CH3NH3PbI3 Films Research Articles

High-gain broadband organolead trihalide perovskite photodetector based on a bipolar heterojunction phototransistor

Both a favorable material and designed structure are essential for a high-performance photodetector. For the excellent physical properties of organolead trihalide perovskites, with CH3NH3PbI3 films serving as a base layer, a bipolar heterojunction phototransistor-type perovskite photodetector is proposed. Benefiting from this bipolar heterojunction structure, which is characterized by high gain and low work voltage, an optimized device exhibits high performance with a photoresponsivity of 125 AW−1 and an external efficiency of 3.62 × 104% at 427 nm with a low work voltage of 0.7 V. Additionally, such phototransistors have a broad photoresponsivity from 360 to 820 nm. These results demonstrate that the bipolar heterojunction phototransistor, which is widely used in inorganic materials, is a promising structure for organolead trihalide perovskite optoelectronic devices, paving a new way for developing high-performance photodetectors.

Homeopathic Perovskite Solar Cells: Effect of Humidity during Fabrication on the Performance and Stability of the Device

Rapid degradation in humid environments is a major drawback of methylammonium lead iodide (CH3NH3PbI3), which is the archetypical component of perovskite solar cells. In this work, we have investigated the aging and degradation kinetics of CH3NH3PbI3 films and devices fabricated under controlled conditions as a function of relative humidity (RH) and compared their performance with those that were prepared under dry conditions. The aging and degradation kinetics is monitored by optical absorption and impedance spectroscopy measurements under monochromatic illumination at two different wavelengths. Aged devices show a substantial difference between the recombination rate under red and blue light illumination, which is attributed to the enhancement of local recombination routes upon aging. Interestingly, we observe that this feature is less pronounced in devices prepared under conditions of the highest RH of 50%. In general, we found that these devices keep their original electric properties and withstand a ...

Perovskite Solar Cells Prepared by Advanced Three-Step Method Using Additional HC(NH2)2I Spin-Coating: Efficiency Improvement with Multiple Bandgap Structure

In the conventional two-step prepared perovskite solar cells, the CH3NH3PbI3 (MAPbI3) film usually contains an unreacted PbI2 at the interface between an electron transport layer (ETL) and a perovskite active layer. To reduce the unreacted PbI2 in the two-step prepared MAPbI3 film, we have recently reported a new three-step method, which was realized by an additional MA(I,Br) spin-coating. Here, we propose an advanced three-step method, viz., an additional HC(NH2)2I (FAI) spin-coating on the two-step prepared MAPbI3 film. The additional FAI spin-coating formed a FAxMA1–xPbI3 solid solution by the incorporation of FA ion into MAPbI3. Also, the additional FAI spin-coating yielded a FAyMA1–yPbI3 layer (y > x) by converting the unreacted PbI2, which resulted in the layered structure with different FA concentrations and hence, with the multiple bandgap structure. The best PCE of 18.1% was achieved by optimizing the FAI spin-coating process.

Evidence of Nitrogen Contribution to the Electronic Structure of the CH3 NH3 PbI3 Perovskite.

Despite fast development of hybrid perovskite solar cells, there are many fundamental questions related to the perovskite film which remain open. For example, there are contradicting theoretical reports on the role of the organic methylammonium cation (CH3 NH3+ ) in the methylammonium lead triiodide (CH3 NH3 PbI3 ) perovskite film. From one side it is reported that the organic cation does not contribute to electronic structure of the CH3 NH3 PbI3 film. From the other side, valence band maximum fluctuations, dependent on the CH3 NH3+ rotation, have been theoretically predicted. The resonant X-ray photoelectron spectroscopy results reported here show experimental evidence of nitrogen contribution to the CH3 NH3 PbI3 electronic structure. Moreover, the observed strong resonances of nitrogen with the I 5s and the Pb 5d-6s levels indicate that the CH3 NH3 PbI3 valence band is extended up to ≈18 eV below the Fermi energy, and therefore one should also consider these shallow core levels while modeling its electronic structure.

Enhancement of Morphological and Optoelectronic Properties of Perovskite Films by CH3NH3Cl Treatment for Efficient Solar Minimodules

In order to get homogeneous and high-quality perovskite CH3NH3PbI3 films, different growing methods have been developed, but most of them are unsuitable for scaling up. In this work, we studied in a systematic approach the influence of CH3NH3Cl (MACl) surface treatment in the acetonitrile (ACN) deposition route. This method does not require vacuum nor solvent quenching steps, which make it probably one of the easiest for transference from lab scale to large-area deposition techniques such as roll-to-roll printing. The properties of perovskite films grown by ACN method and the influence of the MACl on the performance of the perovskite solar cells (PSCs) are characterized in detail by different techniques. By atomic force microscopy (AFM) and Kelvin probe force microscopy (KPFM) we found significant differences in the morphology and the work function of the perovskite with and without MACl treatment. Moreover, the microstructure presents very different behavior: after being exposed to radiation, the MACl tr...

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.

One-step roll-to-roll air processed high efficiency perovskite solar cells

The rapid improvement in power conversion efficiencies (PCE) to record high levels have highlighted perovskite solar cells’ great potential to be commercialized in the near future. Continuous roll-to-roll (R2R) processing on flexible substrates enables ultra low-cost and high throughput manufacturing, which is essential for perovskite solar cells to make a breakthrough in cost per Watt compared to commercially established solar cells technologies. Here we demonstrate a facile spin-coating-free and R2R compatible blowing-assisted drop-casting (BADC) method to prepare CH3NH3PbI3 films for perovskite solar cells. The crystallinity and morphology of CH3NH3PbI3 films and device performance are significantly improved by optimization of the formulation with an NH4Cl additive. The perovskite solar cell prepared in air with a maximum PCE of 19.48% is obtained using modified poly(3,4-ethylenedioxythiophene):polystyrene sulfonate (m-PEDOT:PSS) as the hole transport layer (HTL). The cells based on the structure of ITO/m-PEDOT:PSS/CH3NH3PbI3/PCBM/Ca/Al exhibit negligible current hysteresis. The optimized formulation is then successfully applied to slot-die coating on glass and subsequently to R2R on a flexible substrate, giving record PCEs of 15.57% and 11.16%, respectively.

Ultrafast Terahertz Probes of Charge Transfer and Recombination Pathway of CH3NH3PbI3 Perovskites**Supported by the National Natural Science Foundation of China under Grant Nos 11674213, 11604202 and 61735010, the Young Eastern Scholar at Shanghai Institutions of Higher Learning under Grant No QD2015020, the Universities Young Teachers Training Funding Program under Grant No ZZSD15098, and the ‘Chen Guang’ Project of Shanghai Municipal

We use transient terahertz photoconductivity measurements to demonstrate that upon optical excitation of CH3NH3PbI3 perovskite, the hole transfer from CH3NH3PbI3 into the organic hole-transporting material (HTM) Spiro-OMeTAD occurs on a sub-picosecond timescale. Second-order recombination is the dominant decay pathway at higher photo-excitation fluences as observed in neat CH3NH3PbI3 films. In contrast, under similar experimental conditions, second-order recombination weakly contributes the relatively slow recombination between the electrons in the perovskite and the injected holes in HTM, as a loss mechanism at the CH3NH3PbI3/Spiro-OMeTAD interface. Our results offer insights into the intrinsic photophysics of CH3NH3PbI3-based perovskites with direct implications for photovoltaic devices and optoelectronic applications.

BEHAVIORS OF PHOTOCONDUCTIVE DETECTORS BASED ON MAPbI3 PEROVSKITE FILMS

The CH3NH3PbI3 films were synthesized by a facile low-cost solution process and were used to fabricate photoconductive detectors. The perovskite photodetector is very sensitive to light, with a high responsivity of 5.51[Formula: see text]mA/W and a sensitivity of 50 at 5[Formula: see text]V under 350[Formula: see text]nm light illumination. The device exhibits the fast rise and decay processes with similar appearance, and the relaxation time constants are 270 and 300[Formula: see text]ms, respectively. The photo-current shows an evident saturation, without further increase for prolonging the illumination period. The perovskite photodetectors display high responsive performances to short-wavelength lights. This study is expected to provide a fundamental knowledge of perovskite photodetectors with high speed and repeatability for practical applications.

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.

Efficient and Reproducible CH3NH3PbI3 Perovskite Layer Prepared Using a Binary Solvent Containing a Cyclic Urea Additive.

An efficient CH3NH3PbI3 perovskite solar cell whose performance is reproducible and shows reduced dependence on the processing conditions is fabricated using the cyclic urea compound 1,3-dimethyl-2-imidazolidinone (DMI) as an additive to the precursor solution of CH3NH3PbI3. X-ray diffraction analysis reveals that DMI weakly coordinates with PbI2 and forms a CH3NH3PbI3 film (film-DMI) with no intermediate phase. The surface of annealed film-DMI (film-DMI-A) was smooth, with an average crystal size of 1 μm. Photoluminescence and transient photovoltage measurements show that film-DMI-A exhibits a longer carrier lifetime than a CH3NH3PbI3 film prepared using the strongly coordinating additive dimethyl sulfoxide (DMSO) (film-DMSO-A) because of the reduced number of defect sites in film-DMI-A. A solar cell based on film-DMI-A exhibits a higher power conversion efficiency (17.6%) than that of a cell based on film-DMSO-A (15.8%). Furthermore, the performance of the film-DMI-A solar cell is less sensitive to the ratio between PbI2 and DMI, and film-DMI can be fabricated under a high relative humidity of 55%.

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.

Incorporating 4-tert-Butylpyridine in an Antisolvent: A Facile Approach to Obtain Highly Efficient and Stable Perovskite Solar Cells.

The synthesis and growth of CH3NH3PbI3 films with controlled nucleation is a key issue for the high efficiency and stability of solar cells. Here, 4-tert-butylpyridine (tBP) was introduced into a CH3NH3PbI3 antisolvent to obtain high quality perovskite layers. In situ optical microscopy and X-ray diffraction patterns were used to prove that tBP significantly suppressed perovskite nucleation by forming an intermediate phase. In addition, a gradient perovskite structure was obtained by this method, which greatly improved the efficiency and stability of perovskites. An effective power conversion efficiency (PCE) of 17.41% was achieved via the tBP treatment, and the high-efficiency device could maintain over 89% of the initial PCE after 30 days at room temperature.

Ultrafast Imaging of Carrier Cooling in Metal Halide Perovskite Thin Films.

Understanding carrier relaxation in lead halide perovskites at the nanoscale is critical for advancing their device physics. Here, we directly image carrier cooling in polycrystalline CH3NH3PbI3 films with nanometer spatial resolution. We observe that upon photon absorption, highly energetic carriers rapidly thermalize with the lattice at different rates across the film. The initial carrier temperatures vary by many multiples of the lattice temperature across hundreds of nanometers, a factor that cannot be accounted for by excess photon energy above the bandgap alone or in variations of the initial carrier density. Electron microscopy suggests that morphology plays a critical role in determining the initial carrier temperature and that carriers in small crystal domains decay slower than those in large crystal domains. Our results demonstrate that local disorder dominates the observed carrier behavior, highlighting the importance of making local rather than averaged measurements in these materials.

An efficient, flexible perovskite solar module exceeding 8% prepared with an ultrafast PbI2 deposition rate

Large-area, pinhole-free CH3NH3PbI3 perovskite thin films were successfully fabricated on 5 cm × 5 cm flexible indium tin oxide coated polyethylene naphthalate (ITO-PEN) substrates through a sequential evaporation/spin-coating deposition method in this research. The influence of the rate-controlled evaporation of PbI2 films on the quality of the perovskite layer and the final performance of the planar-structured perovskite solar cells were investigated. An ultrafast evaporation rate of 20 Å s−1 was found to be most beneficial for the conversion of PbI2 to CH3NH3PbI3 perovskite. Based on this high-quality CH3NH3PbI3 film, a resultant flexible perovskite solar sub-module (active area of 16 cm2) with a power conversion efficiency of more than 8% and a 1.2 cm2 flexible perovskite solar cell with a power conversion efficiency of 12.7% were obtained.

Performance enhancement of perovskite solar cells using NH4I additive in a solution processing method

A two-step sequential deposition has been widely adopted to fabricate a perovskite film of planar heterojunction organo-lead halide perovskite solar cells. However, in this method complete conversion of Lead iodide (PbI2) into CH3NH3PbI3 is limited by the diffusion of CH3NH3I into PbI2 film, thus limits current density. Here, we report a facile method for enhancing perovskite film morphology by introducing a small amount of ammonium iodide (NH4I) as a halogen additive into PbI2 solution, which can react with PbI2 and forms nanostructured platelet structure that helps to diffusion of CH3NH3I, for further improving CH3NH3PbI3 film morphology. Under the optimized NH4I additive concentration of 5 wt%, the best power conversion efficiency (PCE) is 17.4% achieved, which is an improvement of 14% compared to that of the original device without the additive. SEM studies reveal that addition of NH4I into PbI2 films improves the porosity of the films, which helps to improve the perovskite film morphology by increasing the grain size. The enhancement of CH3NH3PbI3 film morphology is useful for increasing the optical absorption of perovskite film thereby increasing short-circuit current density, whence an improvement in the efficiency of the perovskite solar cell devices. The perovskite solar cells fabricated by this method preserved high crystallinity, negligible hysteresis, reliable reproducibility and improved stability.

CaI2: a more effective passivator of perovskite films than PbI2 for high efficiency and long-term stability of perovskite solar cells

Much less additive content of 0.5% CaI2 instead of 5% PbI2 was incorporated into the CH3NH3PbI3 film and a dense and surface-smooth morphology was obtained with much enlarged crystal grains. The champion PSC based on MAPbI3(CaI2)0.005 layer demonstrated a very high PCE of 19.3% with superior long-term stability.

Influence of Synthesis Conditions on the Morphology and Spectral-Luminescent Properties of Films of Organic-Inorganic Perovskite CH3NH3PbI2.98Cl0.02

The influence of the synthesis conditions (rotation speed used for spin-coating deposition of the film, film drying temperature, and the ratio of the PbI2 and CH3NH3I reactants in solutions) on the microstructure, phase composition, and spectral-luminescent properties of films of organic-inorganic perovskite CH3NH3PbI3–xCl x (x = 0, 0.02) was elucidated.

Graphene assisted effective hole-extraction on In2O3:H/CH3NH3PbI3 interface: Studied by modulated surface spectroscopy

Charge separation in CH3NH3PbI3 (MAPbI3) films deposited on a hydrogen doped indium oxide (In2O3:H) photoelectrode was investigated by modulated surface photovoltage (SPV) spectroscopy in a fixed capacitor arrangement. It was found that In2O3:H reproducibly extracts photogenerated-holes from MAPbI3 films. The oxygen-plasma treatment of the In2O3:H surface is suggested to be a reason for this phenomenon. Introducing graphene interlayer increased charge separation nearly 6 times as compared to that on the In2O3:H/MAPbI3 interface. Furthermore, it is confirmed by SPV spectroscopy that the defects of the MAPbI3 interface are passivated by graphene.

Graphene oxide as an additive to improve perovskite film crystallization and morphology forhigh-efficiency solar cells.

The quality of a perovskite film has a great impact on its light absorption and carrier transport, which is vital to improve high-efficiency perovskite solar cells (PSCs). Herein, it is demonstrated that graphene oxide (GO) can be used as an effective additive in the precursor solution for the preparation of high-quality solution-processed CH3NH3PbI3 (MAIPbI3) films. It is evidenced by scanning electron microscopy that the size of the grains inside these films not only increases but also becomes more uniform after the introduction of an optimized amount of 1 vol% GO. Moreover, 1 vol% GO also enhances the crystallization of perovskite film with intact preferential out-of-plane orientation as proven by 2-dimensional grazing-incidence X-ray diffraction. As a consequence of the improved film quality, enhanced charge extraction efficiency and optical absorption are demonstrated by photoluminescence (PL) spectroscopy and UV-visible absorption spectroscopy, respectively. Using 1 vol% GO, the fabricated champion heterojunction PSC with a structure of ITO/SnO2/perovskite/spiro-OMeTAD/Au shows a significant power conversion efficiency increase to 17.59% with reduced hysteresis from 16.10% for the champion device based on pristine perovskite. The present study thus proposes a simple approach to make use of GO as an effective and cheap addictive for high-performance PSCs with large-scale production capability.