The Application Of Subphthalocyanine/Triphenylamine Derivatives In Photodetectors

Subphthalocyanine（SubPc）is a type of aromatic cone-shaped molecules with a conjugated 14πelectron system.In recent years,SubPc and its derivatives are widely used in organic light-emitting diodes（OLEDs）,organic photovoltaics（OPVs）,organic field-effect transistors（OFETs）,and organic photodetectors（OPDs）due to their advantages of thermal stability,strong absorption coefficient,and high carrier mobility.Triphenylamine（TPA）is a three-dimensional,propeller-shaped conjugated aromatic amine molecule with a nitrogen atom center.Its derivatives are usually used as donor materials in photoelectric devices for their good hole transport properties,photothermal stability,and photochemical properties.We synthesized four SubPc derivatives and four triphenylamine-tetrahydropyrroloquinolinone derivatives（TPAs）to investigate their photophysical and photoelectric properties.Additionally,we explored their applications in OPDs.The main research contents of this work are listed as follows.1.P-type F-BSubPc,Cl-BSubPc,Br-BSubPc,and n-type CN-PhO-BSubPcF₁₂SubPc derivatives were synthesized.These SubPcs exhibit good thermal stability and two absorption bands in the UV-vis region.The CV and SCLC tests display that F-BSubPc,Cl-BSubPc,and Br-BSubPc have higher HOMO energy levels and hole mobilities,making them suitable as p-type donors.On the other hand,CN-PhO-BSubPcF₁₂ shows the low LUMO/HOMO energy levels and high electron mobility,making it ideal as a hole-blocking n-type acceptor.The molecular FMOs and dipole moments calculations by density function theory（DFT）reveal that four SubPcs exhibit intramolecular charge transfer（ICT）properties.From the steady-state and transient PL spectral analysis,it can be found that efficient photogenerated charge transfer can occur in both p-type SubPcs/C₆₀heterointerfaces and p-type SubPc/n-type SubPc planar heterojunction.It indicates that these SubPc derivatives could be used as the heterojunction photosensitive layers.F-BSubPc/C₆₀,Cl-BSubPc/C₆₀,and Br-BSubPc/C₆₀ planar heterojunctions,and BSubPc/CN-PhO-BSubPcF₁₂isotype p-n SubPc heterojunction were utilized to fabricate OPDs.Four devices all exhibit stable UV-vis dual-band response and self-powered characteristics.Under the 570 nm LED excitation without bias,the Br-BSubPc/CN-PhO-BSubPcF₁₂ device achieves a high responsivity of 0.13 A/W,a peak EQE of 29.2%,and an extremely low dark current density of 9.60×10^-10 A/cm².The isotype p-n SubPcs heterojunction with better interfacial contact resulted in a larger depletion region,lower trap density,and lower carrier recombination rate.This is beneficial for the efficient dissociation and balanced transport of photogenerated carriers,leading to excellent device performance.Moreover,a secure communication strategy was successfully demonstrated by dual-band optimal OPD.2.Four D-π-A molecules o-PQOTPA,m-PQOTPA,p-PQOTPA and p-FPQOTPA were synthesized using TPA as electron donor,benzene ring asπ-bridge and tetrahydropyrroloquinolinone as electron acceptor.Their photoelectric properties were investigated as the donor and acceptor units substituted in the ortho,meta,and para positions on theπ-bridge.The thermal stability,photophysical property,energy level structure,and carrier transport property of these molecules were characterized using TGA,UV-vis absorption,PL,TRPL,CV,and SCLC measurements.In addition,the molecular FMOs,dihedral angle,dipole moments,and electrostatic potential（ESP）were analyzed using DFT calculations.It is found that p-PQOTPA with donor and acceptor units substituted at the para position on theπbridge exhibits a high molecular planarity and a large dipole moment.The straight-chain conformation increases the charge transport rate within the D-π-A molecular chain,resulting in a strong ICT characteristic and high hole mobility.The double-donor ternary active layers were constructed by TPAs and the above isotype p-n SubPcs heterojunction to prepare OPDs.All devices exhibit stable UV-vis dual-band photoresponse.Especially,the p-PQOTPA-based OPD presents the best photodetection performances with a low dark current density of 8.64×10^-7 A/cm²,a responsivity R of 0.13 A/W,and a detectivity D^*of 2.50×10¹¹ Jones under 365 nm illumination and-1 V bias.Its high performance could be ascribed to the reduced dark current resulting from the high LUMO level of TPAs in the dual donor.Moreover,the TPA and p-n type SubPcs could form a well molecular packing and exhibit efficient intermolecular charge transfer between TPA and CN-PhO-BSubPcF₁₂,which synergistically enhance the separation and transport of photogenerated carriers.3.Two types of ternary heterojunction photomultiplication OPDs（PM-OPDs）were demonstrated by introducing a hole-transporting self-assembled monolayer（SAM）and planar strong acceptor F4-TCNQ.Through the modification of ITO with SAM,the surface work function increases and the contact resistance between ITO and active layer decreases.The fabricated PM-OPD with the photosensitive layer of P3HT:PCBM:F4-TCNQ（100:1:0.02,wt%）shows a peak EQE of 268659% at-20 V,which is significantly higher than that of the PEDOT:PSS-based control device（186270%）.The introduction of SAM also improve the stability of PM-OPDs.Furthermore,we prepare ternary heterojunction UV PM-OPDs based on 2PACz and TPAs:CN-PhO-BSubPcF₁₂:F4-TCNQ（100:1:0.02,wt%）.The optimized p-PQOTPA-based device exhibits the best photomultiplication characteristics with the peak EQE,R,D*,and LDR values of 150490%,443.0 A/W,1.09 × 10¹⁴ Jones,and 105.0 d B at-15 V,respectively.The outstanding device performance can be attributed to several factors.SAM played an important role in hole extraction.The p-PQOTPA:CN-PhO-BSubPcF₁₂ in ternary heterojunction facilitate the hole transport and electron trapping.The planar strong acceptor F4-TCNQ induce an optimal molecular arrangement and improve hole transport in the active layer.