Researchers explored the internal characteristics of affordable materials used in perovskite solar cells, which are gaining popularity due to their impressive efficiency. They utilized electron spin resonance (ESR) to study these materials at a microscopic level. Their findings shed light on the reasons behind poor device performance, even with high local charge mobility, providing essential information for the development of better solar cells.
Researchers from the University of Tsukuba have looked into the inner attributes of low-cost materials utilized in perovskite solar cells, known for their high efficiency, using electron spin resonance (ESR) for microscopic analysis. Their results reveal the reasons for decreased device efficiency, despite having high local charge mobility, and offer valuable insights for creating improved solar cells.
Perovskite solar cells are gaining traction as a promising solar technology due to their exceptional ability to convert light into electricity. However, a widely used hole-transport material, 2,2′,7,7′-tetrakis(N,N-di-p-methoxyphenylamine)-9,9′-spirobifluorene (spiro-OMeTAD), comes with drawbacks, including a complicated synthesis process and high costs. To overcome these challenges, researchers have created N3,N3,N11,N11-tetrakis(4-methoxyphenyl)[1,4]benzoxazino[2,3,4-kl]phenoxazine-3,11-diamine (HND-2NOMe), which is an economical and easily synthesized hole-transport material. HND-2NOMe molecules feature a quasi-planar structure that allows for one-dimensional overlapping alignment, enhancing charge transfer. Despite showing high charge mobility, perovskite solar cells with HND-2NOMe still face performance issues, including lower current, the reasons for which have yet to be clarified.
To uncover the mechanisms behind these performance issues, researchers at the University of Tsukuba applied ESR to examine the internal properties of perovskite solar cells using HND-2NOMe. Their investigation revealed that, without light, holes move from the perovskite to HND-2NOMe, creating an energy barrier at the interface that hinders the flow of holes and contributes to the observed performance limitations. Additionally, these solar cells showed diminished hole accumulation when exposed to sunlight, which affects the stability of hole transport capabilities.
Understanding the reasons for these performance challenges while preserving functional stability is a significant step forward, with crucial implications for developing guidelines to improve device performance. Furthermore, these insights will provide a solid foundation for future research and advancements in perovskite solar cell technology.
