Huijue Wu

Hole-conductor-free perovskite organic lead iodide heterojunction thin-film solar cells: High efficiency and junction property

Efficient hole-conductor-free organic lead iodide thin film solar cells have been fabricated with a sequential deposition method, and a highest efficiency of 10.49% has been achieved. Meanwhile, the ideal current-voltage model for a single heterojunction solar cell is applied to clarify the junction property of the cell. The model confirms that the TiO2/CH3NH3PbI3/Au cell is a typical heterojunction cell and the intrinsic parameters of the cell are comparable to that of the high-efficiency thin-film solar cells.

Modified Two-Step Deposition Method for High-Efficiency TiO2/CH3NH3PbI3 Heterojunction Solar Cells

Hybrid organic-inorganic perovskites (e.g., CH3NH3PbI3) are promising light absorbers for the third-generation photovoltaics. Herein we demonstrate a modified two-step deposition method to fabricate a uniform CH3NH3PbI3 capping layer with high-coverage and thickness of 300 nm on top of the mesoporous TiO2. The CH3NH3PbI3 layer shows high light-harvesting efficiency and long carrier lifetime over 50 ns. On the basis of the as-prepared film, TiO2/CH3NH3PbI3 heterojunction solar cells achieve a power conversion efficiency of 10.47% with a high open-circuit voltage of 948 mV, the highest recorded to date for hole-transport-material-free (HTM-free) perovskite-based heterojunction cells. The efficiency exceeding 10% shows promising prospects for the HTM-free solar cells based on organic lead halides.

An all-carbon counter electrode for highly efficient hole-conductor-free organo-metal perovskite solar cells

An all-carbon counter electrode has been fabricated for hole-conductor-free organo-metal perovskite heterojunction thin-film solar cells by a simple and low-temperature process. The counter electrode consisted of two parts: a mesoscopic carbon layer for good contact with the perovskite layer, and a piece of industrial flexible graphite sheet as the conducting electrode. Several types of carbon materials were employed in the counter electrodes and tested. From an electrochemical impedance study, it is found that the contact between the counter electrode and perovskite layer has a significant influence on the charge transport properties of the cells. A power conversion efficiency up to 10.2% has been achieved by hole-conductor-free mesoscopic CH3NH3PbI3/TiO2 heterojunction solar cells with the counter electrode containing a composition of graphite and carbon black, which inspires a new promising route towards low-cost and large-scale commercialization of perovskite solar cells.

Efficient hybrid mesoscopic solar cells with morphology-controlled CH3NH3PbI3-xClx derived from two-step spin coating method.

A morphology-controlled CH3NH3PbI3-xClx film is synthesized via two-step solution deposition by spin-coating a mixture solution of CH3NH3Cl and CH3NH3I onto the TiO2/PbI2 film for the first time. It is revealed that the existence of CH3NH3Cl is supposed to result in a preferential growth along the [110] direction of perovskite, which can improve both the crystallinity and surface coverage of perovskite and reduce the pinholes. Furthermore, the formation process of CH3NH3PbI3-xClx perovskite is explored, in which intermediates containing chlorine are suggested to exist. 13.12% of power conversion efficiency has been achieved for the mesoscopic cell, higher than 12.08% of power conversion efficiency of the devices fabricated without CH3NH3Cl via the same process. The improvement mainly lies in the increasing open-circuit photovoltage which is ascribed to the reduction of reverse saturation current density.

Pressure-assisted CH3NH3PbI3 morphology reconstruction to improve the high performance of perovskite solar cells

The pressure is introduced as a parameter in the post-treat process for perovskite solar cells. Via a hot-pressing method, the rough surface of perovskite film becomes smooth, and the pin-holes can be cured. This modified perovskite morphology can help to improve charge transporting and eliminate recombination in the perovskite solar cells. Moreover, significantly enhanced photovoltaic performances with high PCEs of 10.84% and 16.07% are thus achieved in HTM-free type and spiro-OMeTAD based cells, respectively.

Crystal orientation dependence of the dielectric properties for epitaxial BaZr0.15Ti0.85O3 thin films

Epitaxial Ba0.15Zr0.85TiO3 (BZT) ferroelectric thin films with (001), (011), and (111) orientations were, respectively, grown on La0.67Sr0.33MnO3 (LSMO) buffered LaAlO3 substrates by pulsed laser deposition method. The dc electric-field dependence of permittivity and dielectric loss of (001)-, (011)-, and (111)-oriented BZT/LSMO heterostructures obeys the Johnson formula, and the ac electric-field dependence of that obeys the Rayleigh law under the subswitching field region. The anisotropic dielectric properties are attributed to the higher mobility of the charge carriers, the concentration of mobile interfacial domain walls, and boundaries in the (111)-oriental films than in the (110)- and (100)-oriented films.

Control of Charge Transport in the Perovskite CH3NH3PbI3 Thin Film

Carrier density and transport properties in the CH3 NH3 PbI3 thin film have been investigated. It is found that the carrier density, the depletion field, and the charge collection and transport properties in the CH3 NH3 PbI3 absorber film can be controlled effectively by different concentrations of reactants. That is, the carrier properties and the self-doping characteristics in CH3 NH3 PbI3 films are strongly influenced by the reaction thermodynamic and kinetic processes. Furthermore, by employing mixed solvents with ethanol and isopropanol to deposit the CH3 NH3 PbI3 film, the charge collection and transport efficiencies are improved significantly, thereby yielding an overall enhanced cell performance.

Fumed SiO2 modified electrolytes for quantum dot sensitized solar cells with efficiency exceeding 11% and better stability

For quantum dot sensitized solar cells (QDSCs), optimizing interfacial structures by specifically developing new interfacial modification methods to minimize recombination associated with photo-generated carrier transportation and collection is an effective way to achieve highly efficient devices. In this respect, fumed SiO2 nanoparticles have been used as a polysulfide electrolyte additive for improving the interface in a TiO2/QDs/electrolyte for the first time. It was found that the fill factor (FF), open-circuit voltage (Voc) and the cell performance of the devices are significantly enhanced. Additionally, a power conversion efficiency (PCE) of 11.23% is achieved, which is one of the highest efficiencies for liquid-junction QDSCs. Furthermore, the electron transport and recombination processes in the CdSexTe1−x QDSCs with the SiO2 modified electrolyte have been investigated. This revealed that the existence of SiO2 nanoparticles in the electrolyte can create an energy barrier for the recombination between photo-generated electrons from the QDs as well as the recombination between the electrolyte and the injected electrons from TiO2. It is encouraging that CdSexTe1−x QDSCs in SiO2 modified electrolytes can reach a higher electron collection efficiency (98%) and longer electron lifetime. This work provides a simple and convenient method to modify the TiO2/QDs/electrolyte interfaces of QDSCs.

The Effect of Humidity upon the Crystallization Process of Two-Step Spin-Coated Organic–Inorganic Perovskites

Moisture is shown to activate the reaction between PbI2 and methylammonium halides. In addition, two activating mechanisms are proposed for the formation of CH3 NH3 PbI3 and CH3 NH3 PbI3-x Clx films from a series of carefully controlled experiments. When these rapidly formed perovskite films are directly fabricated into the devices, poor photovoltaic properties are found, due to heavy surface charge recombination. However, the cell performance can be significantly enhanced to 13.63 % and to over 12 % in the steady state for CH3 NH3 PbI3 and to 15.50 % and over 14 % in the steady state for CH3 NH3 PbI3-x Clx , if the rapidly formed perovskite film is annealed. Thus, it is believed that moisture (below 60 % RH) is not a problem for the fabrication of highly efficient perovskite solar cells.

Electron-doped superconducting (La,Ce)2CuO4 thin films grown by dc magnetron sputtering and their transport properties

Electron-doped La2?xCexCuO4 (LCCO) thin films were successfully prepared on (100) SrTiO3 substrates by the dc magnetron sputtering method. The optimal-doped films show a highly c-axis oriented single -type structure, and the zero resistance temperature TC0 is 25?K. In the normal state, the nearly quadratic temperature dependence of the resistivity was found and attributed to the Landau?Fermi liquid behaviour due to electron?electron scattering. At the same time, the negative sign of the Hall coefficient for such films well above TC obviously confirms the electron-type nature. The optimal conditions for the growth of single-phase -type LCCO thin films are also discussed in detail.