Emerging quantum dot materials are transforming the landscape of solar cell technologies by offering novel optoelectronic properties that surpass conventional quantum dots such as cadmium selenide or lead sulfide. Among these, perovskite quantum dots (PQDs) and two-dimensional (2D) material quantum dots have gained significant attention due to their exceptional tunability, high absorption coefficients, and potential for high-efficiency photovoltaics. These materials present unique advantages but also face synthesis and stability challenges that must be addressed for large-scale deployment.

Perovskite quantum dots, particularly cesium lead halide (CsPbX3, where X = Cl, Br, I) variants, exhibit outstanding photoluminescence quantum yields, often exceeding 90%, and tunable bandgaps across the visible spectrum. Their high defect tolerance allows for efficient charge carrier transport, reducing non-radiative recombination losses common in traditional quantum dots. Additionally, PQDs demonstrate high absorption coefficients, enabling thinner active layers in solar cells while maintaining strong light harvesting. Their solution processability further facilitates low-cost fabrication via spin-coating or inkjet printing, making them attractive for scalable production. Early-stage solar cells incorporating PQDs have achieved power conversion efficiencies exceeding 16%, showcasing their potential despite being in nascent stages of development.

However, perovskite quantum dots face stability issues under environmental stressors such as moisture, oxygen, and prolonged light exposure. The ionic nature of perovskites makes them prone to degradation, necessitating advanced encapsulation techniques or compositional engineering to enhance robustness. For instance, partial substitution of lead with tin or germanium has been explored to improve stability while maintaining optoelectronic performance. Another challenge lies in controlling surface chemistry during synthesis to minimize trap states that impair charge extraction. Hot-injection and ligand-assisted reprecipitation methods have been refined to produce monodisperse PQDs with reduced surface defects, yet reproducibility remains a hurdle for industrial adoption.

Two-dimensional material quantum dots, derived from transition metal dichalcogenides (TMDs) like MoS2 or WS2, offer distinct advantages in solar applications due to their layer-dependent electronic properties and strong excitonic effects. Unlike bulk TMDs, their quantum-confined counterparts exhibit tunable bandgaps and enhanced light-matter interactions, making them suitable for broadband absorption in solar cells. The presence of direct bandgaps in monolayer TMD QDs further enhances their photovoltaic potential. Additionally, their inherent mechanical flexibility and robustness against environmental degradation present a significant advantage over perovskite QDs. Early demonstrations of TMD QD-based solar cells have shown promising external quantum efficiencies, though their power conversion efficiencies currently lag behind perovskite QDs due to challenges in charge transport across inter-dot boundaries.

Synthesis of 2D material quantum dots often involves liquid-phase exfoliation or electrochemical methods, which can introduce variability in size and edge states. Precise control over lateral dimensions and edge termination is critical for optimizing optoelectronic properties, as edge defects can act as recombination centers. Functionalization with organic ligands or heteroatom doping has been employed to mitigate these issues, but achieving uniform dispersion in thin films remains a technical barrier. Furthermore, the scalability of TMD QD production is limited by the yield and cost of precursor materials, necessitating further development in synthetic protocols.

Beyond perovskites and TMDs, emerging quantum dot systems such as carbon dots and graphene quantum dots are being explored for their non-toxicity and unique electronic properties. Carbon-based QDs exhibit tunable photoluminescence and excellent biocompatibility, though their photovoltaic performance is currently limited by lower absorption coefficients and inefficient charge separation. Similarly, antimony chalcogenide QDs have shown promise due to their optimal bandgap for solar energy conversion, but their synthesis requires stringent control over stoichiometry to prevent phase impurities.

Early-stage device architectures incorporating these novel QDs often employ hybrid designs, such as combining PQDs with organic polymers or integrating TMD QDs into heterojunctions with oxide semiconductors. These approaches aim to leverage the strengths of each material while compensating for individual limitations. For instance, perovskite QDs have been embedded in charge-transport matrices to enhance carrier collection, while TMD QDs have been coupled with plasmonic nanoparticles to boost light absorption via localized surface plasmon resonance. Such strategies have led to incremental improvements in device performance, though challenges in interfacial engineering and long-term stability persist.

The environmental impact of emerging quantum dots is another critical consideration. While perovskite QDs offer high efficiency, the presence of lead raises concerns about toxicity and disposal. Research into lead-free alternatives, such as bismuth or double perovskites, is ongoing but has yet to match the performance of lead-based counterparts. Conversely, 2D material QDs and carbon-based QDs present greener alternatives but require further efficiency enhancements to compete with conventional materials.

In summary, emerging quantum dot materials like perovskite and 2D-based QDs hold immense potential for next-generation solar cells due to their superior optoelectronic properties and processing advantages. Perovskite QDs excel in efficiency and tunability but face stability challenges, while 2D material QDs offer robustness and flexibility but require improvements in synthesis and charge transport. Continued advancements in material engineering, surface passivation, and device integration will be essential to unlock their full potential. As research progresses, these novel QDs may pave the way for high-performance, low-cost photovoltaic technologies that complement or surpass existing solar cell platforms.