Nucleation and Crystal Growth of Organic–Inorganic Lead Halide Perovskites under Different Relative Humidity

Organic–inorganic lead halide perovskite compounds are very promising materials for high-efficiency perovskite solar cells. But how to fabricate high-quality perovksite films under controlled humidity conditions is still an important issue due to their sensitivity to moisture. In this study, we investigated the influence of ambient humidity on crystallization and surface morphology of one-step spin-coated perovskite films, as well as the performance of solar cells based on these perovskite films. On the basis of experimental analyses and thin film growth theory, we conclude that the influence of ambient humidity on nucleation at spin-coating stage is quite different from that on crystal growth at annealing stage. At the spin-coating stage, high nucleation density induced by high supersaturation prefers to appear under anhydrous circumstances, resulting in layer growth and high coverage of perovskite films. But at the annealing stage, the modest supersaturation benefits formation of perovskite films with good crystallinity. The films spin-coated under low relative humidity (RH) followed by annealing under high RH show an increase of crystallinity and improved performance of devices. Therefore, a mechanism of fast nucleation followed by modest crystal growth (high supersaturation at spin-coating stage and modest supersaturation at annealing stage) is suggested in the formation of high-quality perovskite films

Enhanced Performance of Photoelectrochemical Water Splitting with ITO@α-Fe₂O₃ Core–Shell Nanowire Array as Photoanode

Hematite (α-Fe₂O₃) is one of the most promising candidates for photoelectrodes in photoelectrochemical water splitting system. However, the low visible light absorption coefficient and short hole diffusion length of pure α-Fe₂O₃ limits the performance of α-Fe₂O₃ photoelectrodes in water splitting. Herein, to overcome these drawbacks, single-crystalline tin-doped indium oxide (ITO) nanowire core and α-Fe₂O₃ nanocrystal shell (ITO@α-Fe₂O₃) electrodes were fabricated by covering the chemical vapor deposited ITO nanowire array with compact thin α-Fe₂O₃ nanocrystal film using chemical bath deposition (CBD) method. The <i>J</i>–<i>V</i> curves and IPCE of ITO@α-Fe₂O₃ core–shell nanowire array electrode showed nearly twice as high performance as those of the α-Fe₂O₃ on planar Pt-coated silicon wafers (Pt/Si) and on planar ITO substrates, which was considered to be attributed to more efficient hole collection and more loading of α-Fe₂O₃ nanocrystals in the core–shell structure than planar structure. Electrochemical impedance spectra (EIS) characterization demonstrated a low interface resistance between α-Fe₂O₃ and ITO nanowire arrays, which benefits from the well contact between the core and shell. The stability test indicated that the prepared ITO@α-Fe₂O₃ core–shell nanowire array electrode was stable under AM1.5 illumination during the test period of 40 000 s

<i>In Situ</i> Fabrication of Highly Conductive Metal Nanowire Networks with High Transmittance from Deep-Ultraviolet to Near-Infrared

We have developed a facile and compatible method to <i>in situ</i> fabricate uniform metal nanowire networks on substrates. The as-fabricated metal nanowire networks show low sheet resistance and high transmittance (2.2 Ω sq^–1 at <i>T</i> = 91.1%), which is equivalent to that of the state-of-the-art metal nanowire networks. We demonstrated that the transmittance of the metal networks becomes homogeneous from deep-ultraviolet (200 nm) to near-infrared (2000 nm) when the size of the wire spacing increases to micrometer size. Theoretical and experimental analyses indicated that we can improve the conductivity of the metal networks as well as keep their transmittance by increasing the thickness of the metal films. We also carried out durability tests to demonstrate our as-fabricated metal networks having good flexibility and strong adhesion