High-quality CH3NH3PbI3 Films Research Articles

Enhanced sensitivity of grain sizes to precursor stoichiometry enables high-quality CH3NH3PbI3 films for efficient perovskite solar cells

We demonstrate that the sensitivity of grain sizes to precursor CH3NH3I/PbI2 molar ratio can be promoted by hydroiodic acid additive for one-step spin-coated CH3NH3PbI3 film. Thus, the full-coverage, high-crystallinity CH3NH3PbI3 film with average grain size of ∼1.75 μm can be obtained by simply adjusting precursor molar ratio. Planar perovskite solar cell (PSC) with this desired film yields the optimized efficiency of 19.29%. Hence, our work suggests a facile precursor stoichiometry engineering through the assistance of hydroiodic acid to obtain efficient CH3NH3PbI3 PSCs.

Enormously improved CH3NH3PbI3 film surface for environmentally stable planar perovskite solar cells with PCE exceeding 19.9%

One of the most important factors governing the photovoltaic efficiency and environmental stability of Perovskite Solar Cells (PSCs) is the quality of their perovskite films. However, the present study demonstrates that CH3NH3PbI3 perovskite films after anti-solvent washing are far from perfect on the surface, where the crystallization degree is quite low with complex multi-phases associated with numerous defects and notable chemical inhomogeneity. Herein, we report a novel anti-solvent washing treatment simply using Hydrogen Iodide (HI) additive in chlorobenzene (CB) which can enormously improve CH3NH3PbI3 films surface with high crystallization phase purity and chemical homogeneity, leading to excellent structural stability under humidity, heat and even tensile force. Based on such high quality films with defect-less surface, fabricated planar PSCs with an architecture of ITO/TiO2/CH3NH3PbI3/Spiro-OMeTAD/MoOx/Au present a champion PCE of 19.94% and improved stability under humidity. Moreover, fabricated flexible planar PSCs on PET/ITO substrates with a champion PCE of 17.32% are shown to be more robust under tensile force than their control devices. The present study thus not only provides more insight into the facile defects passivation process on the surface achieved via balancing halide ions, but also provides a practical but efficient treatment which can be widely used to fabricate high quality CH3NH3PbI3 films for environmentally stable high performance device applications.

High-Quality CH3NH3PbI3 Films Obtained via a Pressure-Assisted Space-Confined Solvent-Engineering Strategy for Ultrasensitive Photodetectors.

High-quality organic-inorganic hybrid perovskite films are crucial for excellent performance of photoelectric devices. Herein, we demonstrate a pressure-assisted space-confined solvent-engineering strategy to grow highly oriented, pinhole-free thin films of CH3NH3PbI3 with large-scale crystalline grains, high smoothness, and crystalline fusion on grain boundaries. These single-crystalline grains vertically span the entire film thickness. Such a film feature dramatically reduces recombination loss and then improves the transport property of charge carriers in the films. Consequently, the photodetector devices, based on the high-quality CH3NH3PbI3 films, exhibit high photocurrent (105 μA under 671 nm laser with a power density of 20.6 mW/cm2 at 10 V), good stability, and, especially, an ultrahigh on/off ratio (Ilight/Idark > 2.2 × 104 under an incident light of 20.6 mW/cm2). These excellent performances indicate that the high-quality films will be potential candidates in other CH3NH3PbI3-based photoelectric devices.

Efficient and stable planar heterojunction perovskite solar cells fabricated under ambient conditions with high humidity

Abstract The quality of perovskite film plays an important role on the performance and stability of perovskite solar cells (PSCs). Herein, dense and uniform perovskite (CH3NH3PbI3) films are fabricated by combining hot-casting technique (HCT) and methylamine (CH3NH2) gas treatment (MGT) under ambient conditions with a relative humidity of about 60%. These high quality CH3NH3PbI3 films are further used to fabricate planar heterojunction (PHJ) PSCs with a structure of ITO/PEDOT:PSS/CH3NH3PbI3/PCBM/Ag, showing a power conversion efficiency (PCE) up to 14.2% with negligible hysteresis. More importantly, these PHJ-PSCs show excellent stability, and over 80% of their original efficiencies could be maintained even stored in air (humidity ∼45%) for 20 days without encapsulation. Meanwhile, the PCE up to 13.6% could be achieved for PHJ-PSCs fully fabricated in air including electron transport layer PCBM. The researches provide an ease-of-fabrication method to fully fabricate highly efficient and stable PHJ-PSCs under ambient conditions with high humidity, which would potentially accelerate the commercialization of PHJ-PSCs.

A Feasible and Effective Post-Treatment Method for High-Quality CH3NH3PbI3 Films and High-Efficiency Perovskite Solar Cells

The morphology control of CH3NH3PbI3 (MAPbI3) thin-film is crucial for the high-efficiency perovskite solar cells, especially for their planar structure devices. Here, a feasible and effective post-treatment method is presented to improve the quality of MAPbI3 films by using methylamine (CH3NH2) vapor. This post-treatment process is studied thoroughly, and the perovskite films with smooth surface, high preferential growth orientation and large crystals are obtained after 10 s treatment in MA atmosphere. It enhances the light absorption, and increases the recombination lifetime. Ultimately, the power conversion efficiency (PCE) of 15.3% for the FTO/TiO2/MAPbI3/spiro-OMeTAD/Ag planar architecture solar cells is achieved in combination with this post-treatment method. It represents a 40% improvement in PCE compared to the best control cell. Moreover, the whole post-treatment process is simple and cheap, which only requires some CH3NH2 solution in absolute ethanol. It is beneficial to control the reaction rate by changing the volume of the solution. Therefore, we are convinced that the post-treatment method is a valid and essential approach for the fabrication of high-efficiency perovskite solar cells.

Third-order nonlinear optical response of CH_3NH_3PbI_3 perovskite in the mid-infrared regime

The third-order nonlinear optical properties of CH3NH3PbI3 perovskite film have been investigated by the Z-scan technique in the mid-infrared (mid-IR) region. We prepared the high-quality CH3NH3PbI3 films with the precursor solutions, and experimentally observed its broadband saturable absorption behavior and large Kerr nonlinearity. The CH3NH3PbI3 perovskite film exhibited a large nonlinear refractive index (~10−12 m2/W) in the mid-IR regime. Our study indicates the great potential of the organic-inorganic perovskite material in the mid-IR nonlinear optics, and might provide some new sights for Kerr nonlinearity based mid-IR nonlinear optical application.

Solvent-Mediated Intragranular-Coarsening of CH3NH3PbI3 Thin Films toward High-Performance Perovskite Photovoltaics.

The deposition of dense and uniform perovskite films with large grains is crucial for fabricating high-performance perovskite solar cells (PSCs). High-quality CH3NH3PbI3 films were produced by a self-induced intragranular-coarsening approach. The perovskite precursor solution contained a Lewis base, N,N-dimethyl sulfoxide (DMSO), and was deposited using a gas-assisted, one-step, spin-coating method that was followed by a solvent vapor-assisted annealing treatment using a mix of DMSO and chlorobenzene (CBZ). Combining solvent-engineering with gas-assisted deposition helps to form intermediate crystalline entities upon evaporation of the parent solvent but retards the otherwise fast reaction between the precursor ingredients. Subsequent cosolvent annealing induces further grain-coarsening via a facilitated dissolution-precipitation process. This technique produced flat CH3NH3PbI3 films featuring large grain microstructures, with well-coarsened subgrains and a reduction of intragranular defects that minimized carrier recombination. The optimized CH3NH3PbI3 films exhibited enhanced crystallinity, excellent carrier transport and injection, as well as suppressed charge recombination. Benefiting from these advantages, PSCs based on the optimized perovskite films delivered a power conversion efficiency of 17.99% and a stabilized power output above 17.30%. This study presents an effective strategy for the fabrication of high-quality, hybrid perovskite films with potential applications in optoelectronic devices.

Facile preparation of high-quality perovskites for efficient solar cells via a fast conversion of wet PbI2precursor films

Facile preparation of high-quality CH3NH3PbI3films with excellent photovoltaic performance by using an annealing-free method and wet PbI2precursor films.

Crystallization process of PbI2 solution in two-step deposition of CH3NH3PbI3 for high-performance perovskite solar cells

High quality CH3NH3PbI3 films have been successfully constructed by two-step method, using the PbI2 solution after dissolution-crystallization-dissolution treatment. Depending on the dense perovskite thin film morphology, a best and repeatable power conversion efficiency of 14.87% was achieved from the CH3NH3PbI3-based solar cells. Furtherly, excellent device stability was also exhibited, which was remained at more than 77% efficiency under 50% humidity for 10 days.

Efficient semi-transparent planar perovskite solar cells using a ‘molecular glue’

Abstract Semitransparent perovskite solar cells are promising for their use in building integrated photovoltaic applications. One critical requirement for this application is the ability to thin down the perovskite absorber layer without sacrificing much of its optimum device efficiency. However, the production of high quality and defect-free very thin films of perovskites in an all low temperature solution processed p-i-n type device structure has been elusive due to the sensitivity of the materials crystallization dynamics and the variability of surface specific interactions. Here, we show that a unique surface passivation method based on thiourea vapor treatment can effectively produce high quality CH3NH3PbI3 thin-films up to 110 nm of thickness on top of a poly(3,4-ethylenedioxythiophene): polystyrene sulfonate (PEDOT:PSS) surface. The thiourea vapor is believed to act as a ‘molecular glue’ by introducing favorable surface interactions in the PEDOT: PSS film with the soft, polarizable inorganic species (i.e. Pb and I) present in the thin-film precursors, and helps to achieve continuous, pinhole-free perovskite films. Using these solution-processed thin and high quality CH3NH3PbI3 films, semitransparent p-i-n planar perovskite-PCBM solar cells are fabricated with an evaporated transparent Ag top electrode, and the solar cells show a high average visible transparency of 34% at a power conversion efficiency level of 8.2%, which are among the highest reported performance values for semitransparent perovskite solar cells. This demonstration provides an excellent example of how surface passivation can be an effective approach to grow high quality all solution-processed semitransparent perovskite films, and will lead to more efficient thin-film optoelectronic devices in the future.

Solution-processed CuOx as an efficient hole-extraction layer for inverted planar heterojunction perovskite solar cells

A solution-processed CuOx film has been successfully integrated as the hole-transporting layer (HTL) for inverted planar heterojunction perovskite solar cells (PVSCs). The CuOx layer is fabricated by simply spin-coating a copper acetylacetonate (Cu(acac)2) chloroform solution onto ITO glass with high transparency in the visible range. The compact and pinhole-free perovskite film with large grain domains is grown on the CuOx film. The inverted PVSCs with the structure of ITO/CuOx/MAPbI3/PC61BM/ZnO/Al are fabricated and show a best PCE of 17.43% under standard AM 1.5G simulated solar irradiation with a VOC of 1.03V, a JSC of 22.42mAcm−2, and a fill factor of 0.76, which is significantly higher and more stable than that fabricated from the often used hole-transporting material PEDOT:PSS (11.98%) under the same experimental conditions. The enhanced performance is attributed to the efficient hole extraction through the CuOx layer as well as the high-quality CH3NH3PbI3 films grown on the CuOx. Our results indicate that low-cost and solution-processed CuOx film is a promising HTL for high performance PVSCs with better stability.

Highly Efficient Planar Perovskite Solar Cells Via Interfacial Modification with Fullerene Derivatives.

Planar heterojunction perovskite solar cells with a high efficiency up to 17.76% are fabricated by modifying the compact TiO2 (c-TiO2) with a [6,6]-phenyl-C61-butyric acid (PCBA) monolayer. High quality CH3NH3PbI3 films can be easily fabricated on PCBA-modified c-TiO2 substrates by a one-step solution processing method. Significant improvements of the device parameters are observed after PCBA modification. A high open-circuit voltage (Voc) of 1.16 V has been achieved, indicating that the PCBA monolayer can act as a hole blocking layer to reduce the trap site density atop the c-TiO2 and the hole recombination at the c-TiO2 /perovskite interface. The enhancement of the fill factor, as well as the partial quenching of the fluorescence of perovskite after modification with PCBA, reveals that the charge extraction is improved.

Dependence of device performance on the thickness of compact TiO2 layer in perovskite/TiO2 planar heterojunction solar cells

Planar heterojunction perovskite solar cells (PHJ-PSCs) based on CH3NH3PbI3/TiO2 with high-quality CH3NH3PbI3 films were fabricated by two-step interdiffusion technology. The photovoltaic performance of PHJ-PSCs, including short-circuit-current (Jsc) and open-circuit-voltage (Voc), was found to be strongly dependent on the thickness of TiO2 layer. The largest Jsc was obtained at an optimized TiO2 thickness of 65 nm, resulting in a moderate power conversion efficiency (PCE) of 8.40% with a device structure of fluorine doped SnO2/compact TiO2/CH3NH3PbI3/Spiro-MeOTAD/Ag. A thicker compact TiO2 film could lead to a lower Voc, and the physical mechanism between the Voc and the thickness of compact TiO2 layer was disclosed.

CuSCN-Based Inverted Planar Perovskite Solar Cell with an Average PCE of 15.6%.

Although inorganic hole-transport materials usually possess high chemical stability, hole mobility, and low cost, the efficiency of most of inorganic hole conductor-based perovskite solar cells is still much lower than that of the traditional organic hole conductor-based cells. Here, we have successfully fabricated high quality CH3NH3PbI3 films on top of a CuSCN layer by utilizing a one-step fast deposition-crystallization method, which have lower surface roughness and smaller interface contact resistance between the perovskite layer and the selective contacts in comparison with the films prepared by a conventional two-step sequential deposition process. The average efficiency of the CuSCN-based inverted planar CH3NH3PbI3 solar cells has been improved to 15.6% with a highest PCE of 16.6%, which is comparable to that of the traditional organic hole conductor-based cells, and may promote wider application of the inexpensive inorganic materials in perovskite solar cells.