A 14.7% Organic/Silicon Nanoholes Hybrid Solar Cell via Interfacial Engineering by Solution-Processed Inorganic...

We demonstrated a high-performance Si-organic hybrid heterojunction solar cell utilizing low-temperature and liquid-phase-processed TiO₂ as an interlayer between poly(3,4-ethylene dioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) and Si nanoholes to produce a conformal contact on the surface of the Si nanostructure. The hydrophilic TiO₂/Si-nanohole surface enabled the PEDOT:PSS to flow into the spacing of the close-packed nanoholes. Scanning electron microscopy images were used to confirm the PEDOT:PSS nanohole filling induced by the TiO₂. With forming gas annealing of the double-sided TiO₂, high V_oc (0.63 V) and J_sc (35.7 mA/cm²) values were obtained, yielding a high power conversion efficiency of 14.7%. The high V_oc was attributed to the surface passivation of Si by annealed TiO₂. The X-ray photoelectron spectroscopy investigation at the TiO₂/Si interface indicates the TiO_x signal decreased and the TiO₂ and SiO_x signals increased after annealing. The Si-O bonding found in the O 1s study appeared in the form of Si-O-Si bonding to serve surface passivation. The band alignment of the PEDOT:PSS/TiO₂/n-Si hetero-interfaces was postulated and plotted. The V_bi in the system after annealing was assumed to be higher because of the reduction of bulk and surface states that yield high V_oc. After annealing, the V_bi increased from 0.805 to 0.905 V. The reduction of surface recombination velocity proved the passivation ability of TiO₂ after annealing. With proven surface passivation and conformal PEDOT:PSS/Si nanohole interfaces for enhanced contact, this Si-organic hybrid heterojunction solar cell with solution-processed TiO₂ interlayers has excellent potential for application as a high-efficiency and low-cost Si solar cell.