Physics

Ionic liquid

Relative humidity

Organic chemistry

Dopant

Energy conversion efficiency

Humidity

Engineering

Perovskite (structure)

Conductivity

Catalysis

Moisture

Physical chemistry

Composite material

Chemistry

Materials science

Hexafluorophosphate

Chemical engineering

Optoelectronics

Doping

Thermodynamics

ACS Sustainable Chemistry & Engineering

High-performance perovskite solar cells (PSCs) are readily degradable by moisture, leading to high demand for a water-repelling efficient hole transport layer (HTL). In this study, we proposed an anion-exchange approach to replace the conventional hygroscopic dopant anion─bis(trifluoromethanesulfonyl)imide (TFSI–)─with a hydrophobic dopant anion capable of effectively doping into a 2,2′,7,7′-tetrakis(N,N-di-p-methoxyphenylamine)-9,9′-spirobifluorene (spiro-OMeTAD) matrix. By varying the size of dopant anions, we successfully controlled electrostatic interactions between spiro-OMeTAD and the dopant anion. Hexafluorophosphate (PF6–) demonstrated the highest p-doping anion-exchange capability because the optimal-sized PF6– enabled a strong electrostatic interaction between spiro-OMeTAD•+ and PF6– while resulting in poor affinity between Li+ and PF6–. The resulting PF6–-doped spiro-OMeTAD HTL not only produced favorable energy band alignment with perovskite but also improved film conductivity. Correspondingly, the PSCs based on the PF6–-doped HTL exhibited a higher power conversion efficiency (PCE) of 20.78% than the reference TFSI–-based PSCs of 19.04%. Besides device performance, the superior hydrophobic nature of PF6– enabled the HTL to prevent water penetration into the perovskite layer, improving long-term stability against moisture. The PF6–-based PSCs exhibited enhanced humidity stability while maintaining 92% of the initial PCE for 1180 h at a relative humidity of 25% under ambient conditions.

Understanding the Influence of Anion Exchange on the Hole Transport Layer for Efficient and Humidity-Stable Perovskite Solar Cells