the main part in the photoelectric conversion process,the active layer composed of organic materials is the key to improve the photovoltaic performance of OSCs.Developing novel and efficient organic photovoltaic materials have become an important research issue in this field.In this dissertation,starting from the structure modification of donor and acceptor photovoltaic molecules,we realized the finely tune of light absorption characteristics,molecular energy levels and aggregation characteristics of active layer,and fabricated a series of highly efficient OSCs.Furthermore,we carried out in-depth studies of the correlations among the chemical structure,photoelectric properties,molecular packing characteristics,charge transport properties,microscopic morphology,and device performance.The main achievements and conclusions are as follows(1)A new 2D-conjugated small molecular acceptor named BP-4F,based on BDTP as an electron-donating core,is designed and synthesized.The absorption spectrum,molecular energy levels and charge transport performance of the molecule are regulated by the enlarged conjugate area.When blended with the wide bandgap polymer PM6,the OSCs achieve an encouraging power conversion efficiency(PCE)of 14.2%with an open-circuit voltage(Voc)of 0.90 V,a short-circuit current density(Jsc)of 21.9 mA cm-2,a fill-factor(FF)of 0.72,and an energy loss(Eloss)of 0.59 eV.Furthermore,the devices show an excellent storage stability and photo-stability(2)Two asymmetric small molecular acceptors(IDTP-4F and IDTTP-4F)based on dithieno[3,2-b:2'3'-d]pyrrol(DTP)with S-shape and C-shape confirmations,respectively,are designed and synthesized.The two acceptors exhibit similar absorption spectra and energy levels.Three wide bandgap polymer donors(PM6,S1,and PM7)were chose to investigate the relationship between molecular conformation and photovoltaic performance.Consequently,S-shape IDTP-4F performed obviously better than the C-shape IDTTP-4F counterparts in OSCs regardless of the polymer donors,which confirms that S-shape conformation performs better than the C-shape one.Moreover,the champion PCE afforded by PM7:IDTP-4F is as high as 15.2%.(3)A novel asymmetrically noncovalently fused-ring electron acceptor,namely IDST-4F is synthesized by unilaterally introducing alkylthio-substituted thiophene as?-bridges.IDST-4F exhibits a broader and stronger absorption,higher-lying energy levels,larger dipole moments and suppressed crystallinity than its symmetric counterpart(ID-4F).when blended with wide polymer donor PM6,the optimized devices based on IDST-4F display an excellent PCE of 14.3%with a Voc of 0.82 V,a Jsc of 24.9 mA cm-2,and an FF of 0.70.On the contrary,the devices based on ID-4F only achieve a lower PCE of 6.4%with a Voc of 0.73 V,a JSC of 13.5 mA cm-2,and an FF of 0.65.Furthermore,the PM6:IDST-4F-based OSCs possess excellent storage and thermal stability.(4)The acceptor unit BFT based on fluorinated ?-bridges is incorporated into PM6 polymer with different contents,and a series of polymers PF1,PF2 and PM6F are synthesized.With the increasing BFT content,the polymers display gradually red-shifted absorption spectra,lower-lying energy levels,enhanced aggregation.When blended with acceptor material Y6,the terpolymer PF1 with 30%of BFT segment exhibits excellent efficiency as high as 17.3%,with a VOC of 0.87 V,a Jsc of 26.32 mA cm-2,and an FF of 0.76.