基于芳香族配体的二维钙钛矿太阳能电池研究进展

近年来，钙钛矿太阳能电池（PSCs）的效率得到了快速的发展，目前已经获得25.7%的认证效率，可与硅基太阳能电池相媲美。然而，PSCs的稳定性却远不如硅基太阳能电池，这限制了PSCs的使用。与此同时，二维（2D）或准二维钙钛矿材料受到了越来越多的关注，主要是因为大体积有机配体的引入明显地改善了材料的结构和环境稳定性。在2D PSCs领域，有机配体离子的设计和选择会直接影响材料的光电性能和器件的效率。目前，2D PSCs中所使用的有机配体主要分为脂肪族配体和芳香族配体。芳香族配体由于具有较大的介电常数、改善的电荷传输和可调控的组装结构等优点得到越来越多的关注。本文系统地总结了芳香族配体材料对2D钙钛矿性能的影响及其在2D PSCs领域的应用。     

石墨烯衍生物作为有机太阳能电池界面材料的研究进展

本文综述了石墨烯及其衍生物作为界面材料在有机太阳能电池中的应用, 包括作为阳极界面层、阴极界面层和叠层电池中间层等方面. 氧化石墨烯由于较好的透光性, 易于分散在水溶液中与溶液加工等优点已被应用在有机太阳能电池中. 对氧化石墨烯作为阳极界面层的研究包括通过部分还原或掺杂提高其导电性、通过引入高负电性原子提高其表面功函数, 以及通过与其他材料复合提高性能等. 同时, 本文综述了石墨烯衍生物及复合材料作为有机太阳能电池阴极界面层和叠层电池中间层的研究. 最后本文展望了石墨烯及其衍生物在有机太阳能电池与有机无机复合钙钛矿太阳能电池中的应用前景.     

钙钛矿太阳能电池中电子传输材料的研究进展

有机-无机杂化的卤素钙钛矿材料在2009年首次应用在光伏器件中, 而后有关此类型太阳能电池的报道数量呈井喷式增长. 至2014年5月钙钛矿电池光电转化效率已接近20%, 已超过有机及染料敏化太阳能电池的效率, 且有望达到单晶硅太阳能的水平, 成为光伏发电领域中的希望之星. 在钙钛矿电池中, 电子传输材料与吸收层的电子选择性接触对提高光电转化效率起到重要作用, 尤其在正置结构器件中, 电子传输层的介观结构直接影响钙钛矿的生长情况. 同时, 电子传输层的化学性质及其界面也会对电池的稳定性和寿命产生影响. 本文总结了电子传输材料在该类电池中的研究现状和热点, 并按材料的化学组分不同, 将电子传输材料分为三类: 金属氧化物、有机小分子和复合材料, 详细地介绍了电子传输材料在钙钛矿太阳能电池中的作用和近来的最新进展.     

钙钛矿太阳能电池近期进展

近几年来,基于有机无机金属卤化物钙钛矿(ABX_3)的太阳能电池由于其独特的物理化学性质受到了广泛的关注.这种钙钛矿材料具有很高的消光系数、较强的电荷传递能力、长的载流子寿命、长的载流子扩散距离以及特殊的双极性,同时低成本易制作.自2009年至今,钙钛矿太阳能电池的光电转换效率从最初的3.8%增长到了20.8%,使之成为最有可能在未来代替传统单晶硅太阳能电池的新型太阳能电池.同时,由于钙钛矿具有双极性,故钙钛矿太阳能电池的结构也有多种,最常见的结构有介孔结构、平面结构、介观超结构、无空穴传输层结构等.本文主要介绍钙钛矿太阳能电池的发展、电池结构及其对光电池性能的影响、钙钛矿薄膜的制备方法,同时探讨了钙钛矿在电子传输层上的吸附模型和电荷在电池界面中的传输机理以及界面工程,并介绍该类型电池在近期所获得的突破及未来可能的发展方向,以便对钙钛矿太阳能电池有进一步的了解.     

表面等离子激元与F-P共振耦合平衡钙钛矿太阳能电池有源层内载流子产生速率

为提高有机-无机杂化钙钛矿太阳能电池（PSCs）光吸收效率、平衡有源层中载流子产生速率,将周期性纳米光栅结构引入到PSCs器件结构中。分析了光栅周期、光栅高度和有源层厚度对表面等离子激元（SPPs）与法布里-珀罗（F-P）共振耦合模式的影响。通过改变光栅周期,实现了SPPs与F-P共振耦合波长范围与钙钛矿材料的弱吸收光谱区域相重合,同时光栅高度的增加可以增大耦合模式的光谱宽度。SPPs与F-P共振耦合模式实现了金属电极与电子传输层（ETL）界面处的局域电场增强。结果表明:场增强效应扩展到有源区,有效提高了PSCs有源层远入射光侧在570~800 nm波长范围内的光吸收,进而提高了有源层远入射光区域的载流子产生速率。当光栅周期为250 nm、光栅高度为50 nm、源层厚度为300 nm时,PSCs在太阳光弱吸收光谱区域内的本征吸收提高了~12%,有源层远入射光侧载流子产生速率提高了~41%。     

分步磁控溅射ZnO和/或功能化碳纳米粒子修饰ZnO电子传输层增强聚合物太阳能电池效率

氧化锌具有良好电子传输性和高透光性,ZnO作为电子传输层已被广泛应用于聚合物太阳能电池。但采用溶胶凝胶法和真空镀膜制备ZnO电子传输层,因ZnO界面具有大量缺陷,极大增加载流子复合。抑制ZnO界面复合电流和改善ZnO界面接触性能,是提高ZnO基电子传输层聚合物太阳能电池性能关键所在。基于P3HT:PCBM反转型聚合物太阳能电池,采用磁控溅射ZnO层,研究了离子液功能化碳纳米粒子(ILCNs)修饰层或Ar/O₂混合气体溅射沉积ZnO修饰层,以及Ar/O₂溅射ZnO界面层与ILCNs联合修饰ZnO界面的聚合物太阳能电池性能。纯Ar和Ar/O₂混合气体下一步溅射沉积ZnO电子传输层,其电池效率分别为2.2%和2.8%。经ILCNs修饰或Ar/O₂溅射ZnO修饰层,电池效率分别达到3.4%和3.1%,并且分步溅射ZnO层并联合ILCNs修饰ZnO界面,聚合物太阳能电池效率可提高到3.8%。ZnO修饰型聚合物太阳能电池克服了电化学阻抗负阻效应,降低了反向暗电流并显示出更好的整流特性。研究表明,采用ILCNs修饰ZnO层和分步溅射ZnO层能有效抑制ZnO界面缺陷和改善界面接触性能,而采用分步溅射ZnO层与ILCNs联合修饰ZnO界面,这种联合修饰ZnO界面方案,更能增强ZnO层电子传输和提取能力,是提高聚合物太阳能电池效率更为有效方案。     

NaTFSI界面修饰对平面TiO2基钙钛矿太阳能电池的影响

在钙钛矿太阳能电池(PSCs)中,光吸收钙钛矿层夹在电子传输层(ETL)和空穴传输层(HTL)之间。钙钛矿层与电荷传输层之间的界面复合被认为是诱发器件电压损失的主要原因。通过对电荷传输层的修饰,不仅可以提高其电荷传输性能,而且还可以钝化界面缺陷,从而提高电池的光电转换效率(PCE)和稳定性。通过在平面二氧化钛层上引入一层双(三氟甲基磺酰基)亚胺钠(NaTFSI)来修饰二氧化钛ETL和钙钛矿之间的界面。实验结果显示,利用NaTFSI界面层修饰二氧化钛ETL不仅可以增大上层钙钛矿晶粒尺寸大小,减少晶界从而降低界面载流子复合;而且NaTFSI修饰后的ETL导电性增强,功函数降低。最后,通过优化NaTFSI界面层,实现了器件效率从18.62%至19.83%的显著提升。     

NaTFSI界面修饰对平面TiO_(2)基钙钛矿太阳能电池的影响EI北大核心CSCD

在钙钛矿太阳能电池(PSCs)中,光吸收钙钛矿层夹在电子传输层(ETL)和空穴传输层(HTL)之间。钙钛矿层与电荷传输层之间的界面复合被认为是诱发器件电压损失的主要原因。通过对电荷传输层的修饰,不仅可以提高其电荷传输性能,而且还可以钝化界面缺陷,从而提高电池的光电转换效率(PCE)和稳定性。通过在平面二氧化钛层上引入一层双(三氟甲基磺酰基)亚胺钠(NaTFSI)来修饰二氧化钛ETL和钙钛矿之间的界面。实验结果显示,利用NaTFSI界面层修饰二氧化钛ETL不仅可以增大上层钙钛矿晶粒尺寸大小,减少晶界从而降低界面载流子复合;而且NaTFSI修饰后的ETL导电性增强,功函数降低。最后,通过优化NaTFSI界面层,实现了器件效率从18.62%至19.83%的显著提升。     

材料设计以及界面与器件工程最适化以实现高性能聚合物和钙钛矿太阳能电池

有机聚合物和钙钛矿杂化物在合成控制、加工及属性调控的进展显著地增强了其太阳能电池性能。聚合物和杂化太阳能电池的性能十分依赖材料吸收光子、激子离解、电荷传输以及在金属/有机/金属氧化物或金属/钙钛矿/金属氧化物界面的电荷收集的效率。介绍了如何通过有效地整合材料设计以及界面与器件工程以显著提高聚合物和杂化钙钛矿型太阳能电池性能(转换效率>18%)。还介绍了一些关于制备串联和半透明太阳能电池的新型器件结构和光学工程策略,以发挥聚合物和钙钛矿太阳能电池的最大潜能。     

MAPbI_(3-x)Br_x钙钛矿薄膜中溴梯度对界面电荷转移的促进作用（英文）

混合卤素钙钛矿由于具有优异的光物理性质成为了光电子领域应用中的明星材料.因此,钙钛矿材料中光生载流子动力学的探究和调控对于进一步提升材料的性能具有重要意义.本文通过表面离子交换法制备了具有溴梯度的MAPbI_(3-x)Br_x钙钛矿薄膜,并对其内部载流子传输及界面电荷转移动力学过程进行了系统的研究.在MAPbI_(3-x)Br_x薄膜中,溴离子梯度分布所导致的能带梯度能有效促进光生空穴在薄膜内部的传输过程及在界面的提取过程.同时,由于卤素离子交换的后处理方法对薄膜表面起到了修饰作用,薄膜界面处的本征电子转移速率也得到了显著的提升.研究表明,在通过表面后处理方法制备的混合卤素钙钛矿薄膜中,有可能同时实现界面电子和空穴转移速率的提升,这对于进一步提升钙钛矿太阳能电池的能量转换效率具有一定的启发作用.     

TiO2/SnO2 electron transport double layers with ultrathin SnO2 for efficient planar perovskite solar cells

The electron transport layer (ETL) plays an important role on the performance and stability of perovskite solar cells (PSCs). Developing double ETL is a promising strategy to take the advantages of different ETL materials and avoid their drawbacks. Here, an ultrathin SnO₂ layer of ～ 5 nm deposited by atomic layer deposit (ALD) was used to construct a TiO₂/SnO₂ double ETL, improving the power conversion efficiency (PCE) from 18.02% to 21.13%. The ultrathin SnO₂ layer enhances the electrical conductivity of the double layer ETLs and improves band alignment at the ETL/perovskite interface, promoting charge extraction and transfer. The ultrathin SnO₂ layer also passivates the ETL/perovskite interface, suppressing nonradiative recombination. The double ETL achieves outstanding stability compared with PSCs with TiO₂ only ETL. The PSCs with double ETL retains 85% of its initial PCE after 900 hours illumination. Our work demonstrates the prospects of using ultrathin metal oxide to construct double ETL for high-performance PSCs.     

Electron transport layer engineering with rubidium chloride alkali halide to boost the performance of perovskite absorber layer

The mesoscopic perovskite solar cells (PSCs) based on titanium oxide (TiO₂) with a certified 25.2% efficiency are the forefront devices in the PSCs field. Hence, it can conclude the mesoporous titanium oxide (mp-TiO₂) is one of the most promising candidates to use as an electron transport layer (ETL) in PSCs. Improving the conductivity of mp-TiO₂ can consider as a simple route to motivate the electron extraction ability of this layer and increase the efficiency of PSCs. Herein, rubidium chloride (RbCl) was introduced as an additive source to boost the optoelectronic properties of mp-TiO₂ ETL. It was observed through ETL modification with RbCl, the optical transmittance of mp-TiO₂ remains constant but increases its electro-conductivity. Results showed that the morphology and crystalline properties of the perovskite layer with a modified ETL substrate is improved. It indicates a perovskite layer with enlarger grains and lower lead iodide (PbI₂) surplus. Altogether, ETL modification brings a champion efficiency of 11.10% for hole transport layer (HTL)-free PSCs higher than that of 8.65% for the HTL-free PSCs based on pristine ETL. Besides, Modified PSCs compared to pristine PSCs showed higher stability response as a result of lower grain boundaries in the modified perovskite layer.     

Anionic nonconjugated polyelectrolyte as an anode interfacial layer for polymer solar cells

Since the most high-performing donor polymers in polymer solar cells (PSCs) possessed the deep highest occupied molecular orbital (HOMO) level, interfacial engineering on anode contact is becoming increasingly important. Herein, we demonstrated efficient PSCs using an anionic poly(styrene sulfonate) (PSS) as an anode interfacial layer (AIL). With the formation of the dipole layer, the effective work function (WF) of indium tin oxide (ITO) electrode is significantly increased from 4.8 to 5.3 eV, providing favorable energetic alignment to the quasi-Fermi level of various donor polymers. Moreover, by incorporating cationic polyelectrolytes as a cathode interfacial layer, a pair of electric dipole layers induces a strong built-in electric field across the photoactive layer to drive efficient sweep-out of photogenerated charges. Consequently, the device with PSS AIL exhibited high power conversion efficiencies of 9.2 and 14.8% in PTB7-Th:PC₇₁BM- and PM6:Y6-based PSCs, respectively, both of which are higher than those of the devices with PEDOT:PSS.     

Ferroelectric Ba0.75Sr0.25TiO3 tunable charge transfer in perovskite devices

Interfacial charge recombination is a main issue causing the efficiency loss of the perovskite solar cells (PSCs). Here, ferroelectric Ba_0.75Sr_0.25TiO₃ (BST) is introduced as a polarization tunable layer to promote the interfacial charge transfer of the PSCs. The coexistence of ferroelectric polarization and charge carriers in BST is confirmed by density functional theory (DFT) calculations. Experimental characterization demonstrates the polarization reversal and the existence of domain in BST film. The BST film conductivity is tested as 2.98×10^-4 S/cm, which is comparable to the TiO₂ being used as the electron transporting layer (ETL) in PSCs. The calculations results prove that BST can be introduced into the PSCs and the interfacial charge transfer can be tuned by ferroelectric polarization. Thus, we fabricated the BST-based PSCs with a champion power conversion efficiency (PCE) of 19.05% after poling.     

Recent advances of interface engineering in inverted perovskite solar cells

Perovskite solar cells (PSCs) have witnessed great achievement in the past decade. Most of previous researches focus on the n—i—p structure of PSCs with ultra-high efficiency. While the n—i—p devices usually used the unstable charge transport layers, such as the hygroscopic doped spiro-OMeTAD, which affect the long-term stability. The inverted device with the p—i—n structure owns better stability when using stable undoped organic molecular or metal oxide materials. There are significant progresses in inverted PSCs, most of them related to charge transport or interface engineering. In this review, we will mainly summarize the inverted PSCs progresses related to the interface engineering. After that, we prospect the future direction on inverted PSCs.     

Low-temperature photo-activated inorganic electron transport layers for flexible inverted polymer solar cells

A simple and versatile route of forming sol–gel-derived metal oxide n-type electron transport layers (ETLs) for flexible inverted polymer solar cells (PSCs) is proposed using low-temperature photochemical activation process. The photochemical activation, which is induced by deep ultraviolet irradiation on sol–gel films, allows formation of metal oxide n-type ETLs such as zinc oxide (ZnO) and indium gallium zinc oxide films at a low temperature. Compared to poly(3-hexylthiophene)/phenyl-C₆₁-butyric acid methyl ester inverted PSCs with thermally annealed ZnO ETLs (optimized efficiency of 3.26 ± 0.03 %), the inverted PSCs with photo-activated ZnO ETLs showed an improved efficiency of 3.60 ± 0.02 %. The enhanced photovoltaic property is attributed to efficient charge collection from low overall series resistance and high surface area-to-geometric area ratio by the photo-activated ZnO ETLs.     

Enhancing light absorption for organic solar cells using front ITO nanograting and back ultrathin Al layer

To address the discrepancy between carrier collection and light absorption of organic solar cells caused by the limited carrier mobility and optical absorption coefficient for the normally employed organic photoactive layers, a light management structure composed of a front indium tin oxide(ITO) nanograting and ultrathin Al layer inserted in between the photoactive layer and the electron transport layer(ETL) is introduced. Owing to the antireflection and light scattering induced by the ITO nanograting and the suppression of light absorption in the ETL by the inserted Al layer, the light absorption of the photoactive layer is significantly enhanced in a spectral range from 400 nm to 650 nm that also covers the main energy region of solar irradiation for the normally employed active materials such as the P3HT:PC_(61) BM blend. The simulation results indicate that comparing with the control device with a planar configuration of ITO/PEDOT:PSS/P3HT:PC_(61) BM(80-nm thick)/Zn O/Al, the short-circuit current density and power conversion efficiency of the optimized light management structure can be improved by 32.86% and 34.46%. Moreover, good omnidirectional light management is observed for the proposed device structure. Owing to the fact that the light management structure possesses the simple structure and excellent performance, the exploration of such a structure can be believed to be significant in fabricating the thin film-based optoelectronic devices.     

High efficiency ETM-free perovskite cell composed of CuSCN and increasing gradient CH3NH3PbI3

To enhance device performance and reduce fabrication cost,a series of electron transporting material(ETM)-free perovskite solar cells(PSCs)is developed by TCAD Atlas.The accuracy of the physical mode of PSCs is verified,due to the simulations of PEDOT:PSS-CH₃NH₃PbI₃-PCBM and CuSCN-CH₃NH₃PbI₃-PCBM p-i-n PSCs showing a good agreement with experimental results.Different hole transporting materials(HTMs)are selected and directly combined with n-CH₃NH₃PbI₃,and the CuSCN-CH₃NH₃PbI₃ is the best in these ETM-free PSCs.To further study the CuSCN-CH₃NH₃PbI₃ PSC,the influences of back electrode material,gradient band gap,thickness,doping concentration,and bulk defect density on the performance are investigated.Energy band and distribution of electric field are utilized to optimize the design.As a result,the efficiency of CuSCN-CH₃NH₃PbI₃ PSC is achieved to be 26.64%.This study provides the guideline for designing and improving the performances of ETM-free PSCs.     

Microwave-reduced graphene oxide for efficient and stable hole extraction layers of polymer solar cells

Microwave-assisted reduced graphene oxide (MR-GO) layer was applied to hole extraction layer (HEL) of polymer solar cells (PSCs) and was compared with the widely used poly(3,4-ethylenedioxythiophene): poly(styrenesulfonate) (PEDOT:PSS) in bulk hetero-junction (BHJ) solar cells. The power conversion efficiency (PCE) of 3.57% was achieved with the MR-GO layer, which is 21% higher than that of PSCs with the conventional PEDOT:PSS HEL material. This enhancement of PCE is mainly attributed to the increase of short-circuit current density originated from the hydrophobic surface of the MR-GO layer. The hydrophobic graphene oxide surface is believed to improve wetting property and physical contact of active blends. In addition, the MR-GO interfacial layer is found to show the excellent device stability in atmospheric condition. The PCE of conventional PEDOT:PSS based PSCs showed total degradation when the device was exposed to atmospheric condition for 1000 h without any encapsulation, while that of MR-GO based PSC showed over 85% of PCE.