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Stabilization of the crystal phase of inorganic/organic lead halide perovskites is critical for their high performance optoelectronic devices. However, due to the highly ionic nature of perovskite crystals, even phase stabilized polycrystalline perovskites can undergo undesirable phase transitions when exposed to a destabilizing environment.While various surface passivating agents have been developed to improve the device performance of perovskite solar cells, conventional deposition methods using a protic polar solvent, mainly isopropyl alcohol (IPA), results in a destabilization of the underlying perovskite layer and an undesirable degradation of device properties. We demonstrate the hidden role of IPA in surface treatments and develop a strategy in which the passivating agent is deposited without destabilizing the high quality perovskite underlayer. This strategy maximizes and stabilizes device performance by suppressing the formation of the perovskite d-phase and amorphous phase during surface treatment, which is observed using conventional methods. Our strategy also effectively passivates surface and grain boundary defects, minimizing non-radiative recombination sites, and preventing carrier quenching at the perovskite interface. This results in an opencircuit-voltage loss of only B340 mV, a champion device with a power conversion efficiency of 23.4% from a reverse current-voltage scan, a device with a record certified stabilized PCE of 22.6%, and enhanced operational stability. In addition, our perovskite solar cell exhibits an electroluminescence external quantum efficiency up to 8.9%. Fig. 4 (a) 3D/LP PSC devices with efficiencies measured at MIT and at Newport. (b) Asymptotical measurement on stabilized open-circuit-voltage (V OC,S ). (c) Stabilization of current density. (d) Stabilized J-V curve extracted from (b and c) with stabilized power conversion efficiency (PCE S ) of 22.6%.

Fluorene‐free perovskite light‐emitting diodes (LEDs) with low turn‐on voltages, higher luminance and sharp, color‐pure electroluminescence are obtained by replacing the F8 electron injector with ZnO, which is directly deposited onto the CH3NH3PbBr3 perovskite using spatial atmospheric atomic layer deposition. The electron injection barrier can also be reduced by decreasing the ZnO electron affinity through Mg incorporation, leading to lower turn‐on voltages.

Hybrid blue polymer light emitting diodes (PLEDs) with high efficiencies, luminance >20 000 cd.m -2 and low operating voltages are obtained using processing temperatures ≤150 °C. By briefly applying an electric field across the device prior to measuring (pre-biasing), the PLEDs with unannealed Zn1-xMgxO/Cs2CO3 injectors have maximum luminances three times higher and operating voltages 26% lower than the previous state-of-the-art, which used ZnO cathodes processed at 400 °C. The high performance of our PLEDs is shown to be linked to the filling of trap states in the unannealed oxide cathode. Further reductions in the operating voltage are obtained through reductions in the electron-injection barrier by incorporating Mg into the ZnO cathode, as revealed by electroabsorption spectroscopy. Device characterization also shows that achieving efficient PLEDs requires the use of an interlayer (in our case Cs2CO3) to prevent non-radiative recombination at the cathode. The architecture and device processing methods we develop allow us to produce PLEDs with 80 nm thick emitters that have a turn-on voltage of only 3.7 V. This work takes a major step towards cheap, efficient flexible PLEDs for displays and lighting.PLEDs include inserting an interfacial layer, such as LiF, NaF, CsF, Cs 2 CO 3 or Ba(OH) 2 , between the metal oxide and emitter. 7,8,15 However, the evidence that these interlayers reduce the electroninjection barrier remains inconclusive. 4,7,8,16 Despite this, a double layer of a metal oxide with an interfacial layer is popular in hybrid PLEDs because it combines the robustness of the oxide injectors with the ability to individually control interfacial effects between the injector and emitter. 4,7,8,17,18 These oxides can be combined with air-tolerant interfacial modifiers,

We demonstrate a versatile acoustically active surface consisting of an ensemble of piezoelectric microstructures that are capable of radiating and sensing acoustic waves. A freestanding microstructure array embossed in a single step on a flexible piezoelectric sheet of polyvinylidene fluoride (PVDF) leads to high-quality acoustic performance, which can be tuned by the design of the embossed microstructures. The high sensitivity and large bandwidth for sound generation demonstrated by this acoustically active surface outperform previously reported thin-film loudspeakers using PVDF, PVDF copolymers, or voided charged polymers without microstructures. We further explore the directivity of this device and its use on a curved surface. In addition, high-fidelity sound perception is demonstrated by the surface, enabling its microphonic application for voice recording and speaker recognition. The versatility, high-quality acoustic performance, minimal form factor, and scalability of future production of this acoustically active surface can lead to broad industrial and commercial adoption for this technology.

The environmental stability of hybrid organic–inorganic perovskite (HOIP) materials needs to increase to enable their widespread adoption in thin-film solar and optoelectronic devices. Molecular additives have recently emerged as an effective strategy for regulating HOIP crystal growth and passivating defects. However, to date the choice of additives is largely limited to a dozen or so materials under the design philosophy that high crystallinity is a prerequisite for stable HOIP thin films. In this study, we incorporate porous organic cages (POCs) as functional additives into perovskite thin films for the first time and investigate the HOIP–POC interaction via a combined experimental and computational approach. POCs are significantly larger than the small-molecule additives explored for HOIP synthesis to date but much smaller than polymeric sealants. Partially amorphized composites of MAPbI3 (methylammonium lead iodide, HOIP) and RCC3 (an amine POC) form a network-like surface topography and lead to an increase in the optical bandgap from 1.60 to 1.63 eV. Further in situ optical imaging suggests that RCC3 can delay the MAPbI3 film degradation onset up to 50× under heat and humidity stresses, showing promise for improving reliability in HOIP-based solar-cell and light-emitting applications. Furthermore, there is evidence of molecular interactions between RCC3 and MAPbI3, as fingerprinted by the suppressed N–H stretching mode in MA+ from Fourier transform infrared (FTIR) spectra and density functional theory (DFT) simulations that suggest strong hydrogen bonding between MA+ and RCC3. Given the diversity of POCs and HOIPs, our work opens a new avenue to stabilize HOIPs via tailored molecular interactions with functional organic materials.

The use of molecules as active components to build nanometer-scale devices inspires emerging device concepts that employ the intrinsic functionality of molecules to address longstanding challenges facing nanoelectronics. Using molecules as controllable-length nanosprings, here we report the design and operation of a nanoelectromechanical (NEM) switch which overcomes the typical challenges of high actuation voltages and slow switching speeds for previous NEM technologies. Our NEM switches are hierarchically assembled using a molecular spacer layer sandwiched between atomically smooth electrodes, which defines a nanometer-scale electrode gap and can be electrostatically compressed to repeatedly modulate the tunneling current. The molecular layer and the top electrode structure serve as two degrees of design freedom with which to independently tailor static and dynamic device characteristics, enabling simultaneous low turn-on voltages (sub-3 V) and short switching delays (2 ns). This molecular platform with inherent nanoscale modularity provides a versatile strategy for engineering diverse high-performance and energy-efficient electromechanical devices.

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