Interface Engineering for Efficient and Stable NiO_x-Based Inverted Perovskite Solar Cells

Organic-inorganic hybrid perovskite solar cells (PSCs) have emerged as a burgeoning paradigm in the realm of photovoltaic technologies. Within this domain, a great research endeavour has been channelled toward the exploration of hole transport materials (HTMs) for inverted PSC architectures. Among these, nickel oxide (NiO_x) has garnered widespread adoption, owing to its constellation of virtues, including straightforward synthesis, facile processing, elevated optical transparency, and superlative chemical robustness. Despite the encouraging strides made with inverted PSCs in recent years, the photovoltaic conversion efficiencies (PCEs) achieved by NiO_x alone far remain eclipsed by those achieved using high-performance organic HTMs. This discrepancy is ascribed to the incongruent energy levels, the intrinsic low electrical conductivity, and the heightened interface defect density associated with NiO_x. Additionally, the NiO_x layer is often beset by a complex assortment of high-oxidation-state nickel species (Ni^&gt;³⁺), which convolute its surface chemistry and precipitate the deterioration of perovskite materials.<br/><br/>In an endeavour to surmount these challenges, we reveal the origin of open-circuit voltages (<i>V</i>_OC) loss in NiO_x-based tin PSCs and the influencing mechanism of hole-extraction barrier formation at the NiO_x-perovskite interface due to Sn oxidation. Specifically, the undercoordinated Ni^≥3+ defects act as Lewis acids and oxidants on divalent Sn ions with low oxidation activity energy at the buried interface. To address this issue, we introduced a novel self-assembled monolayer (SAM), (4-(7H-dibenzo[c,g]carbazol-7-yl)ethyl)phosphonic acid (2PADBC), as an interfacial modification layer between perovskite and NiO_x. Passivation of reactive Ni^≥3+ defects yield a significantly increased <i>V</i>_OC from 0.712 V to 0.825 V, boosting the PCE to a champion 14.19% for small-area devices and a 12.05% for large-area (1cm²) devices. Furthermore, the 2PADBC modification improved the operational stability of NiO_x-based tin PSCs, which maintains over 93% of their initial efficiency after 1000 hours.<br/><br/>Furthermore, we have adeptly engineered and synthesized a novel donor-acceptor (D-A) type semiconductor, denoted as BTF14, which is predicated upon a fluoranthene imide scaffold. This semiconductor can serve as a multifunctional interfacial material, poised to enhance the performance of NiO_x-based inverted PSCs. By integrating BTF14 into the device architecture, we have facilitated improved charge transfer kinetics, augmented the crystalline quality of the perovskite film, and substantially mitigated defect density at the perovskite/NiO_x interface. Consequently, this integration has culminated in a remarkable elevation of the PCE to 24.20%, accompanied by an imperceptible presence of hysteresis. Furthermore, BTF14 has demonstrated an adeptness at diminishing the concentration of deleterious Ni^&gt;³⁺ species on the NiO_x surface. It also fosters robust interfacial interactions between the NiOx and the perovskite layers, thereby bolstering the operational stability of the device. Impressively, more than 77% of the initial PCE was retained after 1000 hours of continuous operation at an ambient temperature of 60°C.