Facile and sustainable interface modulation via a self-assembly phosphonate molecule for efficient and stable perovskite photovoltaics

Post-treatment has been demonstrated as an effective strategy for passivating defects, especially at interfaces, which detrimentally impede the photovoltaic performance of perovskite solar cells (PSCs). Herein, a self-assembly molecule with dipole moment, [4-(3,6-dimethyl-9H-carbazol-9-yl)butyl]phosphonic acid (Me-4PACz), is selected as an effective passivator to modulate the surficial environment of perovskite films by a facile solution method. The phosphonic groups of Me-4PACz can interact with uncoordinated Pb2+ to effectively reduce the surficial defect state density of perovskites and suppress nonradiative recombination. The introduction of self-assembled molecules between perovskites and spiro-OMeTAD not only forms negative dipoles pointing outward from the surface of perovskite, which leads to the improvement of the energy level alignment, but also possibly acts as a bridge for interfacial hole transfer, enhancing the efficiency of carrier extraction and transport. Consequently, after post-treatment via Me-4PACz, the power conversion efficiency (PCE) was boosted from 22.04 % to 23.29 % with decreased hysteresis. Meanwhile, the strong coordination effect of self-assembled molecules is also conducive to the device stability. The unsealed PSCs remained 84 % of initial efficiency after thermal aging at 85 °C for 504 h. This simple modification method using self-assembled molecules presents great potential for achieving stable and efficient PSCs based on sustainable passivation effect.