Improved contact quality for silver-free silicon heterojunction solar cells by phosphoric acid treatment

•H3PO4 is used to modify the ITO surface for obtaining better wettability and higher work function.•The gird on the H3PO4-treated ITO is pinhole-free and more uniform.•After H3PO4 treatment, the contact resistivity between the electroplated grid and ITO is significantly reduced from 1.5 mΩ·cm2 to 0.4 mΩ·cm2.•The proof-of-concept SCs with H3PO4-treated ITO receives a champion power conversion efficiency of 23.19%.