Modification of New Triphenylamine–Pyrimidine Derivatives Enables Improvement of All‐Inorganic CsPbI 3 Perovskite Solar‐Cell Properties

This study addresses the critical challenges of phase and defect instabilities in CsPbI 3 perovskite by employing interfacial modifiers based on triphenylamine‐pyrimidine, achieving a relative power conversion efficiency (PCE) boost of over 20%. CsPbI 3 perovskite, known for its ideal bandgap (≈1.7 eV), exceptional light absorption, excellent charge transport properties, and good thermal stability, has emerged as a promising photoactive material for next‐generation photovoltaics. However, its practical application is hindered by two major issues: a high defect‐state density and phase instability, both of which significantly limit the achievable PCE in solar cells. In this work, we overcome these challenges through innovative interface engineering using two newly designed triphenylamine–pyrimidine derivatives (TP‐CN and TP‐CF 3 ). This surface modification strategy yields two key benefits: a significant reduction in the defect‐state density of the photoactive layer and effective suppression of nonradiative charge carrier recombination. These improvements result in a remarkable enhancement of the PCE from a baseline of 12.57% to 15.32% (a 21.88% relative improvement) for TP‐CN‐modified devices and to 14.01% (an 11.46% relative improvement) for TP‐CF 3 ‐modified devices. The superior performance of TP‐CN, particularly in defect passivation and charge transport, underscores its potential as a versatile interface modifier for highly efficient CsPbI 3 perovskite solar cells.