Perovskite quantum dot-sensitized solar cells (PQDSCs) represent a promising advancement in photovoltaic technology, combining the exceptional optoelectronic properties of perovskite materials with the quantum confinement effects of nanoscale structures. These devices leverage the tunable bandgap and high absorption coefficients of perovskite quantum dots (PQDs) to achieve efficient light harvesting while utilizing mesoporous oxide scaffolds for charge transport. The performance of PQDSCs hinges on several critical factors, including the quality of PQDs, interfacial charge transfer dynamics, and device architecture optimization.

The synthesis of monodisperse PQDs is a foundational step in fabricating high-performance PQDSCs. The hot-injection method is widely employed due to its ability to produce PQDs with narrow size distributions and controlled compositions. In this process, precursors are rapidly injected into a high-temperature solvent, leading to instantaneous nucleation and controlled growth. The reaction parameters, including temperature, precursor concentration, and injection speed, must be precisely tuned to achieve uniformity. Ligand engineering plays a crucial role in stabilizing PQDs and passivating surface defects. Long-chain oleic acid and oleylamine are commonly used ligands, but their insulating nature can hinder charge transfer. Short-chain ligands or hybrid ligand systems have been explored to improve conductivity while maintaining colloidal stability. Post-synthetic ligand exchange processes further enhance the electronic coupling between PQDs and adjacent charge transport layers.

Deposition of PQDs onto mesoporous oxide scaffolds, typically TiO2 or Al2O3, is achieved through techniques such as spin-coating or dip-coating. Spin-coating offers rapid and uniform film formation, with the spinning speed and solution concentration dictating the final thickness. Dip-coating, on the other hand, allows for layer-by-layer assembly, enabling precise control over the loading density of PQDs. Both methods require optimization to ensure complete pore filling while avoiding aggregation or excessive surface coverage that could impede charge transport. The choice of solvent and drying conditions also influences the morphology and adhesion of PQD layers.

Charge transfer dynamics between PQDs and mesoporous oxides are central to the operation of PQDSCs. Upon photoexcitation, electrons are injected from the PQDs into the conduction band of the oxide scaffold, while holes are transported to the counter electrode via a hole-transporting material. The efficiency of electron injection depends on the energy level alignment between the PQDs and the oxide, as well as the quality of the interfacial contact. Transient absorption spectroscopy and time-resolved photoluminescence studies have revealed that electron transfer occurs on picosecond timescales in well-optimized systems. However, competing processes such as charge recombination at the interface or within the PQDs can limit the overall device performance. Surface traps on PQDs, arising from undercoordinated lead atoms or halide vacancies, act as recombination centers and reduce charge collection efficiency.

Strategies to mitigate surface traps include passivation with halide salts, molecular additives, or inorganic shells. For instance, treatment with PbBr2 or CsBr has been shown to fill halide vacancies and improve photoluminescence quantum yields. Encapsulation of PQDs with wide-bandgap materials like SiO2 or Al2O3 can isolate the active cores from environmental degradation while reducing non-radiative recombination. Additionally, the use of gradient heterostructures, where the composition of PQDs is varied to create energy funnels, directs charge carriers away from interfaces and toward collection electrodes.

Recent advancements in PQDSCs have focused on eliminating liquid electrolytes to improve stability and simplify device architecture. Solid-state hole transporters such as spiro-OMeTAD or polymeric materials like P3HT have been integrated to replace traditional iodine-based electrolytes. These junction-free configurations reduce ion migration and corrosion issues, leading to enhanced operational lifetimes. The highest reported power conversion efficiencies for PQDSCs now exceed 16%, achieved through meticulous optimization of PQD synthesis, interfacial engineering, and device fabrication. Key milestones include the development of mixed-cation PQDs (e.g., CsFA or CsMA compositions) that exhibit improved phase stability and broader spectral response.

Stability enhancements have been realized through compositional engineering and encapsulation techniques. All-inorganic PQDs based on CsPbI3 demonstrate superior thermal stability compared to their organic-inorganic counterparts, though their phase stability under ambient conditions remains a challenge. Partial substitution of iodide with bromide or the introduction of small cations like Rb+ has been shown to suppress phase segregation and moisture-induced degradation. Encapsulation with hydrophobic polymers or inorganic barriers further shields PQDs from oxygen and water ingress, extending device lifetimes under continuous illumination or thermal stress.

The future trajectory of PQDSC research involves addressing remaining challenges such as scalability, cost, and environmental impact. Large-area deposition techniques like slot-die coating or spray pyrolysis are being explored to transition from lab-scale to industrial production. The development of lead-free PQDs, utilizing elements like tin or bismuth, aims to mitigate toxicity concerns without compromising optoelectronic performance. Advances in machine learning and high-throughput screening may accelerate the discovery of novel PQD compositions and device architectures.

In summary, PQDSCs leverage the unique properties of perovskite quantum dots to achieve high-efficiency solar energy conversion. The interplay between synthesis, deposition, and interfacial engineering dictates device performance, with ongoing research pushing the boundaries of efficiency and stability. As understanding of charge transfer dynamics and material degradation mechanisms deepens, PQDSCs are poised to become a competitive technology in the photovoltaic landscape.