The hole transport polymer poly (3,4-ethylenedioxythiophene):poly(4-styrenesulfonate) (PEDOT:PSS) derives many of its favorable properties from a PSS-rich interfacial layer that forms spontaneously during coating. Since PEDOT:PSS is only usable as a blend it is not possible to study PEDOT:PSS without this interfacial layer. Through the use of the self-doped polymer sulfonated poly(thiophene-3-[2-(2-methoxyethoxy) ethoxy]-2,5-diyl) (S-P3MEET) and a polyfluorinated ionomer (PFI) it is possible to compare transparent conducting organic films with and without interfacial layers and to understand their function. Using neutron reflectometry, we show that PFI preferentially segregates at the top surface of the film during coating and forms a thermally-stable surface layer. Because of this distribution we find that even small amounts of PFI increase the electron work function of the hole transport layer. We also find that annealing at 150 C and above reduces the work function compared to samples heated at lower temperatures. Using near edge X-ray absorption fine structure spectroscopy and gas chromatography we show that this reduction in work function is due to S-P3MEET being doped by PFI. Organic photovoltaic devices with S-P3MEET/PFI hole transport layers yield higher power conversion efficiency than devices with pure S-P3MEET or PEDOT:PSS hole transport layers. Additionally, devices with a doped interface layer of S-P3MEET/PFI show superior performance to those with un-doped S-P3MEET.
In this work, polycrystalline silicon (poly‐Si) thin films were fabricated by aluminum induced crystallization (AIC) technique. SiNx, deposited as a function of NH3/SiH4 ratio, and AZO (Al‐doped ZnO) films on glass were used as a buffer layer between glass and Si film. The effect of buffer layer content on the crystallinity of poly‐Si thin films was studied by Raman analysis which shows that fully crystallization without stress was achieved for all samples. Moreover, the preferred crystalline orientation and crystallite size of films were deduced by X‐ray diffraction (XRD) analysis. The preferred orientation is <100> as independent from the buffer layer content while the crystallite sizes increase up to 48.5 nm by increasing the amount of SiH4. The electrical properties of the films were carried out by four point probe and current–voltage (I–V) analysis. Both techniques demonstrated that the resistivity of the SiNx‐based samples is around 0.1 Ωcm. The grain size analysis was accomplished by electron back scattering diffraction (EBSD) measurements. The grain size up to 25 µm was achieved as observed from EBSD images. The results show that the fabrication parameters of SiNx and AZO buffer layers have the great effects on the crystallography of poly‐Si films.
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