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 long-term 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.