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

• p-type AgBiS 2 quantum dots anchored to NiO function as an efficient photocathode. • Trigonal-Se sub-microtubes (t-Se s-μT) tethered to TiO 2 /CdS serve as the photoanode. • Hole- and photo- conductivity of t-Se s-μT impart a high efficiency to tandem cell. • TiO 2 /CdS/Se/S/S 2− /SiO 2 gel/AgBiS 2 /NiO cell delivers an efficiency of ∼ 6.9%. • Tandem cell sustains prolonged illumination with almost no degradation. This article describes a tandem photoelectrochemical cell that captures and converts visible to near infrared light to deliver a power conversion efficiency of ∼ 7%. In this tandem device the photocathode was prepared from p-type nickel oxide sensitized with silver bismuth sulfide (AgBiS 2 ) quantum dots and was paired with a photoanode based on cadmium sulfide-sensitized titania. Trigonal-selenium sub-microtubes (t-Se s-μT) were anchored to the photoanode and served two roles: (1) enhancement of the conductivity under illumination (with holes as majority carriers); (2) co-sensitization provided more electron-hole pairs that increased the device performance by 1.5-fold. The separate p-type (AgBiS 2 /NiO−Ni) and n-type (TiO 2 /CdS/Se−Ni) solar cells were characterized as well as the (p/n) tandem cell architecture with a quasi-solid polysulfide/silica gel electrolyte under 1 sun illumination (AM 1.5G). The results provide scientific insights into the proposed charge flow mechanism via favourable energy level alignment in this unique device.