Influence Of Alkali Metal Compound Dopants On Electronic Structures Of Organic Semiconductors

Recently, Organic photoelectric device, such as organic electroluminescent device（OLED）, organic photovoltaic （OPV） and organic thin film transistor （OTFT）, haveattracted significant attention in academics and industries due to their potentialapplication in flat-panel and flexible display, information transport and storage,solid-state lighting, new generation energy, photocatalyst and so on. The study oforganic photoelectric device is benefit torealizing its commercialization. However, thereare still many scientific and technical problems remaining to be solved in organicoptoelectronics, such as instability, low efficiency, short life time, immaturemechanisms and so on.In this thesis, the work mechnisms of alkali metal compounds as an n-type dopantin organic electron-transport layers （ETLs） were studied via ultraviolet and X-rayphotoemission spectroscopies （UPS and XPS）. The mechnisms of charge transport ofthese materials were investigated by cryogenic probe station with a Keithley4200-SCSsemiconductor parameter analyzer. The details of research work are as following:⑴Influence of cesium carbonate dopants on electronic structures of BPhenFirstly，the working mechanisms of Cs₂CO₃as an n-type dopant in organicelectron-transport layer （BPhen） are studied via UPS and XPS. It is verified that Cs₂CO₃in the doped BPhen is partially decomposed into Cs₂O during thermal evaporation,without significant chemical reaction. The mechanisms of electron transportenhancement for Cs₂CO₃doped BPhen films are studied by cryogenic probe station witha Keithley4200-SCS semiconductor parameter analyzer. We also study the performanceof the OLED using Cs₂CO₃as an n-type dopant.⑵Influence of cesium azide dopants on electronic structures of organicsemiconductorsThe doping effect of CsN₃as an n-type dopant in electron transport materials（ETMs） are studied via UPS and XPS. It is verified that CsN₃in the doped ETMs （such as BPhen, Alq₃and so on） is fully decomposed into Cs during thermal evaporation, andobvious chemical reaction happens between CsN₃and ETM. The mechanisms ofelectron transport enhancement for CsN₃doped BPhen films are studied by cryogenicprobe station with a Keithley4200-SCS semiconductor parameter analyzer.⑶Influence of lithium nitride dopants on electronic structures of BPhenFinally, the working mechanisms of Li₃N as an n-type dopant in BPhen films arestudied via UPS and XPS. It is verified that Li₃N in the doped BPhen films is fullydecomposed into Li during thermal evaporation, and obvious chemical reaction occursbetween Li₃N and BPhen films.