Binary hole transport layer enables stable perovskite solar cells with PCE exceeding 24%

Hygroscopic dopant in hole transport layer (HTL) is a key factor contributing to moisture-induced perovskite degradation and the resulting performance loss over time. This poses obstacles to the commercialization of perovskite solar cells (PSCs). Herein, we mixed two popular hole transport materials, i.e., [2,2′,7,7′-tetrakis(N,N-di-p-methoxyphenyl-amine)9,9′-spirobifluorene] (Spiro-OMeTAD) and poly (3-hexylthiophene-2,5-diyl) (P3HT), to form a binary mixed HTL. Due to the presence of hydrophobic P3HT component, the mixed HTL exhibits improved moisture resistance. In addition, P3HT demonstrates a great ability to interact with the dopants, which changes π-π packing orientation of P3HT from edge-on to face-on and improves its crystallinity, thus increasing hole mobility and hole extraction capability of the mixed HTL. As a result, PSCs equipped with the Spiro-OMeTAD/P3HT mixed HTL exhibit a champion power conversion efficiency (PCE) up to 24.3% and superior operational stability. The cells without encapsulation can maintain 90% initial efficiency after storage in dark ambient conditions (30% RH) for 1200 ​h. These results suggest that constructing Spiro-OMeTAD/P3HT mixed HTL is a promising strategy to meet the future photovoltaic applications demands with low-cost as well as excellent efficiency and device stability.