Narrow‐bandgap mixed Pb‐Sn perovskite solar cells (PSCs) have great feasibility for constructing efficient all‐perovskite tandem solar cells, in combination with wide‐bandgap lead halide PSCs. However, the power conversion efficiency of mixed Pb‐Sn PSCs still lags behind lead‐based counterparts. Here, additive engineering using ionic imidazolium tetrafluoroborate (IMBF4) is proposed, where the imidazolium (IM) cation and tetrafluoroborate (BF4) anion efficiently passivate defects at grain boundaries and improve crystallinity, simultaneously relaxing lattice strain, respectively. Defect passivation is achieved by the chemical interaction between the IM cation and the positively charged under‐coordinated Pb2+ or Sn2+ ions, and lattice strain relaxation is realized by lattice expansion with the intercalation of BF4 anions into the perovskite lattice. As a result, the synergistic effects of the cation and anion in the IMBF4 additive greatly enhance the optoelectronic performance of half‐mixed Pb‐Sn perovskites, leading to much longer carrier lifetimes. The best‐performing half‐mixed Pb‐Sn PSC shows an efficiency above 19% with negligible hysteresis, while retaining over 90% of its initial efficiency after 1000 h in a nitrogen‐filled glovebox and showing a lifetime to 80% degradation of 53.5 h under continuous illumination.
Layered Ruddlesden–Popper perovskite (RPP) photovoltaics have gained substantial attention owing to their excellent air stability. However, their photovoltaic performance is still limited by the unclear real-time charge-carrier mechanism of operating...
Far-field optical nanoscopy has been widely used to image small objects with sub-diffraction-limit spatial resolution. Particularly, reversible saturable optical fluorescence transition (RESOLFT) nanoscopy with photoswitchable fluorescent proteins is a powerful method for super-resolution imaging of living cells with low light intensity. Here we demonstrate for the first time the implementation of RESOLFT nanoscopy for a biological system using organic fluorophores, which are smaller in size and easier to be chemically modified. With a covalently-linked dye pair of Cy3 and Alexa647 to label subcellular structures in fixed cells and by optimizing the imaging buffer and optical parameters, our RESOLFT nanoscopy achieved a spatial resolution of ~74 nm in the focal plane. This method provides a powerful alternative for low light intensity RESOLFT nanoscopy, which enables biological imaging with small organic probes at nanoscale resolution.
Rendering a high crystalline perovskite film is integral to achieve superior performance of perovskite solar cells (PSCs). Here, we established a two-dimensional liquid cage annealing system, a unique methodology for remarkable enhancement in perovskite crystallinity. During thermal annealing for crystallization, wet-perovskite films were suffocated by perfluorodecalin with distinctively low polarity, nontoxic, and chemically inert characteristics. This annealing strategy facilitated enlargement of perovskite grain and diminution in the number of trap states. The simulation results, annealing time, and temperature experiments supported that the prolonged diffusion length of precursor ions attributed to the increase of perovskite grains. Consequently, without any complicated handling, the performance of perovskite photovoltaics was remarkably improved, and the monolithic grains which directly connected the lower and upper electrode attenuated hysteresis.
The development of high‐performance hole transport layer (HTL)‐free perovskite solar cells (PSCs) with a simplified device structure has been a major goal in the commercialization of PSCs due to the economic advantage of low manufacturing cost. Unfortunately, low bandgap (Eg) mixed Pb–Sn perovskites, which have promising utility for constructing efficient all‐perovskite tandem solar cells, have rarely been explored in simplified HTL‐free device configurations. In this study, efficient band bending and defect engineering at the interface between perovskite and indium tin oxide (ITO) are realized via a binary additive system using copper thiocyanate (CuSCN) and glycine hydrochloride (GlyHCl). Using mixed Pb–Sn perovskites decorated with crystalline p‐type CuSCN, the energy level alignment at the hole extractive interface is modulated in favor of hole extraction, simultaneously increasing hole mobility. Suppressed nonradiative carrier recombination in the perovskite bulk, or across the charge extractive interface, is further achieved by GlyHCl without disturbing the efficient hole transfer characteristics. Notably, a more optimized band alignment is achieved at the hole extractive interface with the addition of GlyHCl. The HTL‐free mixed Pb–Sn PSC shows an efficiency up to 20.1% under forward bias with negligible hysteresis, comparable to state‐of‐the‐art high‐performance full‐structured mixed Pb–Sn PSCs.
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