Publication date: 5th November 2025
Perovskite solar cells (PSCs) utilizing poly[bis(4-phenyl)(2,4,6-trimethylphenyl)amine (PTAA) as hole-transport materials (HTMs) in n-i-p structures have promising thermal stability compared with those employing spiro-OMeTAD, which is the most widely used HTM. However, PTAA-based PSCs often exhibit lower efficiencies than spiro-OMeTAD-based ones, presumably due to the absence of perovskite passivation techniques suitably combined with PTAA HTMs. In terms of perovskite passivators, phenylalkylammonium (PRA)-based passivator is one of the most major categories as it is effective in improving PSC performances taking advantages of its large adsorption energy over perovskite surface. However, the conventional PEA-based passivation suffers from thermal stability issues. In the case of phenylethylammonium (PEA), for instance, the conventional PEA-based passivation suffers from thermal stability issues; under thermal stress even at moderate temperatures for a short duration (e.g., 50 °C for several minutes), the overlayer of the perovskite passivated with PEA iodide transforms to a two-dimensional (2D) perovskite of (PEA)2PbI4 (n = 1), which hampers carrier transfer, thus negating the passivation effects. [1]
Herein, we propose a simple strategy to address the thermal stability issues using PRA-bis(trifluoromethylsulfonyl)imide (PRA-TFSI) additives for PTAA HTM.[2] [3] During the HTM deposition with the PRA-TFSI additive over perovskite layers, the PRA cations spontaneously passivated the perovskite presumably exploiting the large adsorption energy, forming a monolayer-like passivation overlayer.[4] The resulting PRA-based passivation did not exhibit crystallization to the detrimental 2D perovskite at 85 °C; hence, it did not cause PV performance drop due to the thermal stress. The PSCs with optimal PRA-TFSI addition resulted in effectively enhanced PV performances, achieving a 23.2% power conversion efficiency. The PV performance enhancement can be attributed to both the improved affinity at the PTAA/perovskite interface, which is crucial in combining PTAA HTMs yet hardly attainable by aliphatic-ammonium-based passivators, and the PRA passivation effects. This study provides novel insights into widely used PRA-based passivators and paves the way for perovskite passivation effectively combined with thermally stable PTAA HTMs.
This work was supported by the project JPNP21016, commissioned by the New Energy and Industrial Technology Development Organization (NEDO).
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