In recent years there has been an outburst of research interest in small biological molecules in the gas phase. [1] By placing these molecules on the ™transparent cover glass∫ of an isolated environment, one can unravel intrinsic properties usually hidden in the complex medium of a real biological system. The need for such gas-phase studies arises from the anticipation that many biological phenomena can be traced to the fundamental properties of the molecular constituents. Both laser spectroscopy and theoretical methods have made great contributions to elucidating the structures and dynamics of nonrigid biomolecules and their solvated complexes in the gas phase. [2] Amino acids are known to exist in various conformations resulting from the flexibility of their structures, which comprise a backbone and a side chain or residue. The conformational variety of amino acids plays a crucial role in determining the three-dimensional structure of proteins and controlling their dynamics. [3] The energy barrier that separates different conformers is typically rather small so that thermal energy at room temperature enables the molecule to freely change from one conformation to another. Therefore, it is not generally feasible to isolate a specific conformer experimentally at room temperature. By employing a supersonic expansion, however, one can cool down the molecule to a temperature low enough to isolate it in various frozen forms, in other words, as individual conformers. Numerous exper-

It is unmistakably paradoxical that the weakest point of the photoactive organic-inorganic hybrid perovskite is its instability against light. Why and how perovskites break down under light irradiation and what happens at the atomistic level of these materials during the degradation process still remains unanswered. In this paper, we revealed the fundamental origin and mechanism for irreversible degradation of hybrid perovskite materials from our new experimental results and ab initio molecular dynamics (AIMD) simulations. We found that the charges generated by light irradiation and trapped along the grain boundaries of the perovskite crystal result in oxygen-induced irreversible degradation in air even in the absence of moisture. The present result, together with our previous experimental finding on the same critical role of trapped charges in the perovskite degradation under moisture, suggests that the trapped charges are the main culprit in both the oxygen-and moisture-induced degradation of perovskite materials. More detailed roles of oxygen and water molecules were investigated by tracking the atomic motions of the oxygen-or water-covered methylammonium lead triiodide (MAPbI3 for CH3NH3PbI3) perovskite crystal surface with trapped charges via AIMD simulation. In the first few picoseconds of our simulation, trapped charges start disrupting the crystal structure, leading to a close-range interaction between oxygen or water molecules and the compositional ions of MAPbI3. We found that there are different degradation pathways depending both on the polarity of the trapped charge and on the kind of gas molecule. Especially, the deprotonation of organic cations was theoretically predicted for the first time in the presence of trapped anionic charges and water molecules. Additionally, we confirmed that a more structurally stable, multi-component perovskite material (with the composition of MA0.6FA0.4PbI2.9Br0.1) exhibited a much longer lifespan than MAPbI3 under light irradiation even in 100% oxygen ambience or humid air.

Perovskite solar cells (PSCs) are of great interest in current photovoltaic research due to their extraordinary power conversion efficiency of ≈20% and boundless potentialities. The high efficiency has been mostly obtained from TiO2‐based PSCs, where TiO2 is utilized as a hole‐blocking, mesoporous layer. However, trapped charges and the light‐induced photocatalytic effect of TiO2 seriously degrade the perovskite and preclude PSCs from being immediately commercialized. Herein, a simplified PSC is successfully fabricated by eliminating the problematic TiO2 layers, using instead a fluorine‐doped tin oxide (FTO)/perovskite/hole–conductor/Au design. Simultaneously, the sluggish charge extraction at the FTO/perovskite interface is overcome by modifying the surface of the FTO to a porous structure using electrochemical etching. This surface engineering enables a substantial increase in the photocurrent density and mitigation of the hysteretic behavior of the pristine FTO‐based PSC; a remarkable 19.22% efficiency with a low level of hysteresis is obtained. This performance is closely approaching that of conventional PSCs and may facilitate their commercialization due to improved convenience, lower cost, greater stability, and potentially more efficient mass production.

Polyaniline doped with camphorsulfonic acid (PANI-CSA) was successfully utilized as a hole transport layer to realize efficient and stable perovskite solar cells.