As a promising substitute for toxic lead-based perovskite, tin (Sn)based halide perovskite has drawn much attention for photovoltaic applications.However, unsatisfied open-circuit voltage (V OC ) and fill factor (FF) values of the available Sn-based perovskite solar cells (PSCs) remain a lingering cloud. In this work, we report a bilateral interfacial engineering strategy to fabricate 2D−3D bulk heterojunction Sn-based perovskite solar cells. Specifically, large cation PEAI and bifunctional LiF are evaporated at the bilateral interfaces of a FASnI 3 film. The presence of PEAI improves the V OC and FF of the PSCs via improved surface coverage and the formed 2D−3D bulk heterojunction structure, while the bifunctional LiF (i) lowers the work function of PEDOT:PSS and (ii) facilitates hole extraction at the ITO/PEDOT:PSS interface. This strategy enabled a power conversion efficiency (PCE) of 6.98% with a V OC of 0.47 V and FF of 0.74. Our findings will add critical building bricks toward efficient Snbased PSCs.

All present designs of perovskite light-emitting diodes (PeLEDs) stem from polymer light-emitting diodes (PLEDs) or perovskite solar cells. The optimal structure of PeLEDs can be predicted to differ from PLEDs due to the different fluorescence dynamics and crystallization between perovskite and polymer. Herein, a new design strategy and conception is introduced, "insulator-perovskite-insulator" (IPI) architecture tailored to PeLEDs. As examples of FAPbBr and MAPbBr , it is experimentally shown that the IPI structure effectively induces charge carriers into perovskite crystals, blocks leakage currents via pinholes in the perovskite film, and avoids exciton quenching simultaneously. Consequently, as for FAPbBr , a 30-fold enhancement in the current efficiency of IPI-structured PeLEDs compared to a control device with poly(3,4ethylenedioxythiophene):poly(styrene sulfonate) as hole-injection layer is achieved-from 0.64 to 20.3 cd A -while the external quantum efficiency is increased from 0.174% to 5.53%. As the example of CsPbBr , compared with the control device, both current efficiency and lifetime of IPI-structured PeLEDs are improved from 1.42 and 4 h to 9.86 cd A and 96 h. This IPI architecture represents a novel strategy for the design of light-emitting didoes based on various perovskites with high efficiencies and stabilities.

Tin (Sn)-based perovskites are increasingly attractive because they offer lead-free alternatives in perovskite solar cells. However, depositing high-quality Sn-based perovskite films is still a challenge, particularly for low-temperature planar heterojunction (PHJ) devices. Here, a "multichannel interdiffusion" protocol is demonstrated by annealing stacked layers of aqueous solution deposited formamidinium iodide (FAI)/polymer layer followed with an evaporated SnI layer to create uniform FASnI films. In this protocol, tiny FAI crystals, significantly inhibited by the introduced polymer, can offer multiple interdiffusion pathways for complete reaction with SnI . What is more, water, rather than traditional aprotic organic solvents, is used to dissolve the precursors. The best-performing FASnI PHJ solar cell assembled by this protocol exhibits a power conversion efficiency (PCE) of 3.98%. In addition, a flexible FASnI -based flexible solar cell assembled on a polyethylene naphthalate-indium tin oxide flexible substrate with a PCE of 3.12% is demonstrated. This novel interdiffusion process can help to further boost the performance of lead-free Sn-based perovskites.

2001834 (1 of 8) mobility, and low cost, make this emergent technology very promising. [1-9] Recently, near-infrared and green PeLEDs with external quantum efficiency (EQE) over 20% were reported, [10-13] signifying that we are one step closer to the practical application of PeLEDs in lighting and displays. Several metrics are generally used to assess the performance of PeLEDs. EQE and lifetime are of particular importance among them. Besides, brightness is an intuitive criterion for visible LEDs. [14-16] Most of the previous studies have not yet matched these three metrics simultaneously. For example, the green PeLED with the to-date record-high EQE of 20.3%, the record of PeLEDs so far, had a maximal luminance of 14 000 cd m −2 and 46 h lifetime (measured at continual mode of 100 cd m −2); [11] while for the most stable green PeLED to date (lifetime 250 h measured at initial brightness of 100 cd m −2), the EQE and luminance were 10.5% and 16 436 cd m −2 , respectively. [17] Critical factors that affect the PeLEDs lifetime include the materials stability, the intrinsic defects in perovskites, and most importantly, ion migration within devices. [18-21] Stable perovskites with high luminescence are essential to achieve PeLEDs with both high stability and efficiency. Hybrid organicinorganic perovskites degrade quickly against the heat and environmental moisture. All-inorganic perovskites usually have higher stability, but their PLQY is generally unsatisfactory because of the relatively low film quality. [22] The nonuniform morphology of perovskite films and the high density of defect states are detrimental to the electroluminescence (EL) emission. Intrinsic defects can mediate charge-carrier trapping thus leading to nonradiative recombination loss, which is harmful to the device performance. For efficient PeLEDs with high stability, many efforts have been devoted to reduce the trap states in perovskite films. Introducing large organic ligands is a widely adopted approach, as it can passivate defects and achieve a relatively high film quality by stabilizing the perovskite surfaces or facilitating the formation of low-dimensional perovskites. [13,23-27] Through optimal composition and phase engineering, Yang et al. achieved an EQE of 14.36% and an improved stability for green PeLEDs with quasi-2D perovskites. [27] Meanwhile, Xu et al. demonstrated a highly efficient and stable PeLEDs through the rational design of passivation molecules. [13] The improved stability results from a combination of reduced Joule heating caused by the high efficiency and the suppression of ion migration due to reduced defect density.