Zhuoqiong Zhang

Abstract Doping has been widely used to control the charge carrier concentration in organic semiconductors. However, in conjugated polymers, n-doping is often limited by the tradeoff between doping efficiency and charge carrier mobilities, since dopants often randomly distribute within polymers, leading to significant structural and energetic disorder. Here, we screen a large number of polymer building block combinations and explore the possibility of designing n-type conjugated polymers with good tolerance to dopant-induced disorder. We show that a carefully designed conjugated polymer with a single dominant planar backbone conformation, high torsional barrier at each dihedral angle, and zigzag backbone curvature is highly dopable and can tolerate dopant-induced disorder. With these features, the designed diketopyrrolopyrrole (DPP)-based polymer can be efficiently n-doped and exhibit high n-type electrical conductivities over 120 S cm −1 , much higher than the reference polymers with similar chemical structures. This work provides a polymer design concept for highly dopable and highly conductive polymeric semiconductors.

Interface engineering is imperative to boost the extraction capability in perovskite solar cells (PSCs). We propose a promising approach to enhance the electron mobility and charge transfer ability of tin oxide (SnO2) electron transport layer (ETL) by introducing a two-dimensional carbide (MXene) with strong interface interaction. The MXene-modified SnO2 ETL also offers a preferable growth platform for perovskite films with reduced trap density. Through a spatially resolved imaging technique, profoundly reduced non-radiative recombination and charge transport losses in PSCs based on MXene-modified SnO2 are also observed. As a result, the PSC achieves an enhanced efficiency of 20.65% with ultralow saturated current density and negligible hysteresis. We provide an in-depth mechanistic understanding of MXene interface engineering, offering an alternative approach to obtain efficient PSCs.

Abstract Multiple cation‐composited perovskites are demonstrated as a promising approach to improving the performance and stability of perovskite solar cells (PSCs). However, recipes developed for fabricating high‐performance perovskites in laboratories are always not transferable in large‐scale production, as perovskite crystallization is highly sensitive to processing conditions. Here, using an in situ optical method, the ambient temperature effect on the crystallization process in multiple cation‐composited perovskites is investigated. It is found that the typical solvent‐coordinated intermediate phase in methylammonium lead iodide (MAPbI 3 ) is absent in formamidinium lead iodide (FAPbI 3 ), and nucleation is almost completed in FAPbI 3 right after spin‐coating. Interestingly, it is found that there is noticeable nuclei aggregation in Formamidinium (FA)‐based perovskites even during the spin‐coating process, which is usually only observed during the annealing in MAPbI 3 . Such aggregation is further promoted at a higher ambient temperature or in higher FA content. Instead of the general belief of stress release‐induced crack formation, it is proposed that the origin of the cracks in FA‐based perovskites is due to the aggregation‐induced solute depletion effect. This work reveals the limiting factors for achieving high‐quality FA‐based perovskite films and helps to unlock the existing narrow processing window for future large‐scale production.

Abstract Optimizing the interface between the perovskite and transport layers is an efficient approach to promote the photovoltaic performance of inverted perovskite solar cells (IPSCs). Given decades of advances in bulk materials optimization, the performance of IPSCs has been pushed to its limits by interface engineering with a power conversion efficiency (PCE) over 25% and excellent stability. Herein, an n‐type polymeric semiconducting material, PY‐IT, that has shown remarkable performance in organic photovoltaics, is introduced as an interface regulator between perovskite and ETL. Encouragingly, this polymerized small molecular acceptor (PSMA) exhibits significant effectiveness in both passivation defects and electron transfer facilitation properties with the merits of strong planarity and rotatable linkers, which significantly optimizes perovskite grain growth orientation and added charge transport channels. As a result, the PSMA‐treated IPSC devices obtain an optimal efficiency of 23.57% with a fill factor of 84%, among the highest efficiency among PSMA‐based IPSCs. Meanwhile, the photo‐stability of PSMA devices is eye‐catching, maintaining ≈80% of its initial PCE after 1000 h of simulated 1‐sun illumination under maximal power point tracking. This work combines the achievements of polymer science and IPSC device engineering to provide a new insight into interface regulation of efficient and stable devices.