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Perovskites have been firmly established as one of the most promising materials for third-generation solar cells. There remain several great and lingering challenges to be addressed regarding device efficiency and stability. The photovoltaic efficiency of perovskite solar cells (PSCs) depends drastically on the charge-carrier dynamics. This complex process includes charge-carrier generation, extraction, transport and collection, each of which needs to be modulated in a favorable manner to achieve high performance. Two-dimensional materials (TDMs) including graphene and its derivatives, transition metal dichalcogenides ( e.g. , MoS 2 , WS 2 ), black phosphorus (BP), metal nanosheets and two-dimensional (2D) perovskite active layers have attracted much attention for application in perovskite solar cells due to their high carrier mobility and tunable work function properties which greatly impact the charge carrier dynamics of PSCs. To date, significant advances have been achieved in the field of TDM-based PSCs. In this review, the recent progress in the development and application of TDMs ( i.e. , graphene, graphdiyne, transition metal dichalcogenides, BP, and others) as electrodes, hole transporting layers, electron transporting layers and buffer layers in PSCs is detailed. 2D perovskites as active absorber materials in PSCs are also summarized. The effect of TDMs and 2D perovskites on the charge carrier dynamics of PSCs is discussed to provide a comprehensive understanding of their optoelectronic processes. The challenges facing the PSC devices are emphasized with corresponding solutions to these problems provided with the overall goal of improving the efficiency and stability of photovoltaic devices. 

The current trend in the miniaturization of electronic devices has driven the investigation into many nanostructured materials. The ferroelectric material barium titanate (BaTiO 3 ) has garnered considerable attention over the past decade owing to its excellent dielectric and ferroelectric properties. This has led to significant progress in synthetic techniques that yield high quality BaTiO 3 nanocrystals (NCs) with well-defined morphologies ( e.g. , nanoparticles, nanorods, nanocubes and nanowires) and controlled crystal phases ( e.g. , cubic, tetragonal and multi-phase). The ability to produce nanoscale BaTiO 3 with controlled properties enables theoretical and experimental studies on the intriguing yet complex dielectric properties of individual BaTiO 3 NCs as well as BaTiO 3 /polymer nanocomposites. Compared with polymer-free individual BaTiO 3 NCs, BaTiO 3 /polymer nanocomposites possess several advantages. The polymeric component enables simple solution processibility, high breakdown strength and light weight for device scalability. The BaTiO 3 component enables a high dielectric constant. In this review, we highlight recent advances in the synthesis of high-quality BaTiO 3 NCs via a variety of chemical approaches including organometallic, solvothermal/hydrothermal, templating, molten salt, and sol–gel methods. We also summarize the dielectric and ferroelectric properties of individual BaTiO 3 NCs and devices based on BaTiO 3 NCs via theoretical modeling and experimental piezoresponse force microscopy (PFM) studies. In addition, viable synthetic strategies for novel BaTiO 3 /polymer nanocomposites and their structure–composition–performance relationship are discussed. Lastly, a perspective on the future direction of nanostructured BaTiO 3 -based materials is presented.