Iodide/triiodide redox shuttle-based additives for high-performance perovskite solar cells by simultaneously passivating the cation and anion defects

Complex Metal Oxides as Emerging Inorganic Hole-Transporting Materials for Perovskite Solar Cells

Perovskite solar cells (PSCs) have achieved revolutionary progress during the past decades with a rapidly boosting rate in power conversion efficiencies from 3.8% to 26.1%. However, high-efficiency PSCs with organic hole-transporting materials (HTMs) suffer from inferior long-term stability and high costs. The replacement of organic HTMs with inorganic counterparts such as metal oxides can solve the above-mentioned problems to realize highly robust and cost-effective PSCs. Nevertheless, the widely used simple metal oxide-based HTMs are limited by the low conductivity and poor light transmittance due to the fixed atomic environment. As an emerging family of inorganic HTMs, complex metal oxides with superior structural/compositional flexibility have attracted rapidly increasing interest recently, showing superior carrier conductivity/mobility and superb light transmittance. Herein, the recent advancements in the design and development of complex metal oxide-based HTMs for high-performance PSCs are summarized by emphasizing the superiority of complex metal oxides as HTMs over simple metal oxide-based counterparts. Consequently, several distinct strategies for the design of complex metal oxide-based HTMs are proposed. Last, the future directions and remaining challenges of inorganic complex metal oxide-based HTMs for PSCs are also presented. This review aims to provide valuable guidelines for the further advancements of robust, high-efficiency, and low-cost PSCs.

Organic Semiconductor Based on N, S-Containing Crown Ether Enabling Efficient and Stable Perovskite Solar Cells

The uncoordinated lead cations are ubiquitous in perovskite films and severely affect the efficiency and stability of perovskite solar cells (PSCs). In this work, 15-crown-5 with various heteroatoms are connected to the organic semiconductor carbazole diphenylamine, and two new compounds, CDT-S and CDT-N, are developed to modify the Pb2+ defects in perovskite films through the anti-solvent method. Apart from the oxygen atoms, there are also N atoms on crown ether ring in CDT-N, and both S and N heteroatoms in CDT-S. The heteroatoms enhance the interaction between the crown ether-based semiconductors and the undercoordinated Pb2+ defect in perovskite. Particularly, the stronger interaction between S atoms and Pb2+ further enhances the defect passivation effect of CDT-S than CDT-N, thereby more effectively suppressing the non-radiative recombination of charge carriers. Finally, the efficiency of the device treated with CDT-S is up to 23.05 %. Moreover, the unencapsulated device based on CDT-S maintained 90.5 % of the initial efficiency after being stored under dark conditions for 1000 hours, demonstrating good long-term stability. Our work demonstrates that crown ethers are promising in perovskite solar cells, and the crown ether containing multiple heteroatoms could effectively improve both efficiency and stability of devices.

The role of Pb oxidation state of the precursor in the formation of 2D perovskite microplates

Two-dimensional (2D) lead halide perovskites are an exciting class of materials currently being extensively explored for photovoltaics and other optoelectronic applications. Their ionic nature makes them ideal candidates for solution processing into both thin films and nanostructured crystals. Understanding how 2D lead halide perovskite crystals form is key towards full control over their physical properties, which may enable new physical phenomena and devices. Here, we investigate the effects of the Pb oxidation state of the initial inorganic precursor on the growth of pure-phase (n = 1) - Popper 2D perovskite BA₂PbI₄ in single-step synthesis. We examine the different crystallisation routes in exposing PbO₂ and PbI₂ powders to a BAI : IPA organo-halide solution, by combining in situ optical microscopy, UV-VIS spectroscopy and time-resolved high performance liquid chromatography. So far, works using PbO₂ to synthesise 3D LHPs introduce a preceding step to reduce PbO₂ into either PbO or PbI₂. In this work, we find that BA₂PbI₄ is directly formed when exposing PbO₂ to BAI : IPA without the need for an external reducing agent. We explain this phenomenon by the spontaneous reduction/oxidation of PbO₂/BAI that occurs under iodine-rich conditions. We observe differences in the final morphology (rectangles vs. octagons) and nanocrystal growth rate, which we explain through the different chemistry and iodoplumbate complexes involved in each case. As such, this work spans the horizon of usable lead precursors and offers a new turning knob to control crystal growth in single-step LHP synthesis.