Tungstite nanoparticles prepared by microwave-assisted synthesis and their application as a hole transporting layer in organic solar cells

Abstract

Thin films of tungstite (WO₃·H₂O) nanoparticles have been used as a hole transporting layer (HTL) in organic solar cells and demonstrated good performances. The nanoparticles were synthesized by dissolving WCl₆ in benzyl alcohol and using microwave-assisted heating at 130 °C and ambient pressure. The obtained nanoparticles exhibit a platelet form whose lateral size can be tuned from 30 nm to 250 nm by modifying the metallic salt concentration in solution. These particles were dispersed in an ethanol solution allowing the formation of homogeneous thin films with a relatively low roughness and a suitable work function (5.0 eV). The films were tested as a hole transporting layer in polymer solar cells in a standard structure with P3HT:PCBM as the active layer. A good V_OC has been observed due to a suitable energy level alignment and an average power conversion efficiency of 3.2% has been achieved with a best PCE of 3.49%. Moreover, an annealing treatment was not required to obtain a good photovoltaic performance (PCE = 3.1%). This represents a gain in cost and time in the device fabrication compared to post-deposition treated films obtained by the sol–gel method.