Enhanced photovoltaic output of bifacial perovskite solar cells via tailoring photoelectric balance in rear window layers with 1T-WS2 nanosheet engineering

Abstract

The development of high-quality rear window layers (RWLs) with excellent photoelectric properties is key to achieving a high photovoltaic (PV) output from bifacial perovskite solar cells (b-PSCs). Herein, we propose a novel strategy to improve the photoelectric balance of RWLs by introducing 1T-phase tungsten disulfide (1T-WS₂) nanosheets with metallic properties into a traditional organic hole-transporting layer (HTL) to create an organic–inorganic hybrid model. The mechanisms responsible for the synergistic improvement in the photoelectric and physical properties of the hybrid system, particularly the light-trapping capability, interface properties, charge dynamics, and PV parameters of the b-PSCs, are discussed in depth. The decrease in the thickness of the hybrid HTL due to the introduction of 1T-WS₂ not only enhances the optical transmittance, but also accelerates hole transfer in the improved system to a certain extent. Moreover, the decrease in the surface potential of the hybrid HTL driven by 1T-WS₂ improves the work function and brings the valence band closer to that of the perovskite. This energy-level alignment caused by Fermi level reduction effectively promotes hole extraction/transfer/collection and suppresses interface recombination, thus improving the PV parameters of devices. Owing to the fact that 1T-WS₂ doping synchronously enhances the light-harvesting capability and charge behavior of the device, the obtained maximum efficiencies of the optimized hybrid b-PSC under front and rear illuminations are 19.87 and 15.48%, respectively, which are superior to those of conventional organic b-PSCs. Ultimately, the 1T-WS₂-doped RWL created in this work effectively alleviates the PV degradation caused by water erosion and photo-thermal degradation of b-PSCs during environmental testing. The corresponding unencapsulated devices exhibit excellent irradiation/operational stability. This work provides important insights into the improvement in the photoelectric balance of RWLs in bifacial and tandem devices, and establishes a foundation for the widespread application of two-dimensional transition metal dichalcogenides in high-efficiency PV devices.