Influence of the surface treatment of PEDOT:PSS layer with high boiling point solvent on the performance of inverted planar perovskite solar cells

Since perovskite precursor solution is typically prepared from high boiling point solvents, understanding the effect of high boiling point solvent treatment of the PEDOT:PSS layer on the performance of perovskite solar cells is important for device processing optimization. In this paper, influence of the surface treatment of the PEDOT:PSS layer with high boiling point solvent, including N,N-dimethylformamide (DMF), dimethyl sulfoxide (DMSO), and ethylene glycol (EG), on the device performance of the perovskite solar cells was investigated. Increased conductivity was measured for the PEDOT:PSS film after solvent treatments, which was ascribed to the partial removal of PSS component from the PEDOT:PSS layer, as evidenced by the UV–vis absorption spectroscopy and XPS spectroscopy. In comparison with the reference cell, poorer device performance was obtained for the perovskite solar cells directly deposited on the solvent washed PEDOT:PSS film, which was ascribed to the increased pin hole density of the perovskite films. However, insertion of a thin PSSNa layer between the PEDOT:PSS layer and the perovskite layer greatly improved device performance, demonstrating that PSS-rich surface is favorite for the crystal growth of the perovskite film. Increased external quantum efficiency over 600–750 nm was measured for the cells based on solvent treated PEDOT:PSS layer, leading to a short circuit current and the consequent performance enhancement.     

Self-Powered Red/UV Narrowband Photodetector by Unbalanced Charge Carrier Transport Strategy

Narrowband photodetector (NB-PD) with selective light detection is critical for artificial vision and imaging. Intrinsic (optical-filter-free) NB-PDs using conjugated organics or halide perovskite materials have been developed for eliminating the current complex filtering systems in NB-PDs. However, the poor performance and external driving circuit of organic NB-PDs as well as complex doping and uncontrollable recombination reactions in typical perovskite NB-PDs have limited their applicational diversification. A p-type self-doped perovskite for intrinsic NB detection is reported which exhibits unique unbalanced electron–hole transfer kinetics. In conjunction with the optical field distribution, an unbalanced charge transport within the self-doped perovskite triggers a wavelength-dependent photo-carrier collection, resulting in a novel spontaneous internal quantum efficiency narrowing mechanism. As a result, by reverting the device architectural polarity, an NB detection at a monochromic light of either red or UV is observed. Using such a revertible asymmetric device design, self-powered NB-PDs are successfully achieved. Briefly, the corresponding NB-PDs exhibit excellent narrow response with a response window of ≈100 nm, high detectivity ≈10¹¹ Jones, and fast response speed (f_−3dB ≈ 60 kHz) at zero bias. These results demonstrate a new strategy of manipulating internal charge transport to realize power-free and filter-free intrinsic NB-PDs.     

Voltage‐Dependent Multicolor Electroluminescent Device Based on Halide Perovskite and Chalcogenide Quantum‐Dots Emitters

Electroluminescent devices based on metal halide perovskites have attracted extensive attention owing to their high external quantum efficiency, excellent color purity, and inexpensive solution process. So far, extensive efforts have been made to improve the efficiency of the monochromatic perovskite light‐emitting diodes (LEDs). However, multicolor perovskite‐based LEDs are seldom studied. Here, an individual device capable of multicolor emission in response to the passage of external electric bias is demonstrated. With the rational design of the energy band alignment and control of the carrier transport property, color‐tunable electroluminescent devices based on inorganic halide perovskite and chalcogenide quantum‐dots are fabricated with a wide color tuning range, high color reversibility, and ultrafast color switching. The mechanism of chromaticity tuning is investigated and is explained by the shift of the exciton recombination zone with the driving voltage. The presented work will impact scientific communities by encouraging the manufacture of cost‐effective, high‐resolution, and full‐color displays and human‐centric lighting.     

Semitransparent,Flexible, and Self‐Powered Photodetectors Based on Ferroelectricity‐Assisted Perovskite Nanowire Arrays

Transparent and flexible photodetectors hold great promise in next‐generation portable and wearable optoelectronic devices. However, most of the previously reported devices need an external energy power source to drive its operation or require complex fabrication processes. Herein, designed is a semitransparent, flexible, and self‐powered photodetector based on the integrated ferroelectric poly(vinylidene‐fluoride‐trifluoroethylene) (P(VDF‐TrFE)) and perovskite nanowire arrays on the flexible polyethylene naphthalate substrate via a facile imprinting method. Through optimizing the treatment conditions, including polarization voltage, polarization time, and the concentration of P(VDF‐TrFE), the resulting device exhibits remarkable detectivity (7.3 × 10¹² Jones), fast response time (88/154 µs) at zero bias, as well as outstanding mechanical stability. The excellent performance is attributed to the efficient charge separation and transport originating from the highly oriented 1D transport pathway and the polarization‐induced internal electric field within P(VDF‐TrFE)/perovskite hybrid nanowire arrays.     

Quasi‐2D Inorganic CsPbBr3 Perovskite for Efficient and Stable Light‐Emitting Diodes

Metal halide perovskites are rising as a competitive material for next‐generation light‐emitting diodes (LEDs). However, the development of perovskite LEDs is impeded by their fast carriers diffusion and poor stability in bias condition. Herein, quasi‐2D CsPbBr₃ quantum wells homogeneously surrounded by inorganic crystalline Cs₄PbBr₆ of large bandgap are grown. The centralization of carriers in nanoregion facilitates radiative recombination and brings much enhanced luminescence quantum yield. The external quantum efficiency and luminescence intensity of the LEDs based on this nanocomposite are one order of magnitude higher than the conventional low‐dimensional perovskite. Meanwhile, the use of inorganic nanocomposite materials brings much improved device operation lifetime under constant electrical field.     

Synergistic Effect of Dual Ligands on Stable Blue Quasi‐2D Perovskite Light‐Emitting Diodes

Since the emergence of inorganic–organic hybrid perovskites a few years ago, there have been many promising achievements in the field of green and red perovskite light‐emitting diodes (PeLEDs). Nevertheless, the performance of blue‐light PeLEDs faces challenges. In this work, the unique synergy obtained by introducing two different ligands to successfully form quasi‐2D perovskite films, which can exhibit stable blue‐light emission, is utilized. The fabricated PeLEDs have a maximum external quantum efficiency of 2.62% and a half lifetime (T₅₀) of 8.8 min. Meanwhile, the electroluminescence spectrum with its peak located at 485 nm, demonstrates improved stability by applying different voltage bias. The finding in this work offers a new way to achieve steady blue PeLEDs with high performance.     

Efficient Blue Perovskite Light‐Emitting Diodes Boosted by 2D/3D Energy Cascade Channels

Lead halide perovskite, as an emerging semiconductor, provides a fire‐new opportunity for high‐definition display and solid‐state lighting. Earthshaking improvements are implemented in green, red, and near‐infrared perovskite light‐emitting diodes (PeLEDs). However, blue PeLEDs are still far behind in performance, which restricts the development of PeLEDs in practical applications. Herein, a facile energy cascade channel strategy via one‐step self‐organized and controllable 2D/3D perovskite preparation by introducing guanidine hydrobromide (GABr) is developed that greatly improves the efficiency of blue PeLEDs. The 2D/3D perovskite structure boosts the energy cascade to induce energy transfer from the wide into the narrow bandgap domains and inhibit free charge diffusion, which increases the density of electrons and holes, and enhances the radiative recombination. Profiting from this energy cascade channels, the external quantum efficiency of blue PeLEDs, emitting at 492 nm, is considerably enhanced from 1.5% of initial blue device to 8.2%. In addition, device operating stability under ambient conditions is also improved by 2.6‐fold. The one‐step self‐organized 2D/3D hybrid perovskites induced by GABr pave a new and simple route toward high‐performance blue emission PeLEDs.     

The Trapped Charges at Grain Boundaries in Perovskite Solar Cells

The performance of perovskite solar cells is greatly affected by the crystallization of the perovskite active layer. Perovskite crystal grains should neatly arrange and penetrate the entire active layer for an ideal perovskite crystallization. These kinds of crystallized perovskite films exhibit fewer defects and longer carrier lifetime, which is beneficial to enhance the performance of perovskite solar cells. Here, by testing the residual charge of perovskite solar cells with different crystallization conditions, it is demonstrated that the residual charge exists widely at the grain boundary, which is parallel to the device, and the residual charge is related to the performance of the perovskite solar cells. Single crystal grains neatly arranged and penetrate the entire active layer can generate less residual charge and improve device performance of the perovskite solar cells. The results also show that the long decay time of open-circuit voltage comes from the detrapping of trapped carriers. The residual charge testing technology provides a new idea for the investigation of carrier trap and detrap characteristics in photovoltaic devices.     

Working Principles of Perovskite Photodetectors: Analyzing the Interplay Between Photoconductivity and Voltage‐Driven Energy‐Level Alignment

Organic–inorganic lead halide perovskites have recently received significant attention as active materials for high‐performance photovoltaics and photodetectors. However, the understanding of their operation mechanism remains limited. High‐gain, low‐voltage CH₃NH₃PbI₃ photodetectors in various architectures are demonstrated herein. Photomultiplication in all structures with direct contact of fluorine‐doped tin oxide (FTO) and perovskite with the highest responsivity 208 A W^?1 corresponding to an incident photon‐to‐current efficiency of 47 000% is observed. Studying the dynamics and temperature dependence, a slow process with an activation energy of 420 ± 90 meV in the time scale of seconds is found, which is essential to photocurrent multiplication. A model based on ion migration to explain the observed transients and the photomultiplication is developed. The accumulation of negative ionic charge at the FTO/perovskite interface under reverse bias lowers the FTO work function allowing for direct hole injection into the perovskite valence band. Under illumination, the conductivity of perovskite is increased and the device behaves similar to a photoconductor.     

Synthesis of 0D Manganese-Based Organic–Inorganic Hybrid Perovskite and Its Application in Lead-Free Red Light-Emitting Diode

Lead-based perovskite light-emitting diodes (PeLEDs) have exhibited excellent purity, high efficiency, and good brightness. In order to develop nontoxic, highly luminescent metal halide perovskite materials, tin, copper, germanium, zinc, bismuth, and other lead-free perovskites have been developed. Here, a novel 0D manganese-based (Mn-based) organic–inorganic hybrid perovskite with the red emission located at 629 nm, high photoluminescence quantum yield of 80%, and millisecond level triplet lifetime is reported. When applied as the emissive layer in the PeLEDs, the maximum recording brightness of devices after optimization is 4700 cd m⁻², and the peak external quantum efficiency is 9.8%. The half-life of the device reaches 5.5 h at 5 V. The performance and stability of Mn-based PeLEDs are one order of magnitude higher than those of other lead-free PeLEDs. This work clearly shows that the Mn-based perovskite will provide another route to fabricate stable and high-performance lead-free PeLEDs.     

Interfacial Potassium-Guided Grain Growth for Efficient Deep-Blue Perovskite Light-Emitting Diodes

Perovskite light-emitting diodes (PeLEDs) are emerging candidates for the applications of solution-processed full-color displays. However, the device performance of deep-blue PeLED still lags far behind that of their red and green counterparts, which is largely limited by low external quantum efficiency (EQE) and poor operational stability. Here, a facile and reliable crystallization strategy for perovskite grains is proposed, with improved deep-blue emission through rational interfacial engineering. By modifying the substrate with potassium cation (K⁺) as the supplier of heterogeneous nucleation seeds, the interfacial K⁺-guided grain growth is realized for well-packed perovskite assemblies with high surface coverage and the controlled crystal orientation, leading to the enhanced radiative recombination and hole-transport capabilities. Synergistical boost in device performance is achieved for deep-blue PeLEDs emitting at 469 nm with a peak EQE of 4.14%, a maximum luminance of 451 cd m^–2, and spectrally stable color coordinates of (0.125, 0.076) that matches well with the National Television System Committee (NTSC) standard blue.     

Recent Progress on Synthesis,Intrinsic Properties and Optoelectronic Applications of Perovskite Single Crystals

Metal halide perovskite have shown great potential for applications in photovoltaics, light-emitting diodes and photon detectors, mainly owing to their superb optoelectronic properties, low-cost raw materials and facile fabrication process. Although, polycrystalline perovskite thin-films have been actively investigated for preparing various optoelectronic devices, the presence of detrimental defects at grain boundaries, serious ion migration and limited stability unfortunately hinder their device performance and practical application. As a contrast, perovskite single crystals (SCs) exhibit no grain boundaries, much lower trap density and much improved stability, hence providing a more attractive choice for not only optoelectronic device applications but also fundamental research. In this review, recent progress in the growth methods of perovskite SCs is summarized, followed by giving a detailed introduction of the intrinsic properties of perovskite SCs including optical properties, defects, charge carrier dynamics, ion migration and stability. On these base, the applications of perovskite SCs in various optoelectronic devices like solar cells, photodetectors, and radiation detectors are discussed, where the relationship between the composition, device architecture and device performance is highlighted. Finally, a tentative discussion on the current challenges and future opportunities in the development of perovskite SCs and optoelectronic devices is presented.     

Solution‐Processed Flexible Broadband Photodetectors with Solution‐Processed Transparent Polymeric Electrode

Room‐temperature solution‐processed flexible photodetectors with spectral response from 300 to 2600 nm are reported. Solution‐processed polymeric thin film with transparency ranging from 300 to 7000 nm and superior electrical conductivity as the transparent electrode is reported. Solution‐processed flexible broadband photodetectors with a “vertical” device structure incorporating a perovskite/PbSe quantum dot bilayer thin film based on the above solution‐processed transparent polymeric electrode are demonstrated. The utilization of perovskite/PbSe quantum dot bilayer thin film as the photoactive layer extends spectral response to infrared region and boosts photocurrent densities in both visible and infrared regions through the trap‐assisted photomultiplication effect. Operated at room temperature and under an external bias of ‐1 V, the solution‐processed flexible photodetectors exhibit over 230 mA W^‐1 responsivity, over 1011 cm Hz1/2/W photodetectivity from 300 to 2600 nm and ≈70 dB linear dynamic ranges. It is also found that the solution‐processed flexible broadband photodetectors exhibit fast response time and excellent flexibility. All these results demonstrate that this work develop a facile approach to realize room‐temperature operated ultrasensitive solution‐processed flexible broadband photodetectors with “vertical” device structure through solution‐processed transparent polymeric electrode.     

A rapid annealing technique for efficient perovskite solar cells fabricated in air condition under high humidity

A rapid annealing technique for fabricating perovskite materials via microwave radiation in air condition is presented. A planar-heterojunction perovskite device via microwave radiation within 6 min exhibits an efficiency of 10.29%, compared to 11.08% for a 90 min heating-annealed device in inert atmosphere, which is higher than that (8.04%) of a heating-annealed device in air condition under high humidity (∼60%). We believe that the microwave annealing technique provides a fast and less energy-intensive process for fabricating ideal perovskite active layers for high performance solar cells.     

浴铜灵有机分子材料对钙钛矿薄膜表面的钝化作用

采用2,9-二甲基-4,7-二苯基-1,10-邻二氮杂菲(浴铜灵,缩写:BCP)有机小分子作为钙钛矿薄膜与电子传输层之间的界面修饰层,从而使得反型结构的钙钛矿太阳电池性能得到显著改善。通过扫描电子显微镜研究发现:BCP分子可在钙钛矿薄膜样品表面的晶界间充分填充,推测其抑制了界面缺陷态的产生。进一步研究器件内部界面电荷的累积,并结合交流阻抗谱的分析,证实经BCP钝化的钙钛矿太阳电池中界面电荷的累积减少,光生载流子的复合被抑制,电池的光电转换效率由原来的15.7%提升到了17.4%。     

Precisely Controlled Hydration Water for Performance Improvement of Organic–Inorganic Perovskite Solar Cells

Recently, intensive studies on the role of water molecule in the formation of organic–inorganic perovskite film have been reported. However, not only the contradictive phenomena but also the complex processing technique has hindered the widespread use of water molecule in perovskite preparation. Here the hydration water is introduced into the precursors instead of water. By precisely controlling the content of hydration water, a smoother and more uniform perovskite film is obtained through a simple one‐step spin coating method. The improvement of perovskite film quality leads to highly efficient planar perovskite solar cells. Summing up the device studies and the investigation of morphology, crystallization, and optical properties, the impact of water molecule in the formation of perovskite crystal and consequences of device performance is understood. Due to its universal adaptability and simplified process, precise control of hydration water is therefore of great utility to high quality perovskite films fabrication and large‐scale production of this upcoming photovoltaic technology.     

Ultrathin perovskite based solar cells with the efficiency enhanced by charge transfer process

We report a new approach of improving the solar cells efficiency based on ultrathin perovskite films. We propose the addition of CuPc compound to perovskite active layer for enhanced charge generation and transfer process by charge transfer process between CuPc and perovskite. The performance of the devices with and without addition of CuPc was studied in respect to thickness of the active layer. The thickness was varied by the change of the spin coating speed in the range of 4000, 7000 and 10000 rpm, different concentration of CuPc also been studied. The process of charge carrier recombination, crystallinity and Raman characteristics of the obtained films was studied. The perovskite device with an active layer of MAPbI₃ mixed with CuPc spin coated with the speed of 10000 rpm with thickness of about 150 nm demonstrated the efficiency of 12.7%. The ultrathin mixed perovskite film (10000 rpm perovskite film of 15% CuPc) based device presents 33% thickness and 85% efficiency of common pure perovskite device (4000 rpm pure perovskite film).     

Hystersis mechanism in perovskite photovoltaic devices and its potential application for multi-bit memory devices

The hysteresis in perovskites devices puzzled researchers because it was a big hurdle for device stability and the origin of it was still a riddle for people to solve. Here we reported our analysis in mechanism of the hysteresis based on the trap states in the perovskites film surface. We tried to explain the current hysteresis through the dynamic charge trapping–detrapping processes and the conclusion applied both in porous and planar structure devices. However, the proportion of deep traps and shallow traps are different in planar structure device and in porous structure device. Furthermore, we found perovskite devices has potentials of serving as memory devices due to the photocurrent hysteresis. The on/off ratio of memory based on perovskite can be higher than 60 and the write time was as low as 0.54 s as memory. It also had a very low read bias near 0 V. Moreover, the devices show multi-bit property and a multi-bit organic memory came forward as a novel application of perovskite devices.     

Ultrahigh‐Performance Flexible and Self‐Powered Photodetectors with Ferroelectric P(VDF‐TrFE)/Perovskite Bulk Heterojunction

Flexible and self‐powered perovskite photodetectors attract widespread research interests due to their potential applications in portable and wearable optoelectronic devices. However, the reported devices mainly adopt an independent layered structure with complex fabrication processes and high carrier recombination. Herein, an integrated ferroelectric poly(vinylidene‐fluoride‐trifluoroethylene) (P(VDF‐TrFE)) and perovskite bulk heterojunction film photodetector on the polyethylene naphthalate substrate is demonstrated. Under the optimum treatment conditions (the polarization voltage and time, and the concentration of P(VDF‐TrFE)), the photodetector exhibits a largely enhanced performance compared to the pristine perovskite device. The resulting device exhibits ultrahigh performance with a large detectivity (1.4 × 10¹³ Jones) and fast response time (92/193 µs) at the wavelength of 650 nm. The improved performance is attributed to the fact that the polarized P(VDF‐TrFE)/perovskite hybrid film provides a stronger built‐in electric field to facilitate the separation and transportation of photogenerated carriers. These findings provide a new route to design self‐powered photodetectors from the aspect of device structure and carrier transport.     

单边凹槽电极结构MSM型蓝光探测器的研究

为提升InGaN基可见光探测器性能,制作并测试了基于GaN/InGaN MQWs外延材料的单边凹槽叉指电极MSM结构蓝光光电二极管。凹槽电极器件的I-V特性测试结果显示,相较于传统平面电极器件,随着偏压增加,器件暗电流越小且越趋于平缓,而光电流越大;光谱响应率测试显示,器件截止带边都位于490nm附近,凹槽电极器件带边处拒绝比高于平面电极器件1个量级。当偏压为5V时,凹槽电极器件响应率为0.0346A/W@480nm,对应外量子效率为8.94%,高于平面电极器件。器件性能提升的原因是单边凹槽电极结构有效改善了内建电场的分布,从而抑制了表面传导漏电流,使得器件暗电流更小且更有利于电极收集光生载流子,提升了响应率。