Dual effective dopant based hole transport layer for stable and efficient perovskite solar cells

Conventionally, the hydroscopic nature of Li-TFSI and low boiling point of t-BP are considered as the primary limitations of hole transport layer (HTL), ultimately affecting the power conversion efficiency (PCE) and longterm stability of perovskite solar cell (PSC). To better stress these problems, a dual functional dopant termed PFPPY is reported. The in-depth operating mechanism of PFPPY with Spiro-OMeTAD, its profound effects on overall photovoltaic performance and device physics are systematically investigated. It is observed PFPPY can simultaneously take place of t-BP and FK209 in conventional HTL. By employing PFPPY as dopant cooperating with Spiro-OMeTAD, a higher PCE of 21.38% is achieved, compared with the reference device based on t-BP and FK209-doped Spiro-OMeTAD (19.69%). More importantly, the unencapsulated PFPPY-doped device shows greatly improved stability, maintaining over 90% of its initial PCE after 600 h in 40-50% RH. These findings provide a new strategy to optimize the HTL composition for efficient and stable PSCs.