Small molecule with substantial latent heat of vaporization and distribution coefficient facilitates improved device performance in p-i-n perovskite solar cells

The existence of imperfections and defects on the perovskite absorber surface causes charge carrier trapping, interfacial non-radiative recombination, and inefficient charge extraction, resulting in a pronounced hysteresis and not-so-ideal device performance. To scale down the hysteresis, it is pivotal to minimize the detrimental surface defects. Keeping this in mind, amylamine, a lower aliphatic amine possessing a higher distribution coefficient, was employed as a screening layer on top of the perovskite absorber. Due to its higher enthalpy of vaporization ΔHvap and strong Lewis base character, it effectively passivates the surface defects in the absorber film by forming a stronger Lewis acid-base adduct. Also, it acts as a thermodynamically stable material for passivation through intermolecular interaction. X-ray photoelectron spectroscopy analysis reveals a shift in Pb2+ binding energy, confirming that the amylamine molecule is involved in the passivation of the perovskite absorber's undercoordinated Pb2+ defects. Also, the amine passivated absorber film shows an enhanced photoluminescence (PL) intensity and improved charge carrier lifetime due to suppressed non-radiative recombination. Lower hysteresis index (HI) and reduced theoretical Voc loss were observed for the passivated device. When measured in high relative humidity (RH ∼65–70%) conditions, the optimized unencapsulated device showed a power conversion efficiency (PCE) of 15.43% with an open circuit voltage of 1.031 V, whereas the PCE of the pristine device was 11.82%. This work demonstrates that the simple small molecule reduces the recombination and defect-induced charge carrier trapping at the absorber/charge selective layer interface, which results in an improved device performance in planar p-i-n perovskite solar cells.