Organic–inorganic hybrid perovskites are promising candidates for the next-generation solar cells. Many efforts have been made to study their structures in the search for a better mechanistic understanding to guide the materials optimization. Here, we investigate the structure instability of the single-crystalline CH3NH3PbI3 (MAPbI3) film by using transmission electron microscopy. We find that MAPbI3 is very sensitive to the electron beam illumination and rapidly decomposes into the hexagonal PbI2. We propose a decomposition pathway, initiated with the loss of iodine ions, resulting in eventual collapse of perovskite structure and its decomposition into PbI2. These findings impose important question on the interpretation of experimental data based on electron diffraction and highlight the need to circumvent material decomposition in future electron microscopy studies. The structural evolution during decomposition process also sheds light on the structure instability of organic–inorganic hybrid perovskites in solar cell applications.

acknowledge Electron Microscopy Laboratory in Peking University for the use of aberration corrected transmission electron microscope. J.L. and J.Z. conceived and supervised the project; J.Z., G.K. and Y.Z. grew the crystals and did SEM; B.H. carried out AFM and optic microscopy studies with assistances of E.E., J.Y., and S.X.; J.L. carried out crystallographic analysis of 7 ferroic domains; S.C. and P.G. carried out and analyzed HRTEM; Q.L. and H.W. carried out and analyzed synchrotron XRD; A.X., J.Z. and G.K. carried out and analyzed EBSD. J.L. wrote the manuscript, and all authors participated in the revision.

a b s t r a c t ⇑ Corresponding authors.

Ternary I-III-VI quantum dots (QDs) of chalcopyrite semiconductors exhibit excellent optical properties in solar cells. In this study, ternary chalcopyrite CuGaS 2 nanocrystals (2-5 nm) were one-pot anchored on TiO 2 nanoparticles (TiO 2 @CGS) without any long ligand. The solar cell with TiO 2 @CuGaS 2 /N719 has a power conversion efficiency of 7.4%, which is 23% higher than that of monosensitized dye solar cell. Anchoring CuGaS 2 QDs on semiconductor nanoparticles to form QDs/dye co-sensitized solar cells is a promising and feasible approach to enhance light absorption, charge carrier generation as well as to facilitate electron injection comparing to conventional mono-dye sensitized solar cells.

This paper discusses a broadcasting multi-digital signature algorithm based on the elliptic curve cryptosystem. The method overcomes the problem of poor speed digital signature verification due to more complex operations, reduces relatively complex multiplication and point multiplication in the original broadcast multiple digital signature scheme, and avoids matrix inversion. It improves the speed of verification at the same time, and does not affect the security ofthe signature.

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It is essential for flapping-wing micro aerial vehicles to have a driver with compact size, low mass, and high conversion efficiency in low-power application. In this article, a dual-stage low-power converter driving for piezoelectric actuator was designed and implemented, which can be applied in flapping-wing micro aerial vehicles. Using the "simultaneous drive" method, an Residual Current Devices (RCD) passive snubber flyback DC/DC step-up converter cascaded with a bidirectional active half-bridge drive stage is designed. The flyback converter is controlled by pulse width modulation in discontinuous conduction mode to ensure the stability of the output high voltage. The half-bridge drive stage takes the approach of comparing the output voltage signal with an ideal waveform lookup table to generate arbitrary unipolar signals. The proposed converter has a weight of 345 mg, a size of 285 mm 2 (19 Â 15 mm 2 ), a maximum output power of 500 mW, and a maximum conversion efficiency of 64.5%. An experiment driving for piezoelectric actuator was performed to observe the displacement generated by the converter. According to the experimental results, this converter can be applied in flapping-wing micro aerial vehicles.