Enhanced Efficiency of n‑i‑p Perovskite Solar Cells and Defect Passivation Using a Triphenylamine-Based Hole Transporting Interfacial Layer

The perovskite film surface and boundary defects are said to constitute nonradiative recombination and degradation sites, which limits the potential for perovskite solar cells’ (PSCs) long-term stability and power conversion efficiency (PCE). In order to overcome these limitations, herein we introduce a low-cost triphenylamine-based dopant-free molecule with a donor–acceptor–donor (D–A–D′) type structure, namely “TPA-ThA”, as a hole-transporting interfacial layer, which effectively passivates the perovskite surface defects and adjusts the energy level alignment between the perovskite/hole transport layer (spiro-OMeTAD). This passivator TPA-ThA, consisting of cyanopyridine as the acceptor core moiety and thiophene and triphenylamine as the donor units, was obtained by two-step synthetic methods without using the expensive catalyst and characterized spectroscopically. Further, strong compatibility with spiro-OMeTAD could result in the formation of a robust bilayer, which decreased the ion migration from the perovskite and effectively suppressed the moisture penetration toward the perovskite. Additionally, it has been shown that a conjugated ring merging into the molecular geometry is a useful method for enhancing the state of thermal stability, hole mobility, and charge extraction capability. Because of the better interface charge transfer/extraction and quality of perovskite films, we achieved a PCE of 14.65%, a short-circuit current density of 18.72 mA/cm2, an open-circuit voltage of 1.062 V, and a fill factor of 73.66% in the n-i-p structure composed of ITO/SnO2/perovskite/TPA-ThA/spiro-OMeTAD/Ag at the relative humidity of 70 ± 10%. As a result, the findings offer a viable approach to synthesize a hole-transporting interfacial layer compound for effective and long-lasting PSCs.