Efficient and non-hysteresis CH3NH3PbI3/PCBM planar heterojunction solar cells

Highly efficient and non-hysteresis organic/perovskite planar heterojunction solar cells was fabricated by low-temperature, solution-processed method with a structure of ITO/PEDOT:PSS/CH₃NH₃PbI₃/PCBM/Al. The high-quality perovskite thin film was obtained using a solvent-induced-fast-crystallization deposition involving spin-coating the CH₃NH₃PbI₃ solution followed by top-dropping chlorobenzene with an accurate control to induce the crystallization, which results in highly crystalline, pinhole-free, and smooth perovskite thin film. Furthermore, it was found that the molar ratio of CH₃NH₃I to PbI₂ greatly influence the properties of CH₃NH₃PbI₃ film and the device performance. The equimolar or excess PbI₂ was facile to form a flat CH₃NH₃PbI₃ film and produced relatively uniform perovskite crystals. Perovskite solar cells (PSCs) with high-quality CH₃NH₃PbI₃ thin film showed good performance and excellent repeatability. The power conversion efficiency (PCE) up to 13.49% was achieved, which is one of the highest PCEs obtained for low-temperature, solution-processed planar perovskite solar cells based on the structure ITO/PEDOT:PSS/CH₃NH₃PbI₃/PC₆₁BM/Al. More importantly, PSCs fabricated using this method didn’t show obvious hysteresis under different scan direction and speed.     

Improved morphology and enhanced stability via solvent engineering for planar heterojunction perovskite solar cells

Solvent engineering technique for planar heterojunction perovskite solar cells is an efficient way to achieve uniformly controlled grain morphology for perovskite films. In this report, diethyl ether solvent engineering technique was used for Methyl ammonium lead triiodide (CH₃NH₃PbI₃) perovskite thin films for planar heterojunction solar cells which exhibited a PCE of 9.20%. Morphological improvements and enhanced grain sizes leads to enhanced absorption of CH₃NH₃PbI₃. Moreover solar cells have showed an excellent environmental stability of more than 100 days. This increase in efficiency is due to improved film morphology of perovskite layer after solvent treatment which has been revealed under UV–Vis spectroscopy, SEM images, X-ray diffraction and impedance spectroscopy.     

Enhancing the Optoelectronic Performance of Perovskite Solar Cells via a Textured CH3NH3PbI3 Morphology

Perovskite‐based solar cells are generally assembled as planar structures comprising a flat organoammonium metal halide perovskite layer, or mesoscopic structures employing a mesoporous metal‐oxide scaffold into which the perovskite material is infiltrated. To present, little attention has been directed toward the texturing of the perovskite material itself. Herein, a textured CH₃NH₃PbI₃ morphology formed through a thin mesoporous TiO₂ seeding layer and a gas‐assisted crystallization method is reported. The textured morphology comprises a multitiered nanostructure, which allows for significant improvements in the light harvesting and charge extraction performance of the solar cells. Due to these improvements, average short‐circuit current densities for a batch of 28 devices are in excess of 22 mA cm^?2, and the maximum recorded power conversion efficiency is 16.3%. The performance gains concomitant with this textured CH₃NH₃PbI₃ morphology provide further insights into how control of the perovskite microstructure can be used to enhance the cell performance.     

In situ recycle of PbI2 as a step towards sustainable perovskite solar cells

The development of organometal halide perovskite solar cells has grown rapidly and the highest efficiency of the devices has recently surpassed 22%. Because these solar cells contain toxic lead, a sustainable strategy is required to prevent environmental pollution and avoid healthy hazard caused by possible lead outflow. Here, in situ recycling PbI₂ from thermal decomposition CH₃NH₃PbI₃ perovskite films for efficient perovskite solar cells was developed. The thermal behavior of CH₃NH₃PbI₃ perovskite and its individual components were examined by thermogravimetric analysis. By optimizing the process of thermal decomposition CH₃NH₃PbI₃ film, the complete conversion from CH₃NH₃PbI₃ to pure PbI₂ layer with a mesoporous scaffold was achieved. The mesoporous structure readily promotes the conversion efficiency of perovskite and consequently results in high‐performance device. A perovskite crystal growth mechanism on the mesoporous PbI₂ structure was proposed. These results suggest that in situ recycled PbI₂ scaffolds can be a new route in manipulating the morphology of the perovskite active layer, providing new possibilities for high performance. Meanwhile, the risk of lead outflow can be released, and the saving‐energy fabrication of efficient solar cells can be realized.     

Synergistic Effect of PbI2 Passivation and Chlorine Inclusion Yielding High Open‐Circuit Voltage Exceeding 1.15 V in Both Mesoscopic and Inverted Planar CH3NH3PbI3(Cl)‐Based Perovskite Solar Cells

Enhancing open‐circuit voltage in CH₃NH₃PbI₃(Cl) perovskite solar cells has become a major challenge for approaching the theoretical limit of the power conversion efficiency. Here, for the first time, it is demonstrated that the synergistic effect of PbI₂ passivation and chlorine incorporation via controlling the molar ratio of PbI₂, PbCl₂ (or MACl), and MAI in the precursor solutions, boosts the open‐circuit voltage of CH₃NH₃PbI₃(Cl) perovskite solar cells over 1.15 V in both mesoscopic and inverted planar perovskite solar cells. Such high open‐circuit voltage can be attributed to the enhanced photoluminescence emission and carrier lifetime associated with the reduced trap densities. The morphology and composition analysis using scanning electron microscopy, X‐ray diffraction measurements, and energy dispersive X‐ray spectroscopy confirm the high quality of the optimized CH₃NH₃PbI₃(Cl) perovskite film. On this basis, record‐high efficiencies of 16.6% for nonmetal‐electrode all‐solution‐processed perovskite solar cells and 18.4% for inverted planar perovskite solar cells are achieved.     

Enhanced Device Performance of Perovskite Photovoltaics by Magnetic Field‐Aligned Perovskites‐Magnetic Nanoparticles Composite Thin Film

Perovskite photovoltaics have drawn great attention in both academic and industrial sectors in the past decade. To date, impressive device performance has been achieved in state‐of‐the‐art device architectures through morphological manipulation and generic interface engineering. In this study, enhanced device performance of perovskite photovoltaics by magnetic field‐aligned CH₃NH₃PbI₃‐mixed Fe₃O₄ magnetic nanoparticles (CH₃NH₃PbI₃:Fe₃O₄) composite thin films is reported. It is found that magnetic field‐aligned CH₃NH₃PbI₃:Fe₃O₄ composite thin films possess superior film morphology, boosted and balanced charge carrier mobility, and suppressed trap density. Moreover, perovskite photovoltaics by magnetic field‐aligned CH₃NH₃PbI₃:Fe₃O₄ composite thin films exhibit suppressed charge carrier recombination and shorter charge carrier extraction time. As a result, perovskite solar cells by magnetic field‐aligned CH₃NH₃PbI₃:Fe₃O₄ composite thin films exhibit 20.23% power conversion efficiency with significantly reduced photocurrent hysteresis. Moreover, perovskite photodetectors by magnetic field‐aligned CH₃NH₃PbI₃:Fe₃O₄ composite thin films exhibit a photoresponsivity of 858 mA W^?1, a photodetectivity over 10¹³ Jones (1 Jones = 1 cm Hz^1/2 W^?1) and a linear dynamic range over 160 dB at room temperature. All these device performance parameters are significantly better than those by pristine CH₃NH₃PbI₃ thin film. Thus, these studies provide a facile way to boost device performance of perovskite photovoltaics.     

Efficient Perovskite Hybrid Photovoltaics via Alcohol‐Vapor Annealing Treatment

In this work, alcohol‐vapor solvent annealing treatment on CH₃NH₃PbI₃ thin films is reported, aiming to improve the crystal growth and increase the grain size of the CH₃NH₃PbI₃ crystal, thus boosting the performance of perovskite photovoltaics. By selectively controlling the CH₃NH₃I precursor, larger‐grain size, higher crystallinity, and pinhole‐free CH₃NH₃PbI₃ thin films are realized, which result in enhanced charge carrier diffusion length, decreased charge carrier recombination, and suppressed dark currents. As a result, over 43% enhanced efficiency along with high reproducibility and eliminated photocurrent hysteresis behavior are observed from perovskite hybrid solar cells (pero‐HSCs) where the CH₃NH₃PbI₃ thin films are treated by methanol vapor as compared with that of pristine pero‐HSCs where the CH₃NH₃PbI₃ thin films are without any alcohol vapor treatment. In addition, the dramatically restrained dark currents and raised photocurrents give rise to over ten times enhanced detectivities for perovskite hybrid photodetectors, reaching over 10¹³ cm Hz^1/2 W^?1 (Jones) from 375 to 800 nm. These results demonstrate that the method provides a simple and facile way to boost the device performance of perovskite photovoltaics.     

Reduced Defects of MAPbI3 Thin Films Treated by FAI for High‐Performance Planar Perovskite Solar Cells

Organolead trihalide perovskite films with a large grain size and excellent surface morphology are favored to good‐performance solar cells. However, interstitial and antisite defects related trap‐states are originated unavoidably on the surfaces of the perovskite films prepared by the solution deposition procedures. The development of post‐growth treatment of defective films is an attractive method to reduce the defects to form good‐quality perovskite layers. Herein, a post‐treatment tactic is developed to optimize the perovskite crystallization by treating the surface of the one‐step deposited CH₃NH₃PbI₃ (MAPbI₃) using formamidinium iodide (FAI). Charge carrier kinetics investigated via time‐resolved photoluminescent, open‐circuit photovoltage decay, and time‐resolved charge extraction indicate that FAI post‐treatment will boost the perovskite crystalline quality, and further result in the reduction of the defects or trap‐states in the perovskite films. The photovoltaic devices by FAI treatment show much improved performance in comparison to the controlled solar cell. As a result, a champion solar cell with the best power conversion efficiency of 20.25% is obtained due to a noticeable improvement in fill factor. This finding exhibits a simple procedure to passivate the perovskite layer via regulating the crystallization and decreasing defect density.     

Morphological Control for High Performance,Solution‐Processed Planar Heterojunction Perovskite Solar Cells

Organometal trihalide perovskite based solar cells have exhibited the highest efficiencies to‐date when incorporated into mesostructured composites. However, thin solid films of a perovskite absorber should be capable of operating at the highest efficiency in a simple planar heterojunction configuration. Here, it is shown that film morphology is a critical issue in planar heterojunction CH₃NH₃PbI_3‐xCl_x solar cells. The morphology is carefully controlled by varying processing conditions, and it is demonstrated that the highest photocurrents are attainable only with the highest perovskite surface coverages. With optimized solution based film formation, power conversion efficiencies of up to 11.4% are achieved, the first report of efficiencies above 10% in fully thin‐film solution processed perovskite solar cells with no mesoporous layer.     

Improved performance of perovskite solar cells with a TiO2/MoO3 core/shell nanoparticles doped PEDOT:PSS hole-transporter

We demonstrate improved performance of inverted planar heterojunction CH₃NH₃PbI_3-xCl_x perovskite solar cells with a TiO₂/MoO₃ core/shell nanoparticles (NPs) doped poly(3,4-ethylene dioxythiophene):poly(4-styrenesulfonate) (PEDOT:PSS) hole-transporting layer (HTL). TiO₂/MoO₃ Core/shell NPs with size of approximately 40 nm are successfully prepared with a simple wet solution method and are interspersed into PEDOT: PSS layer to construct the HTL. The optimized device shows a high power conversion efficiency of 13.63%, which is dramatically improved compared with the reference device with a pristine PEDOT:PSS HTL. The improvement is mainly attributed to the increased crystalline of the CH₃NH₃PbI_3-xCl_x film with large-scale domains and a compact morphology. More interesting, the cells exhibit superior stability in ambient conditions, which is attributed to the inhibited penetration of moisture due to the compact morphology of the CH₃NH₃PbI_3-xCl_x film and the reduced hygroscopicity of the PEDOT:PSS film.     

Flexible,hole transporting layer-free and stable CH3NH3PbI3/PC61BM planar heterojunction perovskite solar cells

Hole transporting layer (HTL)-free CH₃NH₃PbI₃/PC₆₁BM planar heterojunction perovskite solar cells were fabricated with the configuration of ITO/CH₃NH₃PbI₃/PC₆₁BM/Al. The devices present a remarkable power conversion efficiency (PCE) of 11.7% (12.5% best) under AM 1.5G 100 mW cm⁻² illumination. Moreover, the HTL-free perovskite solar cells on flexible PET substrates are first demonstrated, achieving a power conversion efficiency of 9.7%. The element distribution in the HTL-free perovskite solar cell was further investigated. The results indicated that the PbI₂ enriched near the PC₆₁BM side for chlorobenzene treatment via the fast deposition crystallization method. Without using HTL on the ITO, the device is stable with comparison to that with poly(3,4-ethylenedioxylenethiophene): poly(styrene sulfonate) (PEDOT:PSS) as HTL. In addition, the fabricating time of the whole procedure from ITO substrate cleaning to device finishing fabrication only cost about 3 h for our mentioned devices, which is much more rapid than other structure devices containing other transporting layer. The high efficient and stable HTL-free CH₃NH₃PbI₃/PC₆₁BM planar heterojunction perovskite solar cells with the advantage of saving time and cost provide the potential for commercialization printing electronic devices.     

High-quality CH3NH3PbI3 thin film fabricated via intramolecular exchange for efficient planar heterojunction perovskite solar cells

The high-quality CH₃NH₃PbI₃ perovskite thin film with excellent coverage and uniformity was prepared using an intramolecular exchange technology via a low-temperature, two-step sequential deposition process. The PbI₂(DMSO) complex was synthesized at room temperature without any additives and was deposited, then the CH₃NH₃I solution was deposited subsequently. The further controllable thermal annealing process resulted in the complete formation of flat and uniform CH₃NH₃PbI₃ thin film with large-size grains and (110) preferred crystallographic orientation. The perovskite solar cells (PSCs) with a very simple inverted planar heterojunction structure of ITO/PEDOT:PSS/CH₃NH₃PbI₃/PCBM/Al and without other buffer layers, e.g., C₆₀, LiF, BCP, etc., were fabricated, resulting in a power conversion efficiency (PCE) as high as 14.26%. The results suggest that the low-temperature, two-step sequential deposition process with intramolecular exchange technology provides a good route to fabricate high-quality perovskite thin film and efficient PSCs, which would match with large-scale, high-output roll-to-roll (R2R) printing/coating techniques.     

Thin Films of Dendritic Anatase Titania Nanowires Enable Effective Hole‐Blocking and Efficient Light‐Harvesting for High‐Performance Mesoscopic Perovskite Solar Cells

To achieve high‐performance perovskite solar cells, especially with mesoscopic cell structure, the design of the electron transport layer (ETL) is of paramount importance. Highly branched anatase TiO₂ nanowires (ATNWs) with varied orientation are grown via a facile one‐step hydrothermal process on a transparent conducting oxide substrate. These films show good coverage with optimization obtained by controlling the hydrothermal reaction time. A homogeneous methyl­ammonium lead iodide (CH₃NH₃PbI₃) perovskite thin film is deposited onto these ATNW films forming a bilayer architecture comprising of a CH₃NH₃PbI₃ sensitized ATNW bottom layer and a CH₃NH₃PbI₃ capping layer. The formation, grain size, and uniformity of the perovskite crystals strongly depend on the degree of surface coverage and the thickness of the ATNW film. Solar cells constructed using the optimized ATNW thin films (220 nm in thickness) yield power conversion efficiencies up to 14.2% with a short‐circuit photocurrent density of 20.32 mA cm^?2, an open‐circuit photovoltage of 993 mV, and a fill factor of 0.70. The dendritic ETL and additional perovskite capping layer efficiently capture light and thus exhibit a superior light harvesting efficiency. The ATNW film is an effective hole‐blocking layer and efficient electron transport medium for excellent charge separation and collection within the cells.     

Efficient planar heterojunction perovskite solar cells fabricated by in-situ thermal-annealing doctor blading in ambient condition

The in-situ thermal-annealing doctor blading was developed to fabricate high-quality perovskite CH₃NH₃PbI₃ thin film and efficient planar heterojunction perovskite solar cells (PHJ-PSCs) in ambient condition with humidity of ∼45%. The morphology of CH₃NH₃PbI₃ thin film fabricated by in-situ thermal-annealing doctor blading varied from random nanowires to oriented domains as increasing the substrate temperature, and the domain size became larger and larger with increasing substrate temperature. The PHJ-PSCs with a structure of ITO/PEDOT:PSS/CH₃NH₃PbI₃/PCBM/Ag was fabricated based on in-situ thermal-annealing doctor-bladed CH₃NH₃PbI₃ thin film in ambient condition, resulting in the power conversion efficiency up to 11.29% without obvious hysteresis under different scanning directions and speeds. The performance is comparable to that of PHJ-PSCs fabricated by spin-coating deposition in glovebox with the same structure. The research results suggested that efficient PHJ-PSCs could be fabricated by large-scale in-situ thermal-annealing doctor blading in ambient condition, which is matchable with large-scale, roll-to-roll process and shows potential application in industrial production.     

Controllable Crystallization of CH3NH3Sn0.25Pb0.75I3 Perovskites for Hysteresis‐Free Solar Cells with Efficiency Reaching 15.2%

While Sn? Pb alloyed perovskites have been considered as an effective approach to broaden the absorption spectrum, it is still challenging to modify the crystallization (and thus morphology, crystallinity, and orientation) in a controllable manner and thus boost the efficiency of Sn? Pb alloyed perovskite solar cells. Here, it is unveiled that controlling the crystallization of CH₃NH₃Sn_0.25Pb_0.75I₃ films can be simply realized by adjusting the amount of dimethyl sulfoxide in precursors, which has not been reported in Sn? Pb alloyed perovskite systems. The remarkable perovskite crystallinity enhancement by the 20‐fold enhanced (110) plane intensity in the X‐ray diffraction spectrum of CH₃NH₃Sn_0.25Pb_0.75I₃ and the preferred (110) orientation with the texture coefficient enhanced by 2.6 times to reach 0.88 are demonstrated. Importantly, it is discovered that the introduction of dimethyl sulfoxide avoids the formation of the colloidal coagulation observed in prolonged‐storage precursors and ameliorates inhomogeneous Sn/Pb distributions in resultant perovskite films. Through optimizing perovskite films and device structures, hysteresis‐free planar‐heterojunction CH₃NH₃Sn_0.25Pb_0.75I₃ solar cells with the efficiency reaching 15.2%, which are the most efficient Sn? Pb alloy‐based perovskite solar cells, are achieved.     

Substrate effect on the interfacial electronic structure of thermally-evaporated CH3NH3PbI3 perovskite layer

The impact of substrate work function on the interfacial electronic structure of thermally-evaporated CH₃NH₃PbI₃ perovskite films on various substrates have been systematically investigated using in-situ ultraviolet photoelectron spectroscopy (UPS) and X-ray photoelectron spectroscopy (XPS). On substrates with work function lower than ∼4.43 eV, a Fermi level pinning effect of the lowest unoccupied molecular orbital (LUMO) is observed, resulting in the near zero electron extraction barrier for the CH₃NH₃PbI₃ perovskite solar cells. On the other hand, when substrates with high work function are used, even exceed the highest occupied molecular orbital (HOMO) of CH₃NH₃PbI₃, an almost constant hole extraction barrier of ∼0.88 eV is observed, indicating that the efficiency of hole extraction at these interfaces are low. In order to understand the low hole extraction efficiency at interfaces between CH₃NH₃PbI₃ and these high work function electrodes, the evolution of electronic structures at the interface between CH₃NH₃PbI₃ and MoO₃ is further investigated. The charge transfer and dipole formation between CH₃NH₃PbI₃ and MoO₃ are deduced from the UPS and XPS results, and the energy level alignment between CH₃NH₃PbI₃ and MoO₃ is discussed.     

Vis-Near-Infrared Photodetectors Based on Methyl Ammonium Lead Iodide Thin Films by Pulsed Laser Deposition

Organic–inorganic hybrid perovskite materials are considered as promising candidates for emerging thin-film photodetectors. In this work, we discuss the application of the CH₃NH₃PbI₃ thin films by pulsed laser deposition for photodetection applications. With this method, we obtained good perovskite film coverage on fluorine-doped tin oxide-coated substrates and observed wel- developed grains. The films showed no sign of degradation over several months of testing. We investigated the surface morphology and surface roughness of the films by field emission scanning electron microscopy and atomic force microscopy. The optical response of the films was studied using ultraviolet–visible and photoluminescence spectroscopy. We carried out a study on the solar and infrared photodetection of CH₃NH₃PbI₃ thin films. The values of the responsivity, sensitivity, external quantum efficiency and specific detectivity under 1 sun illumination and 0.7 V bias were 105.4 A/W, 1.9, 2.38 × 10⁴% and 1.5 × 10¹² Jones, respectively.     

利用偏钨酸铵的DMF/水溶液旋涂热解制备WO3薄膜及其在钙钛矿太阳电池致密层中的应用

本文首次通过旋涂热解偏钨酸铵((NH₄)₆H₂W₁₂O₄₀)的DMF/水溶液成功制备了致密的三氧化钨(WO₃)薄膜, 系统研究了WO₃薄膜厚度及用异丙醇冲洗处理气相辅助溶液法制备的CH₃NH₃PbI₃薄膜对相应钙钛矿太阳电池光伏性能的影响. 结果表明, 使用厚度为62nmWO₃致密层的平板钙钛矿太阳电池获得了短路电流密度17.39 mA.cm_-2, 开路电压0.58 V, 填充因子0.57, 相应光电转化效率5.72%. 使用异丙醇冲洗CH₃NH₃PbI₃薄膜后, 相应太阳电池的光电转化效率由5.72 % 升高到7.04 %.     

Efficient lead acetate sourced planar heterojunction perovskite solar cells with enhanced substrate coverage via one-step spin-coating

In planar heterojunction (PHJ) perovskite solar cells (PerSCs) without mesoporous metal oxide skeleton, there is challenge of formation perovskite film with full coverage to the conductive substrate through solution-process the lead halide precursors. Selecting a lead source with more volatile byproducts is an effective approach to obtain much smoother films with smaller and fewer pinholes. Herein, we demonstrate efficient CH₃NH₃PbI₃/PCBM PHJ PerSCs by using lead acetate (Pb(Ac)₂) as lead precursor. The morphology of the perovskite thin films were investigated by scanning electron microscopy (SEM) and atomic force microscopy (AFM), respectively, and the crystalline quality of the perovskite films were investigated by X-ray diffraction (XRD) spectroscopy. Time-resolved photoluminescence (TRPL) was used to investigate the PL lifetime of the perovskite film. The perovskite film derived from Pb(Ac)₂ shows enhanced surface coverage and improved photoluminescence lifetime in comparison with PbI₂ sourced perovskite film. Averaged over 20 individual devices, the power conversion efficiency (PCE) of devices derived from Pb(Ac)₂ reaches 14.81%, much higher than PbI₂ sourced devices by one-step (8.23%) or two-step (10.58%) spin-coating.     

High‐Performance Planar Solar Cells Based On CH3NH3PbI3‐xClx Perovskites with Determined Chlorine Mole Fraction

Solution‐processable hybrid perovskite solar cells are a new member of next generation photovoltaics. In the present work, a low‐temperature two‐step dipping method is proposed for the fabrication of CH₃NH₃PbI_3‐xCl_x perovskite films on the indium tin oxide glass/poly(3,4‐ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS) substrate. The bandgaps of the CH₃NH₃PbI_3‐xCl_x perovskite films are tuned in the range between 1.54 and 1.59 eV by adjusting the PbCl₂ mole fraction (n_Cl/(n_Cl + n_I)) in the initial mixed precursor solution from 0.10 to 0.40. The maximum chlorine mole fraction measured by a unique potentiometric titration method in the produced CH₃NH₃PbI_3‐xCl_x films can be up to 0.220 ± 0.020 (x = 0.660 ± 0.060), which is much higher than that produced by a one‐step spin‐coating method (0.056 ± 0.015, x = 0.17 ± 0.04). The corresponding solar cell with the CH₃NH₃PbI_2.34±0.06Cl_0.66±0.06 perovskite film sandwiched between PEDOT:PSS and C₆₀ layers exhibits a power conversion efficiency as high as 14.5%. Meanwhile, the open‐circuit potential (V_oc) of the device reaches 1.11 V, which is the highest V_oc reported in the perovskite solar cells fabricated on PEDOT:PSS so far.