Perovskite solar cells have emerged as a promising photovoltaic technology due to their high power conversion efficiency, low-cost fabrication, and tunable optoelectronic properties. However, interfacial losses and non-radiative recombination at perovskite/charge transport layer interfaces remain critical challenges that limit device performance and stability. Nanomaterial-based interface engineering has proven effective in addressing these issues through tailored passivation strategies, work function modification, and precise energy level alignment.

One of the most significant sources of efficiency loss in perovskite solar cells is non-radiative recombination at interfaces, which arises from defects, trap states, and energy level misalignment. Quantum dots have been employed as interfacial modifiers to mitigate these losses. For instance, inorganic perovskite quantum dots such as CsPbBr3 have been used to passivate surface defects at the perovskite/hole transport layer interface. The quantum dots act as a protective layer, reducing interfacial recombination by filling halide vacancies and suppressing ion migration. Studies have demonstrated that quantum dot passivation can reduce trap density by over 50%, leading to enhanced open-circuit voltage and fill factor.

Polymer-based passivation layers offer another effective strategy for interface engineering. Conjugated polymers with functional groups such as carbonyl or amine can chemically interact with undercoordinated lead atoms on the perovskite surface, effectively passivating defects. Polymers like poly(methyl methacrylate) and polyethylenimine have been shown to form uniform interfacial layers that not only reduce recombination but also improve moisture resistance. These polymers can be processed via solution methods, making them compatible with large-scale fabrication. Devices incorporating polymer passivation layers have achieved open-circuit voltages exceeding 1.18 V, approaching the radiative limit for typical perovskite compositions.

Self-assembled monolayers (SAMs) provide atomic-level control over interfacial properties, enabling precise tuning of energy level alignment and work function. Phosphonic acid-based SAMs, such as [2-(9H-carbazol-9-yl)ethyl]phosphonic acid, have been used to modify the interface between perovskite and electron transport layers like SnO2. The SAMs form a dipole layer that shifts the work function of the underlying oxide, improving electron extraction while simultaneously passivating interfacial defects. This approach has resulted in devices with fill factors surpassing 83% and stabilized power conversion efficiencies over 24%.

Work function engineering is critical for minimizing energy losses at charge extraction interfaces. Nanomaterials such as metal oxides (MoO3, WO3) and conjugated polyelectrolytes have been employed to fine-tune the work function of charge transport layers. For example, ultrathin MoO3 interlayers deposited by atomic layer deposition can adjust the work function of the hole transport layer by up to 0.5 eV, facilitating better energy level matching with the perovskite absorber. This optimization reduces contact resistance and voltage losses, contributing to higher device performance.

Energy level alignment at interfaces is equally important for efficient charge extraction. Nanomaterials with tunable electronic properties, such as graphene oxide or transition metal dichalcogenides, have been integrated as interlayers to create favorable energy offsets. Recent work has demonstrated that a graded energy level alignment achieved through nanomaterial interlayers can reduce interfacial recombination currents by nearly an order of magnitude, leading to improved device efficiency.

Defect mitigation at interfaces is another key focus of nanomaterial-based engineering. Post-deposition treatments with molecules like phenethylammonium iodide or 2D perovskite layers have been shown to passivate both bulk and interfacial defects. These treatments form a thin, defect-free layer at the interface, significantly reducing non-radiative recombination centers. Advanced characterization techniques such as X-ray photoelectron spectroscopy (XPS) have revealed that these treatments effectively suppress the formation of lead clusters and halide vacancies, which are major contributors to recombination losses.

Characterization techniques play a crucial role in understanding and optimizing interfacial modifications. XPS provides chemical state information and reveals bonding interactions between passivation layers and perovskite surfaces. For instance, XPS studies have confirmed the binding of phosphonic acid SAMs to metal oxide substrates and their interaction with perovskite layers. Kelvin probe microscopy is another powerful tool for mapping work function variations and interfacial dipole effects at nanoscale resolution. These measurements have shown that optimized SAMs can induce work function shifts of up to 0.3 eV, directly correlating with improved device performance.

Recent breakthroughs in interface engineering have pushed perovskite solar cell efficiencies beyond 25%. A notable example involves the combination of 2D perovskite passivation layers with optimized charge transport materials, achieving certified efficiencies of 25.7%. Another advancement utilized a bilayer interface architecture comprising a polymer passivation layer and a quantum dot buffer, resulting in devices with both high efficiency and improved operational stability. These innovations demonstrate that nanomaterial-based interface engineering can simultaneously address multiple loss mechanisms in perovskite solar cells.

The stability of perovskite solar cells has also benefited from interfacial modifications. Nanomaterial passivation layers can act as barriers against moisture ingress and ion migration, two major degradation pathways. For example, hydrophobic quantum dot layers have been shown to increase device stability under damp heat testing, retaining over 90% of initial efficiency after 500 hours of exposure. Similarly, cross-linked polymer networks at interfaces have demonstrated enhanced mechanical robustness, reducing delamination and contact degradation during thermal cycling.

Future developments in nanomaterial interface engineering will likely focus on multifunctional designs that combine passivation, charge transport optimization, and stability enhancement in a single interlayer. The integration of machine learning approaches for material selection and interface design could further accelerate progress in this field. As understanding of nanoscale interfacial phenomena deepens, perovskite solar cells are expected to approach their theoretical efficiency limits while meeting commercial stability requirements.

In summary, nanomaterial-based interface engineering has become indispensable for advancing perovskite solar cell performance. Through quantum dot passivation, polymer interlayers, and self-assembled monolayers, researchers have made significant progress in reducing non-radiative recombination, tuning work functions, and aligning energy levels. Advanced characterization techniques have provided critical insights into these interfacial modifications, guiding the development of devices with record efficiencies. With continued innovation in nanomaterial design and interface control, perovskite photovoltaics are poised to play a major role in the future of renewable energy.