Effects of optical interference and annealing on the performance of poly(3-hexylthiophene):fullerene based solar cells

In this paper, the effects of optical interference and annealing on the performance of P3HT：PCBM based organic solar cells are studied in detail. Due to the optical interference effect, short circuit current density （Jsc） shows obvious oscillatory behaviour with the variation of active layer thickness. With the help of the simulated results, the devices are optimized around the first two optical interference peaks. It is found that the optimized thicknesses are 80 and 208 nm. The study on the effect of annealing on the performance indicates that post-annealing is more favourable than pre-annealing. Based on post-annealing, different annealing temperatures are tested. The optimized annealing condition is 160℃ for 10 min in a nitrogen atmosphere. The device shows that the open circuit voltage Voc achieves about 0.65V and the power conversion efficiency is as high as 4.0 % around the second interference peak.

An Unprecedented Efficiency with Approaching 21%Enabled by Additive‑Assisted Layer‑by‑Layer Processing in Organic Solar Cells

Recently published in Joule,Feng Liu and colleagues from Shanghai Jiaotong University reported a record-breaking 20.8%power conversion efficiency in organic solar cells(OSCs)with an interpenetrating fibril network active layer morphology,featuring a bulk p-in structure and proper vertical segregation achieved through additive-assisted layer-by-layer deposition.This optimized hierarchical gradient fibrillar morphology and optical management synergistically facilitates exciton diffusion,reduces recombination losses,and enhances light capture capability.This approach not only offers a solution to achieving high-efficiency devices but also demonstrates the potential for commercial applications of OSCs.

Influence of optical interference and carrier lifetime on the short circuit current density of organic bulk heterojunction solar cells

Based on simple analytical equations, short circuit current density （Jsc） of the organic bulk heterojunction solar cells has been calculated. It is found that the optical interference effect plays a very important role in the determination of Jsc; and obvious oscillatory behaviour of Jsc was observed as a function of thickness. At the same time, the influence of the carrier lifetime on Jsc also cannot be neglected. When the carrier lifetime is relatively short, Jsc only increases at the initial stage and then decreases rapidly with the increase of active layer thickness. However, for a relatively long carrier lifetime, the exciton dissociation probability must be considered, and Jsc behaves wave-like with the increase of active layer thickness. The validity of this model is confirmed by the experimental results.

Effect of Optical Microcavity on Absorption Behavior of Homo-Tandem Organic Solar Cells

The optical microcavity effect of the homo-tandem solar cells is explored utilizing the transfer matrix method. Ultrathin silver can reduce the deadzone effect compared with graphene and PH1000, and leads to a factor of 1.07 enhancement for an electrical field in a metal microcavity. The enhancement is considered to be the fact that strong exciton-photon coupling occurs in the microcavity due to ultrathin Ag. On the basis of the optical enhancement effect, optical behaviors are manipulated by varying the microcavity length. It is confirmed that ultrathin silver can serve as an ideal interconnection layer as the active layer is ～ 150nm thick and the thickness ratio between front and rear active layers lies between 1：1 and 1：2.

Significant Enhancement in Built-in Potential and Charge Carrier Collection of Organic Solar Cells using 4-（5-hexylthiophene-2-yl）-2,6-bis（5- trifluoromethyl）thiophen-2-yl）pyridine as a Cathode Buffer Layer

An electron transporting material of TFTTP （4-（5-hexylthiophene-2-yl）-2,6-bis（5-trifluoromethyl）thiophen-2-yl）pyridine） was investigated as a cathode buffer layer to enhance the power efficiency of organic solar cells （OSCs） based on subphthalocyanine and C60. The overall power conversion efficiency was increased by a factor of 1.31 by inserting the TFTTP interfacial layer between the active layer and metallic cathode. The inner mechanism responsible for the performance enhancement of OSCs was systematically studied with the simulation of dark diode behavior and optical field distribution inside the devices as well as the characterization of device photocurrent. The results showed that the TFTTP layer could significantly increase the built-in potential in the devices, leading to the enhanced dissociation of charge transfer excitons. In addition, by using TFTTP as the buffer layer, a better Ohmic contact at C60/metal interface was formed, facilitating more efficient free charge carrier collection.

A new nonfullerene acceptor with an extended π conjugation core enables ternary organic solar cells approaching 19%efficiency

In organic solar cells(OSCs),it is an effective way to improve the power conversion efficiency(PCE)by adding a guest component with appropriate absorption and energy levels in the host system.Herein,a new nonfullerene acceptor(NFA)named TBF-2Cl was developed by the strategy of expanding theπconjugated core of 2,2’-(((4,4,9,9-tetrahexyl-4,9-dihydro-s-indaceno[1,2-b:5,6-b’]dithiophene-2,7-diyl)bis(methaneylylidene))bis(5,6-dichloro-3-oxo-2,3-dihydro-1H-indene-2,1-diylidene))dimalononitrile(IDT-4Cl)with two benzene rings.With increase of benzene units,TBF-2Cl exhibits higher lowest unoccupied molecular orbital(LUMO)level of-3.75 eV than that of one benzene unit based NFA IDT-4Cl and fluorene core based NFA F-2Cl,which facilitates enhancing the open-circuit voltage(V_(oc))of ternary devices.Moreover,TBF-2Cl film shows a medium optical bandgap with the absorption range from 500-800 nm,being well complementary with the wide bandgap polymer donor D18 and narrow bandgap NFA CH-6F.Accordingly,a remarkable PCE of 18.92%with a high short-circuit current density(J_(sc))of 27.40 mA·cm^(-2),a fill factor(FF)of 0.749,especially an outstanding V_(oc) of 0.922 V was achieved for the optimal ternary device based on D18:TBF-2Cl:CH-6F,surpassing the binary counterpart(17.08%).The findings provide insight into the development of new guest acceptors for obtaining more efficient OSCs.

Investigation of post-thermal annealing-induced enhancement in photovoltaic performance for squaraine-based organic solar cells

In this work,we have systematically investigated the post-thermal annealing-induced enhancement in photovoltaic performance of a 2,4-bis[4-(N,N-diisobutylamino)-2,6-dihydroxyphenyl]squaraine(DIBSQ)/C60 planar heterojunction(PHJ)organic solar cells(OSCs).An increased power conversion efficiency(PCE)of 3.28%has been realized from a DIBSQ/C60 device with thermal annealing at 100°C for 4 min,which is about 33%enhancement compared with that of the as-cast device.The improvement of the device performance may be mainly ascribed to the crystallinity of the DIBSQ film with post-thermal annealing,which will change the DIBSQ donor and C60 acceptor interface from^PHJ to hybrid planar-mixed heterojunction.This new donor-acceptor heterojunction structure will significantly improve the charge separation and charge collection efficiency,as well as the open circuit voltage(Voc)of the device,leading to an enhanced PCE.This work provides an effective strategy to improve the photovoltaic performance of SQ-based OSCs.

Narrow bandgap molecular dyads incorporating Y-series acceptor backbones for efficient single-molecular organic solar cells

The performance of organic solar cells(OSCs)is mainly related to the bulk heterojunction(BHJ)microstructure of specific active layer systems,which is often in a metastable state.A promising strategy to address the abovementioned shortcomings of BHJs is to develop single-component active layer materials.Owing to the single-component small molecule materials with defined chemical structures generally exhibit poor absorption spectra,herein we first introduced narrow bandgap Y-series acceptors into the molecular skeleton of single-component materials,and designed two molecular dyads,SM-Et-1Y and SM-Et-2Y.The optical bandgaps(E_g~(opt)s)of the two dyads are 1.364 and 1.361 eV,respectively,which are much smaller than those of previously reported single-component molecules.Consequently,the SM-Et-2Y-based single-component OSCs(SCOSCs)showed a power conversion efficiency(PCE)of 5.07%,superior to SM-Et-1Y(2.53%),which is one of the highest PCEs reported for SCOSCs to date.Moreover,both SM-Et-1Y-and SM-Et-2Y-based devices exhibited excellent photo-stability,retaining over 90%of their initial performance after 250 h of continuous illumination.Our results provide a deeper understanding of the molecular backbone and a guiding principle for the rational design or selection of non-fullerene single-component materials with suitable donor/acceptor ratios.

Morphology optimization of photoactive layers in organic solar cells

Organic solar cells(OSCs)have unique advantages of light weight,low-cost solution processing,and capability to be fabricated into flexible and semitransparent devices,which are widely recognized as a promising photovoltaic technology.Photoactive layers of the OSCs are composed of a blend of a p-type organic semiconductor as a donor(D)and an n-type organic semiconductor as acceptor(A).The morphology of the active layer with D/A nano-scaled aggregation and face-onπconjugated packing,and D/A interpenetrating network is crucial for achieving high photovoltaic performance of the OSCs.Therefore,great efforts have been devoted to control and optimize morphology of the active layers.This perspective focuses on the morphological control by solvent/solid processing additives and the morphology optimization by postdeposition treatment with thermal annealing and/or solvent vapor annealing,which have been extensively adopted and exhibit promising positive effect in optimizing the morphology.Representative examples are given and discussed to understand the foundation of the postdeposition treatments on tuning the morphology.Insights into the role of the postdeposition treatments and additive treatments on the morphology optimization will be beneficial to further improvement in morphology optimization for practical organic photovoltaic application.

18.01%Efficiency organic solar cell and 2.53%light utilization efficiency semitransparent organic solar cell enabled by optimizing PM6:Y6 active layer morphology

Optimizing the photoactive layer morphology is a simple,promising way to improve the power conversion efficiencies(PCEs)of organic solar cells(OSCs).Here,we compared different post-processing treatments on PM6:Y6 blend films and relevant effects on device performances,including as-cast,thermal annealing and solvent annealing.This solvent annealing processes can effectively improve the vertical distribution and aggregation of polymer donors and small molecule acceptors,then optimize the active layer film morphology,ultimately elevating PCE.Thus,one of champion efficiencies of 18.01%was achieved based on the PM6:Y6 binary OSCs.In addition,a relatively high light utilization efficiency(2.53%)was achieved when a transparent electrode made of Cu(1 nm)and Ag(15 nm)was utilized to fabricate a semitransparent OSC with a remarkable PCE of 13.07%and 19.33%average visible-light transmittance.These results demonstrated that carefully optimizing morphology of active layer is conducive to achieving a high-performance OSC.

Semitransparent Flexible Organic Solar Cells

The semitransparent flexible organic solar cell takes advantages of flexibility,transparency,color adjust ment property,which is more conducive to integrate on buidings and mobile terminals.Ascribing to the developments of narrow band gap donors and the new non-fullerene acceptors,the power conversion efficiency of semitransparent flexible organic solar cells has been achieved 10% to 12% with average visible transmittance of 17% to 21%.This review summarizes the molecular design of the most representative layer materials,and discusses the characterization of semitransparent parameters paradigms,then we discuss how to optimize the device in combination with optical simulation,and finally list the recent development of semitransparent flexible electrodes of ITO-free organic solar cells,and give our perspectives on the next step direction.

The effect of annealing treatment on the performance of bulk heterojunction solar cells with donor and acceptor different weight ratios

Bulk heterojunction organic solar cells (OSCs) based on the blend of poly(2-methoxy-5(2′-ethyl-hexyloxy)-1,4-phenylenevinylene (MEH-PPV) and [6,6]-phenyl C61 butyric acid methyl ester (PCBM) with different weight ratios (from 1:3 to 1:5) have been fabricated and the effect of annealing treatment on the performance of OSCs has also been studied. Experimental results point to the best optimized doping concentration 1:4 for MEH-PPV:PCBM. Furthermore, it is found that the devices with annealing treatment at 150°C with 8 min show better performance compared with the devices without treatment. The series resistance (R s) is decreased, while the shunt resistance (R sh) increased by nearly 1.5 times. The short-circuit current density (J sc) and fill factor (FF) are improved by annealing treatment. As a result, the power conversion efficiency (PCE) of the devices increases from 0.49 % to 1.21 % with the ratio of 1:3 and from 1.09% to 1.42% with the ratio of 1:4.

Annealing-free alcohol-processable MoO_(X) anode interlayer enables efficient light utilization in organic photovoltaics

Molybdenum oxide(MoO_(x))is a commonly used hole extraction material in organic photovoltaics.The MoO_(x) interlayer is deposited typically via thermal evaporation in vacuum.To meet the need for rollto-roll manufacturing,solution processing of MoO_(x) without post-annealing treatment is essential.Herein,we demonstrate an effective approach to produce annealing-free,alcohol-processable MoO_(x) anode interlayers,namely S-MoO_(x),by utilizing the bis(catecholato)diboron(B_(2) Cat_(2))molecule to modify the surface oxygen sites in MoO_(x).The formation of surface diboron-oxygen complex enables the alcohol solubility of S-MoO_(x).An enhanced light utilization is realized in the S-MoO_(x)-based organic photovoltaics.This affords a superior short-circuit current density(Jsc)close to 26 mA cm^(-2) and ultimately a high power-conversion efficiency(PCE)of 15.2%in the representative PM6:Y6 based inverted OPVs,which is one of the highest values in the inverted OPVs using an as-cast S-MoO_(x) anode interlayer.

2D organic semiconductors, the future of green nanotechnology

The discovery of 2D organic semiconductors of atomically thin structures has attracted great attention due to their emerging optical, electronic, optoelectronic and mechatronic properties. Recent progress in such organic nanostructures has opened new opportunities for engineering material properties in many ways, such as, 0D/1D/2D nanoparticles hybridization, strain engineering, atomic doping etc. Moreover, 2D organic nanostructures exhibit a unique feature of bio–functionality and are highly sensitive to bio-analytes. Such peculiar behavior in 2D organics can be utilized to design highly-efficient bio-sensors. Also, a bio-molecular integrated electronic/optoelectronic device with enhanced performance can be attained. Furthermore, the bio-degradable, biocompatible, biometabolizable, non-toxic behaviour and natural origin of organic nanomaterials can address the current ecological concerns of increasing inorganic material based electronic waste. This review highlights the benefits of 2D organic semiconductors. Considering the importance of strategic techniques for growing thin 2D organic layers,this review summarizes progress towards this direction. The possible challenges for long-time stability and future research directions in 2D organic nano electronics/optoelectronics are also discussed. We believe that this review article provides immense research interests in organic 2D nanotechnology for exploiting green technologies in the future.

Recent progress in the numerical modeling for organic thin film solar cells

Device modeling is constructive in finding the dependency of devices efficiency on structure parameters and material properties. For the sake of looking into the physics mechanism of organic solar cells (OSCs), as well as predicting their maximum attainable efficiency, numerical modeling is widely utilized to simulate the behavior of OSCs. Although some indispensable parameters are neglected or hypothesized because of inexplicitness in simulation models for OSCs, numerical modeling can describe the kinetic process in OSCs intuitively. This paper summarizes the optical/electrical models in the BHJ solar cell, as well as addresses their corresponding development in recent years on the basis of device physics and its working principle. Applications of numerical modeling and comments on modeling results are summarized. Meanwhile, precision and open questions about every model are discussed.

Organic near-infrared optoelectronic materials and devices:an overview

Near-infrared(NIR)light has shown great potential for military and civilian applications owing to its advantages in the composition of sunlight,invisibility to human eyes,deeper penetration into biological tissues,and low optical loss in optical fibers.Therefore,organic optoelectronic materials that can absorb or emit NIR light have aroused great scientific interest in basic science and practical applications.Based on these NIR organic optoelectronic materials,NIR optoelectronic devices have been greatly improved in performance and application.In this review,the representative NIR organic optoelectronic materials used in organic solar cells,organic photodetectors,organic light-emitting diodes,organic lasers,and organic optical waveguide devices are briefly introduced,and the potential applications of each kind of device are briefly summarized.Finally,we summarize and take up the development of NIR organic optoelectronic materials and devices.

添加剂和溶剂退火协同优化制备高性能厚膜有机太阳能电池

通过溶剂添加剂1-氯萘(CN)和二硫化碳(CS_2)溶剂退火(SVA)协同优化了基于窄带隙小分子受体的厚膜活性层形貌,揭示了该策略对共混膜形貌的调控机理,研究了其对活性层中的载流子动力学以及器件光伏性能的影响.结果表明,CN添加剂可以有效促进受体材料结晶聚集,CS_2溶剂退火能够进一步提升活性层材料分子堆积的有序性,同时优化给受体材料相分离尺寸,降低共混膜表面的粗糙度,实现了良好的纳米尺寸相分离形貌.基于CN+SVA处理的PM6∶Y6厚膜(300 nm)器件的电荷传输和复合性质得到改善,取得了15.23%的光电转换效率(PCE),显著高于未经处理(PCE=11.75%)和仅用CN处理(PCE=13.48%)的光伏器件.该策略具有良好的适用性,将基于PTQ10∶m-BTP-PhC6器件的光伏性能从13.22%提升至16.92%.

高性能半透明有机太阳能电池的实现途径

半透明有机太阳能电池(STOSC)能够同时发电和透光,是极具应用前景的新能源技术,未来可应用于建筑物的窗户和屋顶实现光电建筑一体化,以及农业温室和交通工具等多种领域.然而,半透明电池的能量转换效率(PCE)和平均可见光透过率(AVT)的均衡调谐仍是一个问题.理想的高性能半透明有机太阳能电池需要平衡与提高AVT和PCE,即在选择性吸收和利用非可见光谱的光子转换为电能的同时,透过可见光谱区域光子实现透光,并保持良好的审美观感和颜色纯度.本文从活性层调控策略、器件工程和多功能STOSC等多个角度,讨论和总结了实现高性能STOSC的途径,为推进该技术的研究和发展提供有益的参考和建议.

半透明有机太阳能电池研究进展

半透明有机光伏(ST-OPVs)相比其它无机光伏技术,因为其活性层材料可调节的电子能级和选择性的吸收光谱,在作为温室的发电屋顶、现代建筑外墙和采光玻璃等应用中具有本征优势.随着高效窄带隙聚合物给体和近红外非富勒烯受体材料的快速发展, ST-OPVs的光利用效率在过去十年取得了显著进展,本征和具有光学修饰的半透明器件的光利用效率分别超过了3%和5%.为了进一步推动半透明有机光伏技术的实用化,进一步提升器件的光利用效率仍是研究重点.基于此,本文分别从半透明器件的理论模型、活性层材料设计和器件光学修饰等角度综合评述了近期ST-OPVs的重要进展,为未来器件性能的优化提供了参考.

卟啉类光电功能材料的研究进展

卟啉及其衍生物是一类具有优良的光电性能的有机半导体材料,引起人们广泛的关注。本文对卟啉类光电材料在模拟生物光合作用中心的光致电荷转移和能量转移,有机太阳能电池,分子光电器件,有机电致发光和光存储等领域的研究进展做一简要介绍。