The combination of comprehensive surface passivation and effective interface carriers transfer plays a critical role in high-performance perovskite solar cells. A 2D structure is an important approach for surface passivation of perovskite film, however, its large band gap could compromise carrier transfer. Herein, we synthesize a new molecule 2-thiopheneethylamine thiocyanate (TEASCN) for the construction of bilayer quasi-2D structure precisely on a tin-lead mixed perovskite surface. This bilayer structure can passivate the perovskite surface and ensure effective carriers transfer simultaneously. As a result, the open-circuit voltage (V oc ) of the device is increased without sacrificing shortcircuit current density (J sc ), giving rise to a high certified efficiency from a credible third-party certification of narrow band gap perovskite solar cells. Furthermore, theoretical simulation indicates that the inclusion of TEASCN makes the bilayer structure thermodynamically more stable, which provides a strategy to tailor the number of layers of quasi-2D perovskite structures.Perovskite solar cells are generally regarded as the most promising next-generation thin film solar cells due to their excellent performance and low cost. Driven by composition engineering, [1] crystal growth manipulation, [2] defect passivation, [3] and band alignment, [4] the efficiency of perovskite solar cells has grown rapidly over the past few years. Recently, many reports indicate that interface defects are a critical factor influencing device performance, and tremendous efforts were made to remove surface defects. [3a, 5] The construction of a quasi-2D passivation layer on the surface of the perovskite film is regarded as one of the most promising strategies to remove defects due to its perfectly matched lattice and ease of fabrication. [6]
Regulation of perovskite growth plays a critical role in the development of high-performance optoelectronic devices. However, judicious control of the grain growth for perovskite light emitting diodes is elusive due to its multiple requirements in terms of morphology, composition, and defect. Herein, we demonstrate a supramolecular dynamic coordination strategy to regulate perovskite crystallization. The combined use of crown ether and sodium trifluoroacetate can coordinate with A site and B site cations in ABX3 perovskite, respectively. The formation of supramolecular structure retard perovskite nucleation, while the transformation of supramolecular intermediate structure enables the release of components for slow perovskite growth. This judicious control enables a segmented growth, inducing the growth of insular nanocrystal consist of low-dimensional structure. Light emitting diode based on this perovskite film eventually brings a peak external quantum efficiency up to 23.9%, ranking among the highest efficiency achieved. The homogeneous nano-island structure also enables high-efficiency large area (1 cm2) device up to 21.6%, and a record high value of 13.6% for highly semi-transparent ones.
Halide perovskites are rising as promising luminescent materials for display applications for their sharp emission peaks and high luminescence quantum yield. However, the heavy metal character of lead is one concern that shadows its application. In this work, monolayer Ruddlesden–Popper 2D structural tin perovskite (PEA)2SnI4 (PEA = C8H9NH3+) is explored for a pure red color light emitting diode (LED). The manipulation of crystal growth kinetics enables the formation of highly ordered nanoplates, bringing high luminescence yield approaching 10% with an emission peak at 630 nm. Meanwhile, the highly oriented and ordered nanoplates structure allows effective carrier injection. The LED shows a low turn on voltage of 2.2 V, an external quantum efficiency of 0.52% and a max luminance of 355 cd m−2. The luminescence quantum yield is comparable to the best performing device based on lead perovskites in the pure red emission region. This work provides a strategy to explore 2D structures for efficient macroscale LEDs.
Organometal halide perovskites as the core of the next-generational photovoltaic technologies have attracted remarkable attention due to their advantages of low material cost, easy fabrication, and outstanding photovoltaic properties. [1] Significant efforts have been made to enhance the photovoltaic performance of perovskite solar cells (PSCs). [2] The power conversion efficiency (PCE) has been boosted to about 26%, [3] which is comparable to that of conventional photovoltaic technology based on crystalline silicon. Nevertheless, the device instability suffering from moisture exposure and heat attack is still a significant barrier on the road toward commercialization. [4] It is known that halide perovskites with low formation energy are intrinsically unstable so that they are easy to deteriorate under various external forces. [5] Therefore, how to stabilize the perovskite structure and films is the most important concern in the PSCs.Recently, several effective strategies, including interfacial engineering, additive engineering, dimensional manipulation, and so on, have been applied to improve device stability. [6] Caffeine (1,3,7-trimethylxanthine) was employed as an additive to increase the activation energy of perovskite films through a molecular lock between carboxyl groups and bivalent Pb, yielding PSCs with good thermal stability at 85 C. [7] Lin et al. proved that the introduction of a piperidinium salt into the perovskites could slow down degradation of the perovskite layer under continuous illumination. [8] Additionally, by depositing n-hexyl trimethyl ammonium bromide on the top of the perovskite film, a thin layer of wide-bandgap halide perovskites was formed through an in situ reaction, leading to a high efficiency of 22.7% and good stability both at 85% relative humidity and under one-sun illumination. [9] Despite these progresses, few studies have considered crystallization control of the halide perovskites, which could be a critical approach to concurrently improve both PCE and device stability. Given that the nucleation and crystallization of perovskites during both initial spin-coating and subsequent annealing process are correlated with the PbI 2 precursor solution, [10,11] it is necessary to tune crystallization of perovskite by coordinating the precursor solution to enhance chemical bonding interactions to deliver high-quality and stable perovskite films.
Tin perovskite is rising as the most promising lead-free perovskite for photovoltaic applications. However, the uncontrollable kinetics of crystal growth brings poor crystal quality with a poor orientation and large defect density. In this work, we explored formamidine acetate (FAAc) and ammonium iodide (NH4I) to replace the generally used formamidinium iodide (FAI) in the growth of a tin perovskite film. This triple reagent (FAAc + NH4I + SnI2) method prolongs the reaction path for the growth of the tin perovskite film. It impedes the growth of a three-dimensional (3D) perovskite structure at room temperature while having less impact on the growth of a low-dimensional structure. As a result, the low-dimensional structure formed at room temperature serves as a seed structure for 3D structure growth in subsequent annealing. The tin perovskite film grown using this triple reactant source hence shows enhanced orientation and long carrier lifetimes, leading to an efficiency of 14.6% for tin perovskite solar cells.
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