penghuang

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.

No vacuum needed: We report the use of a solution-processed Mo(tfd-COCF₃)₃-doped PEDOT film as hole transport layer for achieving high-performance and stable hybrid perovskite solar cells prepared by vacuum-free processing.

It is well known that the surface trap states and electronic disorders in the solution-processed CH₃NH₃PbI₃ perovskite film affect the solar cell performance significantly and moisture sensitivity of photoactive perovskite material limits its practical applications. Herein, we show the surface modification of a perovskite film with a solution-processable hydrophobic polymer (poly(4-vinylpyridine), PVP), which passivates the undercoordinated lead (Pb) atoms (on the surface of perovskite) by its pyridine Lewis base side chains and thereby eliminates surface-trap states and non-radiative recombination. Moreover, it acts as an electron barrier between the perovskite and hole-transport layer (HTL) to reduce interfacial charge recombination, which led to improvement in open-circuit voltage (V_oc) by 120 to 160 mV whereas the standard cell fabricated in same conditions showed V_oc as low as 0.9 V owing to dominating interfacial recombination processes. Consequently, the power conversion efficiency (PCE) increased by 3 to 5 % in the polymer-modified devices (PCE=15 %) with V_oc more than 1.05 V and hysteresis-less J–V curves. Advantageously, hydrophobicity of the polymer chain was found to protect the perovskite surface from moisture and improved stability of the non-encapsulated cells, which retained their device performance up to 30 days of exposure to open atmosphere (50 % humidity).

Moisture and charge barrier: We show the surface modification of a perovskite film with a solution-processable hydrophobic polymer (poly(4-vinylpyridine), PVP), which passivates the undercoordinated lead atoms (on the surface of perovskite) by its pyridine Lewis base side chains and eliminates surface-trap states and non-radiative recombination, and acts as an electron barrier between the perovskite and hole-transport layer.