Efficient charge separation and transport in a tandem solar cell with photoconducting Se sub-microtubes and AgBiS2 quantum dots

•p-type AgBiS2 quantum dots anchored to NiO function as an efficient photocathode.•Trigonal-Se sub-microtubes (t-Se s-μT) tethered to TiO2/CdS serve as the photoanode.•Hole- and photo- conductivity of t-Se s-μT impart a high efficiency to tandem cell.•TiO2/CdS/Se/S/S2−/SiO2 gel/AgBiS2/NiO cell delivers an efficiency of ∼ 6.9%.•Tandem cell sustains prolonged illumination with almost no degradation.