Efficient and Stable Vacuum-Free-Processed Perovskite Solar Cells Enabled by a Robust Solution-Processed Hole Transport Layer

Here, efficient and stable vacuum-free processed perovskite solar cells (PSCs) are demonstrated by employing solutionprocessed molybdenum tris-[1-(trifluoroethanoyl)-2-(trifluoromethyl)ethane-1,2-dithiolene] (Mo(tfd-COCF₃ )₃ )-doped poly(3,4-ethylenedioxythiophene) (PEDOT) film as hole transport layer (HTL). Our results indicate that the incorporation of Mo(tfd-COCF₃ )₃ dopant can induce p-doping through charge transfer from the highest occupied molecular orbital (HOMO) level of the PEDOT host to the electron affinity of Mo(tfd-COCF₃ )₃ , leading to an increase in conductivity by more than three orders of magnitude. With this newly developed p-doped film as HTL in planar heterojunction PSCs, a high power conversion efficiency (PCE) up to 18.47 % can be achieved, which exceeds that of the device with commonly used HTL 2,2',7,7'-tetrakis(N,N-di-p-methoxyphenyl-amine)9,9'-spirobifluorene (spiro-OMeTAD). Taking the advantage of the high conductivity of this doped film, a prominent PCE as high as 15.58 % is also demonstrated even when a large HTL thickness of 220 nm is used. Importantly, the high quality film of this HTL is capable of acting as an effective passivation layer to keep the underlying perovskite layer intact during solution-processed Ag-nanoparticles layer deposition. The resulting vacuum-free PSCs deliver an impressive PCE of 14.81 %, which represents the highest performance ever reported for vacuum-free PSCs. Furthermore, the resulting devices show good ambient stability without encapsulation.