New stable hole transport material for perovskite solar cells: Decaphenylcyclopentasilane polysilane material

Spiro-OMeTAD, currently the most widely used hole transport material, has high hole mobility. However, its poor thermal durability and low long-term stability when applied to photovoltaic devices are due to the moisture absorption and ion diffusion of the dopant. The objectives of this research are to fabricate and evaluate perovskite solar cells consisting of various perovskite compositions and stacked layered structures using decaphenylcyclopentasilane (DPPS), and to clarify the effects of DPPS on the perovskite layers. The novelty of this study is that bilayer stacked structures were fabricated using different types of perovskites using DPPS as a protective and hole transport layer, and to propose the design principles for highly reliable photovoltaic devices. Due to the high-temperature durability and chemical inertness of DPPS, high-temperature annealing of devices is possible, which is expected to improve the thermal stability and long-term stability of perovskite solar cells. Current–voltage measurements showed that devices using DPPS and heat-treated at higher temperatures than the ordinary annealing temperatures maintained their photoconversion efficiency even after one year. Thermal stability tests also showed that the devices maintainedefficiencies higher than 85% of their initial efficiencies after 3600 s at elevated temperatures. In addition, microstructure analysis through XRD measurements revealed that DPPS crystallized after the heat treatment. The results of optical absorption measurements showed that the crystallization of DPPS suppressed the desorption of MA⁺ from the perovskite, thereby increasing the optical absorption intensity, which indicated contribution to the improvement of the photoelectric conversion efficiencies of the devices.