Fig. 2: Prerequisites and mechanism of the UV-induced thickness thinning effect.
From: Light-induced fine-tuning of optical cavities for organic optoelectronic devices
a Absorption peak shift of BF-DPB:NDP9 (10 wt.%, 150 nm) layer exposed to various UV wavelengths for 2 h in air within a Cr (3 nm) / Au (60 nm) / BF-DPB:NDP9 (10 wt.%, 150 nm) / Ag (25 nm) cavity structure. The absorption peak of samples without treatment (w/o) is also presented. BP and LP denote bandpass and longpass filters, respectively. b Absorption peak shift of different organic materials including BF-DPB:NDP9 (10 wt.%), alpha-NPD, TCTA, MeO-TPD, Spiro-TTB, TPBi, and C60 after 2 h UV irradiation in N2 and air atmosphere, compared to samples without treatment (dashed line). All samples are within a Cr (3 nm) / Au (60 nm) / organic layer (150 nm) / Ag (25 nm) cavity structure. c The N1s, (d) O1s, and (e) C1s peaks in XPS spectra of MeO-TPD (40 nm) on ITO substrates before and after 0.5 h UV irradiation. f Raman spectra of MeO-TPD (150 nm) w/o and after 0.5 h and 1.5 h of UV irradiation. g ATR-FTIR spectra of MeO-TPD w/o (49 nm film thickness) and after 0.5 h (33 nm film thickness) and 1.0 h (11 nm film thickness) of UV irradiation. FTIR spectra are normalized to the layer thickness. h Schematic illustration of UV-induced chemical reaction in MeO-TPD. Left: oxidative fragments and products by photo-oxidation and cross-reaction. Right: ether-linked dimers and tetramers by photo-induced oligomerization.
