Importance of passivation efficiency of the passivator for efficient printable mesoscopic perovskite solar cells

The stacking of multiple defect-rich grain boundaries (GBs) along the long transportation path (∼3 μm) of charge carriers in printable mesoscopic perovskite solar cells (p-MPSCs) impedes their power conversion efficiency (PCE). Organic Lewis bases are widely utilized for defect passivation at GBs, but how their passivation efficiency affects energy loss remains unclear. Here we employed triphenylphosphine (TPP) and triphenylphosphine oxide (TPPO) as the model passivators in p-MPSCs. TPPO has a more negatively charged center than TPP, which enables its stronger coordination with one of the most common and detrimental defects at the GBs—undercoordinated lead. When added into the perovskite with the same ratio, TPPO passivates defects more significantly and thus less TPPO remaining inactive compared with TPP. Inactive organic passivators accumulated at the GBs could impose barriers to charge carrier transportation. Indeed, TPPO improves the device performance more significantly with a champion PCE of 20.54% achieved. Besides, the TPPO devices demonstrate excellent stability with 95% of initial PCE remaining after 600 h of maximum power point tracking at (55 ± 5)°C.