PbI2 Solution Research Articles

A two-layer structured PbI2 thin film for efficient planar perovskite solar cells.

In this paper, a two-layer structured PbI2 thin film was constructed by the spin-coating procedure using a 0.80 M PbI2 solution in DMF and subsequent close-spaced vacuum thermal evaporation using PbI2 powder as a source. The bottom PbI2 thin film was compact with a sheet-like appearance, parallel to the FTO substrate, and can be easily converted to a compact perovskite thin film to suppress the charge recombination of the electrons of the TiO2 conduction band and the holes of the spiro-OMeTAD valence band. The top PbI2 thin film was porous with nano-sheet arrays, perpendicular to the FTO substrate, and can be easily converted to a porous perovskite thin film to improve the hole migration from the perovskite to spiro-OMeTAD and the charge separation at the perovskite/spiro-OMeTAD interface. The planar perovskite solar cells based on the two-layer structured PbI2 thin film exhibited a photoelectric conversion efficiency of 11.64%, along with an open-circuit voltage of 0.90 V, a short-circuit photocurrent density of 19.29 mA cm(-2) and a fill factor of 0.67.

High efficiency stable inverted perovskite solar cells without current hysteresis

The inverted CH3NH3PbI3 cell fabricated using a two-step method with H2O as an additive in a PbI2 solution exhibited an extremely high FF of 85%.

Multifunctional perovskite capping layers in hybrid solar cells

In this study, the crucial role of perovskites capping layers in the TiO2/CH3NH3PbI3 hybrid solar cells is investigated. The capping layers are realized by controlling the concentration of PbI2 solutions in the sequential deposition process. The morphologies of the active layers are studied by high-resolution scanning electron microscopy (HR-SEM). The amount of perovskites in capping layers increases with the concentration of PbI2 solution, and the coverage of perovskite capping layers on TiO2 films is better developed. Except for the correlation between photocurrents and coverages of perovskite proposed by Snaith, we revealed a more detailed relationship between the photovoltaic performances and perovskite capping layers. It is noteworthy that UV-vis absorption increased with perovskites in capping layers. Moreover, according to the diffuse reflection spectra, light scattering, which is beneficial for the conversion efficiency of photons to electrons by directly preventing most of the incident light from transmitting out, is also enhanced due to both the emergence of larger-size particles in the capping layers and the higher effective dielectric coefficient. All of the aforementioned aspects result in high photocurrents up to 20.6 mA cm−2. Efficiency as high as 10.3% is ultimately achieved by a simple control of PbI2 concentration in the sequential deposition process.

Enhancing the Performance of Sensitized Solar Cells with PbS/CH3NH3PbI3 Core/Shell Quantum Dots

We report on the fabrication of PbS/CH3NH3PbI3 (=MAP) core/shell quantum dot (QD)-sensitized inorganic-organic heterojunction solar cells on top of mesoporous (mp) TiO2 electrodes with hole transporting polymers (P3HT and PSS). The PbS/MAP core/shell QDs were in situ-deposited by a modified successive ionic layer adsorption and reaction (SILAR) process using PbI2 and Na2S solutions with repeated spin-coating and subsequent dipping into CH3NH3I (=MAI) solution in the final stage. The resulting device showed much higher efficiency as compared to PbS QD-sensitized solar cells without a MAP shell layer, reaching an overall efficiency of 3.2% under simulated solar illumination (AM1.5, 100 mW·cm(-2)). From the measurement of the impedance spectroscopy and the time-resolved photoluminescence (PL) decay, the significantly enhanced performance is mainly attributed to both reduced charge recombination and better charge extraction by MAP shell layer. In addition, we demonstrate that the MAP shell effectively prevented the photocorrosion of PbS, resulting in highly improved stability in the cell efficiency with time. Therefore, our approach provides method for developing high performance QD-sensitized solar cells.

Synthesis and Characterization of Organic-Inorganic Layered Perovskite Compounds Using Fullerene Derivatives

Layered perovskite (RNH3)2PbI4 (R = organic cation), which contained the fullerene derivatives, [ethyl-3-tert-butoxycarbonylaminopropyl (1,2-methanofullerene C60)]-61,61-di carboxylate iodide (EAF-I) and di [3-tert-butoxycarbonylaminopropyl (1,2-methanofullerene C60)]- 61,61-dicarboxylate diiodide (DAF-I2) in the organic layers were fabricated and compared with previously reported perovkite compound containing N-methyl-2-(4-aminophenyl)-fulleropyrrolidine iodide (AmPF-I). Because the solvent solubilities of EAF-I and DAF-I2 to N,N-dimethylformamide (DMF) were higher than AmPF-I, the film processability of EAF-I and DAF-I2 was improved compared with AmPF-I. The X-ray diffraction patterns proved the construction of the perovskite structure in (EAF)2PbI4 and (AmPF)2PbI4 cast films. EAF was well-organized and closer-packing than AmPF in the perovskite structure. For the diamine-type fullerene, DAF-I2, it is difficult to form layered structure by spin-coated or cast methods. New sharp X-ray diffraction peaks were observed for DAF-I2 films dipped in PbI2 solution. The intercalations and formation of perovskite structure of (DAF)PbI4 were studied.

Chemical and Size Characterization of Layered Lead Iodide Quantum Dots via Optical Spectroscopy and Atomic Force Microscopy

Lead iodide (PbI2) clusters were synthesized from the chemical reaction of NaI (or KI) with Pb(NO3)2 in H2O, D2O, CH3OH, and C3H7OH solvents. The observation of absorption features between the 550 and 350 nm region obtained with an integrating sphere strongly suggests PbI2 quantum dot formation in solution. Comparison of spectra of PbI2 clusters in solution with PbI2 clusters formed by impregnation of PbI2 in four different pore-sized porous silica substrates indicates that the PbI2 cluster size in solution is less than 2.5 nm in the lateral dimension. Atomic force microscopy (AFM) measurements of PbI2 solutions deposited on mica and highly oriented pyrolytic graphite surfaces indicate that the clusters are single layered. The measured height is 1.0 ± 0.1 nm, which is ∼0.3 nm larger than the layer thickness observed for the bulk materials. The swollen layer thickness can be attributed to the intralayer contraction from the strong lateral interaction among PbI2 molecules, which is supported by ab initio calculations. Raman scattering measurements of the LO and TO modes of PbI2 in bulk and in the confined state were also conducted in 50−150 cm-1 region. Three bands observed at 74, 96, and 116 cm-1 for the confined materials are assigned to the TO2, LO2, and LO1 modes, respectively. The relatively small red shift in the LO modes for PbI2 in the porous hosts may be caused by the surface phonon of PbI2 nanoparticles confined in the porous silica.

Pattern formation in precipitation processes. I. The theory of competitive coarsening

The theory of competitive coarsening is formulated and analyzed for applications to the formation of macroscopic precipitation patterns. Previous work is extended to account for ‘‘local coarsening’’ which results if processes on smaller length scales are properly eliminated. Formally the theory includes the width of the local particle size distribution as a dynamical variable and avoids the assumption of monodispersivity. The linear analysis shows that long-wavelength instabilities of the spatially homogeneous system are suppressed in comparison with the results of previous work. Numerical simulations of the nonlinear model are applied to locally perturbed homogeneous systems and produce one precipitation band surrounded by a growing region essentially void of precipitate. Recurrent banding and satellite induction which result under the assumption of monodispersivity are not explained by this theory. The random patterns found experimentally in supercooled PbI2 solutions containing a gel are interpreted as dissolution patterns driven by exceptionally large particles which act as local perturbations. Using an analogy to percolation problems this point of view can rationalize part of the varying appearance of the patterns as well as the sensitivity to the initial salt concentration. The theory also qualitatively describes the ‘‘focusing effect’’ found in recent experiments on Liesegang band formation.