Acid-doped multi-wall carbon nanotube/n-Si heterojunctions for enhanced light harvesting

•The acid infiltration of the MWNT coatings can boost the MWNT/Si solar cell efficiencies by 12–19 times.•Nitric and sulfuric acid can significantly downshifts the Fermi level of MWNTs.•The infiltration of acid in the porous material forms MWNT-acid–Si photoelectrochemical units.•The acid treated MWNTs can reduce the internal series resistance by providing more charge transport paths.

Multiple wall carbon nanotube (MWNT) networks form Schottky-like heterojunction on n-type silicon substrate. Acid doping downshifts the Fermi level of the MWNTs, can significantly reduce the internal resistance of the MWNT film. Wetting the MWNT networks with nitric or sulfuric acid can form MWNT-acid–Si photoelectrochemical units. The photoelectrochemical units and the Si–MWNT heterojunctions connected in parallel on the same side of the Si substrate, consequently boosting the power conversion efficiency by more than 10 times.