Investigation on physical properties of solution-processed inorganic metal-oxides based charge extraction layers for 3G hybrid solar cells

Charge extraction layers, which include the hole extraction layer (HEL) and the electron extraction layer (EEL), are an essential component of a hybrid solar cell. In this work, charge extraction layers for hybrid solar cells have been fabricated from low-temperature solution-phase synthesis techniques by utilizing inexpensive and non-toxic inorganic metal-oxide semiconductors. Subsequently, the films have been optimized in terms of their various physical properties via microscopy based characterization techniques. Nanoparticles of zinc oxide and molybdenum trioxide have been synthesized by wet chemistry precipitation route at temperatures below 100C. X-ray Diffraction (XRD) analysis confirms high purity and hexagonal structure of the as-synthesized nanoparticles. Charge extraction layers were deposited by spincoating the colloidal suspension and initial study of film quality via optical microscopy indicated positive results for zinc oxide film. Nanoparticles of molybdenum trioxide, as opposed to zinc oxide, form larger aggregates during film deposition, hence resulting in poorer film quality in terms of coverage, adhesion and stability. Therefore, an alternate fabrication route is proposed for molybdenum trioxide film as the HEL to replace the conventionally used acidic and hygroscopic PEDOT:PSS polymer. For the EEL, the result of varying concentrations of colloidal dispersion on the surface morphology of the zinc oxide film on a nanoscale regime is analyzed through SEM studies. Finally, these optimized charge extraction layers are suitable for use in hybrid solar cells based on photoactive layer comprising of organic semiconductor P3HT.