Compositional, Processing, and Interfacial Engineering of Nanocrystal- and Quantum-Dot-Based Perovskite Solar Cells

Perovskite solar cells have recently evolved as an ideal candidate for addressing the scalability challenges associated with solar-based renewable energy technologies because of their high photoconversion efficiency and low-cost and low-temperature fabrication methods. While perovskites started out as nanocrystalline light absorbers in mesoporous templates for photovoltaics, currently they are most commonly studied as polycrystalline (thin-film) absorbers or in bilayer architectures combining template-based nanocrystals with a thin-film perovskite overlayer. Of further interest, colloidal perovskite nanocrystals have recently attracted much attention due to their defect tolerance, low voltage losses, bandgap tunability, and potential for large-scale production and fabrication on flexible substrates. While this research area is still in its infancy, it is predicted to offer unique advantages for commercialization based on studies that have tested different compositions, additives, deposition methods, a broad range of device architectures, and a wide variety of selective charge-extraction layers. Several barriers regarding stability, fabrication, interface engineering, carrier mobility, efficiency, and electronic coupling between nanocrystals have yet to be addressed. In this review, we discuss the evolution of perovskite solar cells containing template-based and solution-processed perovskite nanocrystals, highlighting strategies for achieving perovskite compositions with an ideal bandgap and improved thermal, photo-, and structural stability. Furthermore, we outline processing- and interfacial-engineering approaches that utilize perovskite nanocrystals in photovoltaic devices to examine prospects for future research directions and commercialization.