Wide optical gap B-doped nc-Si thin films with advanced crystallinity and conductivity on transparent flexible substrates for potential low-cost flexible electronics including nc-Si superstrate p–i–n solar cells

Abstract

The current boost in flexible energy harvesting devices demands the fabrication of solar cells on non-rigid, light-weight and cheap substrates to make roll-to-roll processing technology economically viable. Thus, herein, B-doped nc-Si films possessing ∼82.5% crystallinity with an average grain size of ∼9.63 nm, optical band gap of ∼1.836 eV and electrical conductivity of ∼2.02 S cm⁻¹ were grown from SiH₄ without deliberate H₂ dilution on optically transparent flexible PET substrates at around 30–100 °C. This process was facilitated by the inherent high electron density of the low-pressure plasma in the inductively coupled (ICP) plasma-CVD and strain-induced nanocrystallization process at the incubation layer, originating from substrate surface bending via plasma heating. It was observed that better compliance was achieved on the flexible PET substrate due to its surface deformation, which provided efficient intrinsic stress relaxation during the growth of the film network via energy transfer across the film-substrate interface, triggering prompt crystallization in the film network at a relatively low growth temperature compared to that on the glass substrate. Thus, these films are significant due to their suitable characteristics for the fabrication of low-cost flexible electronics and exclusively for use as window layers in nc-Si superstrate p–i–n solar cells even at ambient temperature.