No abstract

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,