Page - 3 - in Photovoltaic Materials and Electronic Devices

The devices were fabricated with an architecture of ITO/PEDOT:PSS/PTB7:PC71BM/LiF/Al. The indium tin oxide (ITO) glass substrates with a sheet resistance of 10 Ω/Sq were cleaned consecutively in ultrasonicbathscontainingglass lotion,ethanolandde-ionizedwatersequentially, and then dried by high pure nitrogen gas. The pre-cleaned ITO substrates were then treated by UV-ozone for 5 min for further cleaning the substrates and improving work function of the ITO substrates. The PEDOT: PSS (purchased from Clevios AI 4083) was spin-coated on the ITO substrates at 3000 rounds per minute (rpm) for 40 s. Then PEDOT: PSS coated ITO substrates were dried in air at 150 ˝C for 10 min. The substrates were then transferred to a nitrogen-filled glove box (<100 ppm O2 and <0.2 ppm H2O). On the other hand, in order to fabricate the differentdevices (without DIOadditive)asdesignedin experiment,0.5%,1%, 2.5% and 5% of PS by weight were added into PTB7/PC71BM mixed solution respectively onlyhalfanhourapart, andthentheactive layerswithdifferent ratiosofPSwere formed by spin-coating on the PEDOT: PSS with same spin-coating parameters, 1s foraccelerationand120s with the rotation speed of 1000 rpm. On the top of the active layer, a 0.7 nm interfacial layer LiF was evaporation deposited under 10´4 Pa vacuum conditions. The thickness of LiF was monitored by a quartz crystal microbalance. An aluminum cathode layer about 100 nm was then evaporation deposited on LiF layer under 10´4 Pa vacuum conditions in same deposition chamber with changed target. The active area was defined by the vertical overlap of ITO anode and Al cathode which is about 4 mm2. The light mask was not used duringI-Vmeasurement, andthepotential foredgeeffectsmayhaveaneffectonthe results. For theconvenienceofdiscussion,differentfilmsanddeviceswerenamed andpreparedtocompare theirperformances: Film1: PTB7:PC71BM, Film2: PTB7:PC71BM,1wt%PS Film3: PTB7:PC71BM,3v%DIO Film4: PTB7:PC71BM,1wt%PSand3v%DIO Device1: ITO/PEDOT:PSS/film1/LiF/Al Device2: ITO/PEDOT:PSS/film2/LiF/Al Device3: ITO/PEDOT:PSS/film3/LiF/Al Device4: ITO/PEDOT:PSS/film4/LiF/Al 2.2. PhotovoltaicCharacterization The absorption spectra of films were measured with a Shimadzu UV-3101 PC spectrometer. The thickness of the active layers is measured by an Ambios TechnologyXP-2stylusProfiler. ThethicknessesofFilm1,Film2,Film3andFilm 4 are 85 nm, 110 nm, 73 nm and 102 nm, respectively. The current–voltage (J-V) 3