The phase instability and large energy loss are two obstacles to achieve stable and efficient inorganic‐CsPbI3−xBrx perovskite solar cells. In this work, stable cubic perovskite (α)‐phase CsPbI2Br is successfully achieved by Pb(Ac)2 functioning at the grain boundary under low temperature. Ac− strongly coordinates with CsPbI2Br to stabilize the α‐phase and also make the grain size smaller and film uniform by fast nucleation. PbO is formed in situ at the grain boundary by decomposing Pb(Ac)2 at high‐temperature annealing. The semiconducting PbO effectively passivates the surface states, reduces the interface recombination, and promotes the charge transport in CsPbI2Br perovskite solar cells. A 12% efficiency and good stability are obtained for in situ PbO‐passivated CsPbI2Br solar cells, while Pb(Ac)2‐passivated device exhibits 8.7% performance and the highest stability, much better than the control device with 8.5% performance and inferior stability. This article highlights the extrinsic ionic grain boundary functionalization to achieve stable and efficient inorganic CsPbI3−xBrx materials and the devices.

There exists stronger chemical interaction between Zn2+ and CH3NH3+/I−, which effectively influences the morphology of perovskite film during annealing process.

Both activation energy calculation [12][13][14][15] and experimental results [11,16,17] suggested that I − and MA + are movable ions in perovskite. There are negative concerns on the ionic movement in perovskite solar cells: one is the hysteresis problem which brings difficulty to characterize the device efficiency accurately. The shape of I-V curve is influenced by the voltage scan direction/rate/range, [7,18,19] which correlates with the arrangement of ions under bias. The other concern is that the ion migration which induces phase segregation in perovskite might impair the stability of the devices. [11,20] However, more and more evidences point out the importance of ion movement to achieve high-performance PSCs. Ionic movement leads to self-doping of perovskite materials and ions at the interface effectively setup a built-in field to encourage the charge transport. [6,[20][21][22] The other positive viewpoint is that ions at the interface can modulate the band bending near the interface, forming an Ohm contact to facilitate charge injection. [9,17] Based on the two-sides of the ionic movement, there are tremendous investigations to eliminate the hysteresis of PSCs caused by ions; [14,23] however, very little attention is paid on utilizing the ionic movement to improve the PSC performance, let alone to diminish the hysteresis. [24] Intrinsic ions movement always relates with the MA + and I − vacancies and lattice distortion, while extrinsic ions from the external ions might not induce such trap states, which remains a great challenge to explore.In this work, external Li + /I − is introduced by adding LiI in perovskite. Li is the 3rd element in periodic table, whose size and weight are far less than CH 3 NH 3 + . Therefore, Li + is supposed to be easily movable in perovskite together with I − . The enhanced ionic conductivity and tunable energy band alignment by extrinsic ions are clearly presented. The designed extrinsic ion doping is proved to be benign for both the energy band alignment and crystalline lattice. Results and DiscussionX-ray diffraction (XRD) patterns of the LiI doped samples are indicated in Figure 1a. All peaks are indexed to the conventional MAPbI 3 perovskite diffraction peaks with Miller indices Ionic movement is considered awful in perovskite solar cells (PSCs) for relating with the hysteresis and long-term instability. However, the positive role of ions to enhance the energy band bending for high performance PSC is always overlooked, let alone reducing the hysteresis. In this work, LiI is doped in CH 3 NH 3 PbI 3 . It is observed that the aggregation of Li + /I − tunes the energy level of the perovskite and induces n/p doping in CH 3 NH 3 PbI 3 , which makes charge extraction quite efficient from perovskite to both NiO and [6,6]-phenyl-C61-butyric acid methyl ester (PCBM) layer. Therefore, in NiO/LiI doped perovskite/PCBM solar cells, Li + and I − modulate the interface energy band alignment to facilitate the electron/hole transport and reduce the interface energy loss. On the other hand,...

Herein, we report a flexible high-conductivity transparent electrode (denoted as S-PH1000), based on conducting polymer poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS), and itsapplication to flexible semi-transparentsupercapacitors. A high conductivity of 2673 S/cm was achieved for the S-PH1000 electrode on flexible plastic substrates via a H2SO4 treatment with an optimized concentration of 80 wt.%. This is among the top electrical conductivities of PEDOT:PSS films processed on flexible substrates. As for the electrochemical properties,a high specific capacitance of 161F/g was obtained from the S-PH1000 electrode at a current density of 1 A/g. Excitingly, a specific capacitance of 121 F/g was retained even when the current density increased to 100 A/g, which demonstrates the high-rate property of this electrode. Flexible semi-transparent supercapacitors based on these electrodes demonstrate high transparency, over 60%, at 550 nm. A high power density value, over 19,200 W/kg,and energy density, over 3.40 Wh/kg, was achieved. The semi-transparent flexible supercapacitor was successfully applied topower a light-emitting diode.

Low-cost inorganic copper iodide (CuI) is introduced as a potential oxidizer for hole-transport material (HTM) in perovskite solar cells (PSCs).