Design of dendritic core carbazole-based hole transporting materials for efficient and stable hybrid perovskite solar cells

Designing organic molecules efficient for charge extraction and transport when integrated in optoelectronic devices remains a great challenge for many advanced applications. In perovskite solar cells (PSCs), the hole extraction/transport and the device stability are strongly dependent on the molecular structure of the hole transporting material (HTM). Herein we have engineered a dendritic core carbazole based HTM (named B186), which combines the advantages of both small molecules and polymeric materials. The material can be easily prepared in a short synthetic procedure from largely available commercial products. We have investigated in-depth the relationship between the chemical structure of the HTM and both the photovoltaic efficiency and the device stability. It has been shown that the dendritic core is a promising approach leading to both enhanced device performance and stability. The new HTM has been proved to act as a good barrier and protect satisfactorily the perovskite surface. The power conversion efficiencies (PCE) increase from 11.5% for the simple model compound to a promising 14.6%. Additionally, the normalized PCE of B186-based PSC decreased by only 5% after more than three weeks of storage under ambient conditions meanwhile the cell using the most popular HTM (Spiro-OMeTAD) dropped off by more than 40%. The presented results demonstrate that introducing dendritic concept is a simple strategy to design HTM for efficient and stable PSC.