Large Perovskite Crystals Research Articles

Modification of electron-transport layers with mixed RGO/C60 additive to boost the performance and stability of perovskite solar cells: A comparative study

In perovskite solar cells (PSCs), the transportation of photogenerated electrons can be controlled by the modification of electron-transport layers. In the present study, TiO 2 doped with reduced graphene oxide (RGO) and C 60 was used as an electron-transport layer in hole-transport-free porous perovskite solar cells. The PSCs were fabricated in the laboratory by a single-step method. As the measurements showed, the use of a mixed electron-transport layer in perovskite cells helps to decrease the absorption in perovskite layers in the visible range, while the electron transport is increased. The scanning electron microscopy images and the X-ray diffraction patterns also showed that large perovskite crystals have fewer holes and better morphology than the reference cells fabricated with pure mesoporous TiO 2 . Appropriate amounts of RGO and C 60 were used to compare the parameters of the modified fabricated cells with those of the reference cells. Moreover, the stability of the fabricated cells was examined by the comparison of them to the reference cells. This comparative study showed an increase of efficiency from 5.15% to 9.10% for the untreated and the treated samples respectively. Less cell destruction was also observed over a 32-day period for the treated samples, indicating the improvement of the shelf stability of PSCs through the suggested ETL modification. • TiO 2 doped with reduced graphen oxide (RGO) and C 60 as an electron transport layer in perovskite solar cells. • Decreased Perovskite layer absorption in the visible range by using mixed electron transport layer. • Elimination of Perovskite interface defects by using a mixed electron transport layer.

Large perovskite crystals improve carrier mobility for field-effect transistors

Researchers improve carrier mobility of field-effect transistors by using large perovskite crystals that reduce grain boundaries.

Precursor solution volume-dependent ligand-assisted synthesis of CH3NH3PbBr3 perovskite nanocrystals

Ligand-assisted reprecipitation (LARP) technique is a powerful approach for the synthesis of organometal halide perovskite nanocrystals (PNCs). The morphology and surface property of the formed PNCs which determine their optical properties are ultrasensitive to the synthetic parameters. To guarantee the batch-to-batch reproducibility of PNCs with excellent optical properties, it is of central importance to better understand the factors influencing the formation of PNCs during LARP process. Herein the dual-factor of the amount of perovskite precursor and the polarity of mixture solvent was modified by varying precursor solution volume (PSV) in the LARP system. The concentration, size, surface state and optical properties of the synthesized CH3NH3PbBr3 PNCs as a function of PSV were systematically investigated aiming to understand the influence of the dual-factor on the nucleation and growth of PNCs. Experimental results revealed that few crystal nuclei was generated due to lower amount of precursor at lower PSV, which was favorable for the growth of large perovskite crystals. At the higher PSV, the inhibition of crystal growth with increased amount of precursor was compensated by increasing the polarity of mixture solvent, which led to the dissolution of surface ligands and eventually growth of large perovskite crystals. The obtained results on PSV-dependent synthesis of PNCs will be used as a guide to optimize the synthetic parameters in the LARP process.

Cross-linked Triarylamine-Based Hole-Transporting Layer for Solution-Processed PEDOT:PSS-Free Inverted Perovskite Solar Cells.

The device performance of inverted organic metallohalide perovskite solar cells (OMPSCs) is optimized via tailoring the electrode surfaces with electron- and hole-transporting materials. This work demonstrates the fabrication of PEDOT:PSS-free OMPSCs using a hole-transporting composite material consisting of bilayered vanadium oxide (VO x) and a thermally cross-linked triarylamine-based material X-DVTPD, which contributes to higher Voc and Jsc values. The hydrophobicity of X-DVTPD resulted in the formation of large perovskite crystals and enhanced the stability of OMPSCs. Integration of ionic fullerene derivative, fulleropyrrolidinium iodide, in OMPSCs as a hole-blocking interfacial layer at the interface with Ag proves effective to further boost the device efficiency to 18.08%.

120 mm single-crystalline perovskite and wafers: towards viable applications

As the large single-crystalline silicon wafers have revolutionized many industries including electronics and solar cells, it is envisioned that the availability of large single-crystalline perovskite crystals and wafers will revolutionize its broad applications in photovoltaics, optoelectronics, lasers, photodetectors, light emitting diodes (LEDs), etc. Here we report a method to grow large single-crystalline perovskites including single-halide crystals: CH3NH3PbX3 (X=I, Br, Cl), and dual-halide ones: CH3NH3Pb(Cl x Br1− x )3 and CH3NH3Pb(Br x I1− x )3, with the largest crystal being 120 mm in length. Meanwhile, we have advanced a process to slice the large perovskite crystals into thin wafers. It is found that the wafers exhibit remarkable features: (1) its trap-state density is a million times smaller than that in the microcrystalline perovskite thin films (MPTF); (2) its carrier mobility is 410 times higher than its most popular organic counterpart P3HT; (3) its optical absorption is expanded to as high as 910 nm comparing to 797 nm for the MPTF; (4) while MPTF decomposes at 150 °C, the wafer is stable at high temperature up to 270 °C; (5) when exposed to high humidity (75% RH), MPTF decomposes in 5 h while the wafer shows no change for overnight; (6) its photocurrent response is 250 times higher than its MPTF counterpart. A few electronic devices have been fabricated using the crystalline wafers. Among them, the Hall test gives low carrier concentration with high mobility. The trap-state density is measured much lower than common semiconductors. Moreover, the large SC-wafer is found particularly useful for mass production of integrated circuits. By adjusting the halide composition, both the optical absorption and the light emission can be fine-tuned across the entire visible spectrum from 400 nm to 800 nm. It is envisioned that a range of visible lasers and LEDs may be developed using the dual-halide perovskites. With fewer trap states, high mobility, broader absorption, and humidity resistance, it is expected that solar cells with high stable efficiency maybe attainable using the crystalline wafers.

Construction of high performance CH3NH3PbI3-based solar cells by hot-casting technique

Two-dimensional plane CH3NH3PbI3 crystals in millimeter size have been first successfully constructed on FTO glass coated with mesoporous TiO2 by hot-casting technique. Depending on the closely and continuous arrangement of large perovskite crystals in the film, a best power conversion efficiency (PCE) of 16.01% was achieved along with a photocurrent density of 21.32mA/cm2, an open circuit voltage of 1.07V and a fill factor of 0.70 from the corresponding CH3NH3PbI3-based solar cells with p-i-n structure. Even more exciting was the quite good stability of the hot-casting-based device, which remained at more than 91% under 55% humidity for 10 days.

Fabrication of perovskite films using an electrostatic assisted spray technique: the effect of the electric field on morphology, crystallinity and solar cell performance.

An electric field assisted spray deposition method is employed for improving the perovskite film morphology, crystallinity, and surface coverage, and for further fabricating an efficient solar cell. By applying different voltages ranging from 0.5 to 2.0 kV during spray deposition, we observed a large variation in the film morphology and surface coverage compared to those fabricated without an electric field, which is due to improved atomization from the Coulomb fission process. The optimized applied voltage of 1.5 kV during spraying led to completion of the reaction between CH3NH3I and PbI2 on a hot substrate for pure phase CH3NH3PbI3 thin film formation with improved grain growth and surface coverage. The cells fabricated using perovskite films showed clear applied voltage dependence in the energy conversion process and alleviation in J-V hysteresis; with 1.5 kV applied voltage the average cell efficiency of 8.9% was obtained compared to films fabricated without applying voltage providing only 6.5%. The best efficiencies are 10.9% and 7.37% for applied voltages of 1.5 kV and 0 kV, respectively. The enhancement in efficiency with applied voltage is due to the formation of more uniform and dense films with large perovskite crystals, which resulted in efficient electron transportation (enhanced photocurrent and modified series and shunt resistances) by minimizing the charge carrier recombination at grain boundaries (resulting in enhanced open circuit voltage). With further optimization of the perovskite film thickness by adjusting the CH3NH3I spray volume, the average cell efficiency of ∼11.0% was obtained.

Effects of different chloride precursors on crystal growth of lead halide perovskites

The optimized quantity and nature of a chloride precursor used for the formation of large perovskite crystals with minimal disorder were explored. The effect of the alkyl chain length of an alkyl ammonium chloride precursor on the crystal growth of CH3NH3PbI3 was systematically investigated. It was found that the addition of ethyl ammonium chloride (EACl) increased the crystal size, which is almost twice (88 nm) the size of standard perovskite crystals (47 nm) having a preferential orientation towards the (110) plane. Photoacoustic studies demonstrated that the disorder in the perovskite crystals was highly reduced by the addition of the EACl precursor.

Two-Inch-Sized Perovskite CH3 NH3 PbX3 (X = Cl, Br, I) Crystals: Growth and Characterization.

Two-inch-sized perovskite crystals, CH3 NH3 PbX3 (X=I, Br, Cl), with high crystalline quality are prepared by a solution-grown strategy. The availability of large perovskite crystals is expected to transform its broad applications in photovoltaics, optoelectronics, lasers, photodetectors, LEDs, etc., just as crystalline silicon has done in revolutionizing the modern electronics and photovoltaic industries.