Band gap engineered ternary semiconductor Pb x Cd 1 −x S: Nanoparticle‐sensitized solar cells with an efficiency of 8.5% under 1% sun—A combined theoretical and experimental study

We report the synthesis and photovoltaic properties of a ternary metal sulfide alloyed semiconductor Pb x Cd 1 −x S prepared by the two‐stage sequential ionic layer adsorption reaction. The synthesized Pb x Cd 1 −x S nanoparticles (NPs) retain the hexagonal structure of the CdS host with Pb substituting a fraction of the Cd atom ( x = 0‐0.17). Band structures of Pb x Cd 1 −x S with various Pb contents x were calculated using the complementary density functional theory (DFT) method. Optical, quantum efficiency, cyclic voltammetry measurements, and band structure calculation revealed that the band gap of Pb x Cd 1 −x S decreased with increasing x , resulting in an increased optical absorption band from 500 to 720 nm (1.73‐2.44 eV) for x = 0 to 0.17. Solid‐state Pb x Cd 1 −x S semiconductor nanoparticle‐sensitized solar cells (NSSCs) were fabricated from the synthesized NPs using spiro‐OMeTAD as the hole‐transporting material. The best Pb 0.05 Cd 0.95 S cell yielded a power conversion efficiency (PCE) of 3.67%, a V oc of 0.70 V, and a fill factor (FF) of 62.8% under 1 sun. The PCE increased to 5.93% under a reduced light intensity of 0.1 sun and further increased to 8.48% under 0.01 sun. The external quantum efficiency (EQE) spectrum covers the spectral range of 300 to 730 nm with a maximal EQE of 82% at λ = 580 nm. The PCE over 8% can be categorized into a high‐efficiency NSSCs. In addition, the V oc of 0.70 V is a relatively high V oc among all NSSCs. The high PCE and V oc suggest that Pb x Cd 1 −x S has potential to be an efficient solar absorber.