DEPOSITION AND CHARACTERIZATION OF DOPAMINE AND POLYDOPAMINE THIN FILMS: MODIFIERS FOR ELECTRICAL CONTACTS IN PEROVSKITE SOLAR CELLS

Abstract

This work details the preparation and characterization of dopamine (Dop) and BOC-protected polydopamine (pDop) modification of TiO2 prepared by CVD as an interlayer for interfacial control of crystalline order and stability in mixed-halide formamidinium lead halide perovskites, an exciting light-harvesting material for thin-film photovoltaics. Dop and pDop modification is achieved by spin-coating from pH-adjusted aqueous solutions and rinsing with DMSO/DMF. Morphology of the films is studied by atomic force microscopy (AFM), showing conformal coating by pDop and preferential binding to chemically active TiO2 sites by Dop. The films are characterized by infrared reflection-absorption spectroscopy (IRRAS) and photoelectron spectroscopy (PES), and the surface energetics show a positive surface dipole and increased hole blocking capacity in pDop, both promising for a device interlayer. The effect of these modifications on perovskite growth, morphology, and crystallinity, is determined by X-ray diffraction (XRD) and AFM, showing an increase in perovskite crystallinity (due to surface passivation) on both Dop- and pDop-modified TiO2, and an unusual crystal orientation induced by pDop modification. A novel IR spectroscopic characterization of formamidinium in perovskite, probing disordered formamidinium at grain boundaries and crystalline domain interfaces is presented, improving on the current state of the literature.