Design, Synthesis And Performance Research Of Linker Receptor Photovoltaic Material

Organic Solar Cells（OSCs）,using organic semiconductor materials as photoelectric conversion materials,have experienced rapid development over the past few decades.The highest energy conversion efficiency（PCE）has reached over 19%,meeting the primary requirements of various commercial applications,such as flexible wearable devices,indoor photovoltaics,and building integration.For practical application,it is essential to comprehensively evaluate the"efficiency-cost-lifetime"of OSCs,which is commonly known as the"golden triangle"for photovoltaic technology.While industrial synthesis have great protentional in reducing the synthesis costs,the cost issue related with the device processing can be further alleviated via the roll-to-roll printing of OSCs.However,the life time of OSCs remains a bottleneck.For the long-term device operation,the instability issues can be caused by the external factors such as the strong ultraviolet radiation and moisture instability.And most importantly,the thermal relaxation of the donor-acceptor blend film destructs the nanoscale bicontinuous interpenetrating network of the heterojunction.To improve the thermodynamic stability of the blend phase domains,appropriate Flory-Huggins interaction parameters（χ）are necessary.Additionally,increasing the glass transition temperature（T_g）of the acceptors can suppress interface diffusion and enhance the dynamic stability of the acceptor phase domains.The widely-used PM6:Y6system has been suggested to have a smallχvalue,and the T_gvalue of Y-series small molecule acceptors is also relatively low,so that the active layer of PM6:Y6 was identified to be nether in thermodynamics or kinetics stable states.Therefore,it is very important to appropriately increase theχvalue of the blend films as well as the T_gvalue of the acceptors.Currently,polymer acceptors that use polymerized small-molecule acceptors（PSMAs）can ensure high morphology stability.However,PSMAs cannot overcome the inherent disadvantages of polymers,particularly the batch-to-batch variation of molecular weights.This variation leads to inconsistent device performance between batches,which originates from the Stille-coupling reaction used in polymerization as this method cannot accurately control the polymerization process.To address this issue,oligomer acceptors with definite molecular structures and weights have been developed.They have great potential to achieve high power conversion efficiencies（PCEs）and device stability simultaneously.However,these acceptors still rely on the Stille-coupling reaction,which uses organotin reagents that are highly toxic and not suitable for green industrialization.Therefore,with the above concerns,this thesis adopts tethered strategy to synthesize the oligomer acceptors,and the main research contents of this paper are as follows:1.In this chapter,α-andβ-substituted thiophene units are chosen as the aromatic ring core,and two tethered dimer acceptor,TDY-αand TDY-β,are designed and synthesized.Furthermore,the structure-performance relationships of the two dimers are studied.By applying and other.It can be inferred from various characterization methods,including the2D¹H-¹H NMR NOESY spectrum,DFTB simulation,temperature dependent UV-visible spectrum,that tethered dimer molecules in solution have the obvious tendency to fold.Such a pre-aggregation state can effectively regulate the aggregation behavior in its blend with polymer donor.Moreover,the highχvalue and T_gof the dimers significantly inhibited the diffusion of acceptors into the donor phase,thus suppressing over-purification of the blend domains.As a result,PM6:TDY-αbased devices show the best photovoltaic performance,with the highest PCE of 18.1%,V_OCof 0.864 V,J_SCof 26.9 m A cm^-2,and FF of 78.0%.More importantly,the devices based on dimers can maintain more than 80%of the initial PCE values under continuous thermal aging at 80℃for 1000 h and under continuous light in the air for 1100 h.We extrapolated operational stability of TDY-αbased devices,and estimated an average T₈₀lifetime of about 35000 h（about 16 years）if operating average 6hours per day in actual open-air working condition at Beijing.2.In this chapter,halogen-substituted quinoxaline units are chosen as aromatic ring cores,and three tethered dimer acceptor,TDY-F,TDY-Cl and TDY-Br,are designed and synthesized.The structure-performance relationships of the dimers are then studied.Using the UV-visible spectrum and the 2D¹H-¹H NMR NOESY spectrum,it can be inferred that the dimers in solution present a stable folded conformation,due to the strong electrostatic interaction between the electron-deficient aromatic ring core of quinoxaline unit and the Y6units.As the atomic diameter of substituted halogen atom gradually increased,the stacking distances of dimers in the corresponding films also increased.This resulted in a decrease in their corresponding coherent length of crystals and the worse packing of the dimers.Among the devices,PM6:TDY-F based devices shows the best photovoltaic performance,with the highest PCE of 18.0%,V_OCof 0.866 V,J_SCof 26.7 m A cm^-2and FF of 78.0%.The PCE of PM6:TDY-Cl and PM6:TDY-Br are 17.4%and 17.2%,respectively.However,as the atom size of the substituted halogen atom gradually increases,the molecular mobility gradually decreased,and the T_gincreased.The T_gvalues of TDY-F,TDY-Cl and TDY-Br are 118℃,121℃and 123℃,respectively.Therefore,PM6:TDY-Br based devices show the best stability,maintaining more than 90%of the initial PCE after 1000 h of continuous thermal aging at 80℃or under continuous light in the air for 1200 h.And the extrapolation of operational stability of TDY-Br based devices indicates an average T₈₀lifetime of about13700 h.3.In the chapter,tetraphenylmethane is chosen as aromatic ring core,and a tetramer acceptor molecule TTY-4Ph is successfully synthesized.The central carbon atom in TTY-4Ph is sp³hybridized,resulting in bond angles are 109°28’,which gives the tetramer a regular tetrahedral spatial orientation with the four Y6 subunits.As expected,the obvious intramolecular interactions in solution can also be observed from the UV-visible spectrum.The PM6:TTY-4Ph based devices showed a PCE of 16.9%,V_OCof 0.864 V,J_SCof 25.8 m A cm^-2,FF of 75.8%.Notably,the V_OCcan reach about 0.90 V for unannealed devices.More importantly,due to the higher T_g（145℃）of TTY-4Ph and the relatively higherχvalue（0.99）,PM6:TTY-4Ph based devices show better stability.For thermal stability,the PCE decay only about 5%in the first 20 hours,and the stabilized PCE is about 91%.For the light-soaking stability,the PCEs decay only less than 10%after 500 hours under continuous light in the air,and the"Burn-in"stage is obviously suppressed.