Photodetectors Based On Organic Small Molecule Materials

Organic small molecule materials have huge potential application in photodetectors （PDs） with high sensitivity, high speed, and low cost. In this work, in light of the photophysics of organic photodetector, a series of PDs responsing for different wavelengths are fabricated based on organic small molecule materials and their performance have been improved further.High efficiency deep ultraviolet organic photodetectors with spectral peak focusing on 280 nm is firstly demonstrated, using m-MTDATA to act as donor （D） material, Bphen as an acceptor （A） material and TPD as the light modulation and protection layer outside of the semitransparent Al cathode, respectively. The responsivity is 257.5mA/W at -8V under illumination of 280 nm with an intensity of 0.428 mW/cm². By using Cs2CO3 doped Bphen as electron transport layer, the responsivity of the device is improved to 309 mA/W with a detectivity of 1×10¹² cmHz1/2/W. The life time of the device is measured about 400 minutes under continuous illumination of 280 nm with an intensity of 0.18 mW/cm².High efficiency UV PD is reported using BAlq as the A material for its stronger UV absorption and higher electron mobility compared with Gaq.The responsivity is 514 mA/W at -7V under illumination of 365 nm UV light with an intensity of 1.2 mW/cm², 50% higher than that of the PD based on Gaq as A material reported by our group. In addition, taking LUMO and HOMO energy level and the radiation of exciple into account, the reason of good performance is analysed. The photocurrent of the unsealed photodiode decreases to 67% of its original intensity after 1000 min in room temperature and air environment under illumination of 365 nm UV light, showing the life time of the PD is much longer than 17 hours.High efficient UV PDs with energy transfer process are investigated based on 8-Hydroxyquinoline metal chelates （Beq, Mgq, Znq） as A material and m-MTDATA as D material, respectively.The responsivities are from 140-192 mA/W at -8V under illumination of 365 nm with an intensity of 1.2 mW/cm². It`s found that the radiation decay of A material is the main unwanted loss of the photogenerated carriers in the PDs.Taken the advantages of more flexible device design in using organic small molecule materials, a high efficient PD is demonstrated with broad spectral response and external quantum efficiencies of over 20% from 200 to 900 nm, a detectivity of 1×10¹² cmHz1/2/W and a fast response of 56 ns, using TiOPc as D material, and the blend of PTCDI-C8 and F16CuPc as the A material, respectively. The high performance is achieved by jointing two D/A hetero-junctions [m-MTDATA（D）/TiOPc（A） and TiOPc（D）/F16CuPc: PTCDI-C8（A）] and choosing D- and A-materials with matched energy level alignment and high carrier mobility. The high speed and deep-UV sensitivity might lead to potential military applications such as missile tracking in addition to optical communications, chemical/biological sensing etc.