Jiarong Lian

Organic solvent vapor sensitive methylammonium lead trihalide film formation for efficient hybrid perovskite solar cells

The anisotropic electronic properties of the perovskite crystals originating from their non-cubic crystal structures can potentially give rise to the grain orientation correlated photovoltaic device performance. Here we report that an organic solvent vapor atmosphere introduced during the spin-coating and formation of perovskite films changes the orientation and size of perovskite grains. It was found that slightly larger but much more oriented methylammonium lead trihalide (CH3NH3PbI3) grains could be obtained under 1,2-dichlorobenzene (DCB) and dimethyl sulfoxide (DMSO) vapor atmospheres. The devices with more oriented grains outperformed regular devices with more random grains by a 50 mV larger open circuit voltage as well as a slightly increased fill factor. The device efficiency enhancement can be attributed to the longer charge recombination lifetime resulting from the reduced trap density and oriented grains. This result is important in providing guidelines for comparing the results from various groups because organic solvent vapors are generally present in a sealed glovebox for perovskite solar cell fabrication.

Film-through large perovskite grains formation via a combination of sequential thermal and solvent treatment

Organic–inorganic halide perovskites have recently attracted strong research interest for fabrication of high-performance, low-cost photovoltaic devices. Recently, we reported a highly reproducible procedure to fabricate high-performance organic–inorganic halide perovskite solar cells. This procedure, based on a one-step, solvent-induced, fast deposition-crystallization method, involves the use of sec-butyl alcohol as a new solvent to induce the CH3NH3PbI3 fast crystallization deposition. In the present study, we propose a reproducible fabrication method to prepare both flat and large-grain perovskite film by adding a pre-annealing step to strengthen the perovskite nucleation, aiming to facilitate the excess CH3NH3I and solvent removal in the sec-butyl alcohol soaking process, in which all films with thickness between 420 nm and 1 μm performed uniformly. The best performing planar device obtained with this procedure had an efficiency of 17.2% under AM 1.5G illumination and an average power conversion efficiency of 16.2 ± 0.5%. We also analyzed the efficiency of halide perovskite planar solar cells as a function of the perovskite film thickness; the efficiency dropped only slightly to 15.7% when the perovskite film thickness was increased to 1 μm.

sec-Butyl alcohol assisted pinhole-free perovskite film growth for high-performance solar cells

Perovskites have recently emerged as promising materials for high-performance, low-cost photovoltaic devices. Here, we report a one-step, solvent-induced, fast crystallization method based on sec-butyl alcohol to produce flat, uniform CH3NH3PbI3 films. sec-Butyl alcohol has proven to be a suitable solvent not only for the CH3NH3PbI3 fast crystallization deposition process, but also for adjusting the amount of CH3NH3I in CH3NH3PbI3 films. Planar heterojunction solar cells with flat and pinhole-free CH3NH3PbI3 films yielded an average power conversion efficiency (PCE) of 13.1 ± 1.2% and the highest PCE of 14.3%; no hysteresis was observed by changing the scan direction in our devices under standard AM 1.5 illumination. Remarkably, we found that the presence of CH3NH3I in CH3NH3PbI3 films has a positive effect on the photovoltaic device performance.

Synthesis, characterization and application of starburst 9-alkyl-1,3,6,8-tetraaryl-carbazole derivatives for blue-violet to UV OLEDs

A series of starburst carbazole derivatives, which comprise various aryl groups appended to the 1,3,6,8-positions of a 9-alkyl-carbazole core, are synthesized and characterized. These compounds exhibit good thermal stabilities with glass transition temperatures up to 199 °C and thermal decomposition temperatures ranging from 321 to 485 °C. The starburst configuration of the as-prepared compounds results in fluorescence emission in the UV to blue-violet region (λmax = 389–409 nm) with photoluminescence quantum efficiency (ΦPL) reaching 90% and narrow full width half maximum (FWHM) of 43–54 nm in solution. Light-emitting devices are successfully fabricated using these materials as emitters, and emit UV to blue-violet light. With a device structure of indium tin oxide (ITO)/molybdenum trioxide (MoO3)/1,3,6,8-tetraaryl carbazole derivatives/1,3,5-tris(2-N-phenylbenzimidazolyl)benzene (TPBI)/8-hydroxyquinoline aluminum (Alq3)/LiF/Al, maximum external quantum efficiency (EQEmax) of 2.05% and 3.4% have been obtained at UV wavelength of 394 nm with FWHM of 42 nm and blue-violet wavelength of 415 nm with FWHM of 46 nm, respectively.

Fabrication of high-performance and low-hysteresis lead halide perovskite solar cells by utilizing a versatile alcohol-soluble bispyridinium salt as an efficient cathode modifier

A novel alcohol-soluble conjugated bispyridinium salt (FPyBr) is developed and used as a cathode modifier to improve the cathode interface of planar heterojunction perovskite solar cells (PHJ PVSCs). The excellent electron-withdrawing ability of bispyridinium rings endows FPyBr with a favorable energy level alignment with phenyl-C60-butyric acid methyl ester (PCBM) and the cathode (e.g., Al), which leads to an ideal ohmic contact and efficient electron transport and collection. The deep-lying highest occupied molecular orbital energy level of FPyBr can also effectively block hole carriers and thus decrease leakage current and hole–electron recombination at the cathode interface. In addition, FPyBr can n-dope PCBM through an anion-induced electron transfer process, which increases the electron mobility of PCBM drastically, thereby diminishing interfacial resistance and promoting electron transport. As a result, by incorporating an FPyBr cathode interlayer with ethanol solvent, high-performance and low-hysteresis PHJ PVSCs with a maximal power conversion efficiency (PCE) of 19.61% can be realized. In contrast, reference devices without any cathode interlayer display a distinctly worse performance, with a PCE of 16.97%. Therefore, this excellent cathode modifier provides a new opportunity to fabricate high performance multilayer PVSCs using low-temperature solution processing without interfacial erosion/mixing.

Interfacial Layers in Organic Solar Cells

interfacial layers play a critical role in organic solar cells (OSCs) to determine their efficiency and lifetime. The introduction of proper interfacial materials at the both interfaces of charge separation and charge collection has become an important strategy to obtain high power conversion efficiency (PCE) and high-stability OSCs. In the past decade, considerable efforts have been devoted to the interface engineering of OSCs, and significant advancement has been made. Some of these progresses have been extensively reviewed in other reports. Herein we aim to give a deep understanding for each kind of interfacial materials, and to review the most recent advancements on the design and application of these materials. In this book chapter, we first summarized the functions of the interfacial layers OSCs to explain why they are needed in OSCs. Second, we reviewed the progress of interfacial material research based on their functions, including modifying charge separation and extraction in OSCs, engineering the morphology of active layer, adjusting light harvesting, and so on. Considering the absence of general interfacial layers design criteria available to device manufacturers, we made final thoughts and outlooks for the future development of interfacial study to conclude this chapter.

Improved performance of organic light emitting devices using triazole/ Cs2CO3/Al cathode

In this study, a new cathode system of triazole (TAZ)/Cs2CO3/Al has been proposed. Obvious efficiency improvement and sharp enhanced electron injection were maintained in the devices with this new cathode. TAZ owns deep the highest occupied molecular orbital (HOMO) and wide band gap, so as to block the hole leakage effectively and confine the exciton in Alq3 emissive layer. An abrupt lowering of the vacuum level was found in the mixture of TAZ and Cs2CO3, which indicated that the electron injection barrier from metal cathode into Alq3 was greatly reduced. Our experimental proved that this new cathode may have a wide application in OLEDs emitting light with short wavelength.

Interfacial Passivation of the p‐Doped Hole‐Transporting Layer Using General Insulating Polymers for High‐Performance Inverted Perovskite Solar Cells

Organic-inorganic lead halide perovskite solar cells (PVSCs), as a competing technology with traditional inorganic solar cells, have now realized a high power conversion efficiency (PCE) of 22.1%. In PVSCs, interfacial carrier recombination is one of the dominant energy-loss mechanisms, which also results in the simultaneous loss of potential efficiency. In this work, for planar inverted PVSCs, the carrier recombination is dominated by the dopant concentration in the p-doped hole transport layers (HTLs), since the F4-TCNQ dopant induces more charge traps and electronic transmission channels, thus leading to a decrease in open-circuit voltages (VOC ). This issue is efficiently overcome by inserting a thin insulating polymer layer (poly(methyl methacrylate) or polystyrene) as a passivation layer with an appropriate thickness, which allows for increases in the VOC without significantly sacrificing the fill factor. It is believed that the passivation layer attributes to the passivation of interfacial recombination and the suppression of current leakage at the perovskite/HTL interface. By manipulating this interfacial passivation technique, a high PCE of 20.3% is achieved without hysteresis. Consequently, this versatile interfacial passivation methodology is highly useful for further improving the performance of planar inverted PVSCs.

Semimetal-Semiconductor Transitions for Monolayer Antimonene Nanosheets and Their Application in Perovskite Solar Cells

Antimonene-based 2D materials are attracting increasing research interest due to their superior physicochemical properties and promising applications in next-generation electronics and optoelectronics devices. However, the semiconductor properties of antimonene are still at the theoretical simulation stage and are not experimentally verified, significantly restricting its applications in specific areas. In this study, the semiconductor properties of monolayer antimonene nanosheets are experimentally verified. It is found that the obtained semiconductive antimonene nanosheets (SANs) exhibit indirect bandgap properties, with photoluminescence (PL) bandgap at about 2.33 eV and PL lifetime of 4.3 ns. Moreover, the obtained SANs are ideal for the hole extraction layer in planar inverted perovskite solar cells (PVSCs) and significantly enhance the device performance due to fast hole extraction and efficient hole transfer at the perovskite/hole transport layer interface. Overall, these findings look promising for the future prospects of antimonene in electronics and optoelectronics.

Rational Solvent Annealing for Perovskite Film Formation in Air Condition (July 2017)

The past few years have witnessed a rapid growth in research and development activities for the emerging hybrid perovskite solar cells (PSCs), whose power conversion efficiencies have approached that of the commercialized silicon solar cells. In this regard, we try to develop a rational and accurately controllable solvent annealing method in air condition to maintain cost effective solar energy for PSCs. We have tailored the perovskite crystal growth process by optimizing dimethyl sulfoxide (DMSO) vapor annealing parameters, including the vapor concentration, the annealing time duration, and time point. The result shows that film-through large grains and sharply reduced surface defects can be obtained for perovskite film when the DMSO vapor annealing treatment is set at the initial stage of crystal growth, followed with mere thermal annealing for at least 20 min to reconstruct the perovskite crystal. Our results have supplied strong evidences for the scenario of perovskite film surface dissolution in DMSO vapor and the key role of atmosphere at the initial stage of crystal growth process for the final perovskite film morphology.