Abstract
We report that UV–ozone treatment of TiO2 anatase thin films is an efficient method to increase the conductance through the film by more than 2 orders of magnitude. The increase in conductance is quantified via conductive scanning force microscopy on freshly annealed and UV–ozone-treated TiO2 anatase thin films on fluorine-doped tin oxide substrates. The increased conductance of TiO2 anatase thin films results in a 2% increase of the average power conversion efficiency (PCE) of methylammonium lead iodide-based perovskite solar cells. PCE values up to 19.5% for mesoporous solar cells are realized. The additional UV–ozone treatment results in a reduced number of oxygen vacancies at the surface, inferred from X-ray photoelectron spectroscopy. These oxygen vacancies at the surface act as charge carrier traps and hinder charge extraction from the adjacent material. Terahertz measurements indicate only minor changes of the bulk conductance, which underlines the importance of UV–ozone treatment to control surface-based defects.
Highlights
Thin films of anatase titanium dioxide (TiO2) are applied in electronics ranging from thin film transistors, and anode materials for lithium-ion batteries, to memristors and photoanodes for water oxidation.[1−5] For all these electronic devices, a careful adjustment of oxygen vacancies and a reproducible electrical resistance of TiO2 play a major role.[6]
We report that UV−ozone treatment of TiO2 anatase thin films is an efficient method to increase the conductance through the film by more than 2 orders of magnitude
UV− ozone-treated TiO2 anatase thin films resulted in an increase of two percentage points of the average power conversion efficiency (PCE) of solar cells, reaching values up to 19.5%
Summary
Thin films of anatase titanium dioxide (TiO2) are applied in electronics ranging from thin film transistors, and anode materials for lithium-ion batteries, to memristors and photoanodes for water oxidation.[1−5] For all these electronic devices, a careful adjustment of oxygen vacancies and a reproducible electrical resistance of TiO2 play a major role.[6]. UV− ozone-treated TiO2 anatase thin films resulted in an increase of two percentage points of the average power conversion efficiency (PCE) of solar cells, reaching values up to 19.5%. TiO2 anatase readily forms smooth and pinhole-free films that enable efficient electron extraction with a PCE of over 23% for mixed-cation-based perovskite solar cells.[14] during the preparation of TiO2 films for PSC, oxygen vacancies in bulk and at surfaces can be formed.[15]. After 30 min of UV−ozone treatment, the median current through the TiO2 layer increased by 2 orders of magnitude This increased conductance is accompanied by a decreased number of surface oxygen vacancies, which was evidenced by XPS. We studied the influence of UV−ozone treatment on the bulk conductance of TiO2 films by THz spectroscopy This optical pump THz probe setup was driven by an amplified laser system (Solstice ACE by Spectra-Physics).
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