Low temperature processable crystalline WO3 langmuir-blodgett ultra-thin film as blocking layer in solar cells application

A key to achieve high efficiency in solar cells is to have charge extraction layer with proper energy levels. This layer selectively extracts electrons (or holes) whilst blocking the hole (or electron) and therefore help in reducing the recombination at various interfaces. Conventionally, WO<inf>3</inf> is used as a hole-transport and electron-blocking layer in perovskite and polymer solar cells owing to high work function and carrier mobility and excellent thermal stability. In this paper, we report preparation of crystalline ultra-thin WO<inf>3</inf> films at low temperature and its application as electron-transport and hole blocking layer (BL). For this purpose, WO<inf>3</inf>-octadecyl amine (ODA) multilayers were prepared by Langmuir-Blodgett (LB) technique and decomposed by UV-ozone treatment. The films were annealed at different temperatures in order to improve the crystallinity. The conversion of WO<inf>3</inf>-ODA complex (WO<inf>3-ODA</inf>) in WO<inf>3</inf> was confirmed from X-ray photoelectron spectroscopy (XPS), Fourier Transform infrared spectroscopy (FTIR) and Raman spectroscopy. Films were further characterized using electrochemical technique in order to assess their blocking properties. Excellent blocking behavior observed for prepared WO<inf>3</inf> films suggest their suitability as BL in solar cell application. The WO<inf>3</inf> films, when employed as BL in dye sensitized solar cells (DSSC), were found to improve efficiency as well as short-circuit current density (Jsc) and open-circuit potential (Voc) in comparison with DSSCs fabricated using conventionally prepared TiO<inf>2</inf> BL. The analyses of obtained results suggest that the WO<inf>3</inf> film prepared by LB technique can be a potential blocking layer for DSSC and perovskite solar cells.