Non-peripherally octaalkyl-substituted nickel phthalocyanines used as non-dopant hole transport materials in perovskite solar cells

This report presents two non-perihperally octaalkyl-substituted nickel phthalocyanines (NiPcs), namely, NiEt₂Pc and NiPr₂Pc, for use as dopant-free hole transport materials in perovskite solar cells (PSCs). The length extension of the alkyl chains from ethyl to propyl significantly tunes the NiPcs' energy levels, thus reducing charge carrier recombination at the perovskite/hole transport layer (HTL) interface and leading to higher open-circuit voltage (V_OC) and short-circuit current density (J_SC) observed for the NiPr₂Pc-based PSC. And higher charge carrier mobility, higher thin film crystallinity, and lower surface roughness of the NiPr₂Pc HTL compared with that of the NiEt₂Pc one also lead to higher J_SC and fill factor (FF) observed for the NiPr₂Pc-based device. Consequently, the NiPr₂Pc-based PSC exhibits a higher power conversion efficiency (PCE) of 14.07% than that of the NiEt₂Pc-based device (8.63%).     

Improving efficiency of inverted perovskite solar cells via ethanolamine-doped PEDOT:PSS as hole transport layer

In order to fabricate high-performance inverted perovskite solar cells (PeSCs), an appropriate hole transport layer (HTL) is essential since it will affect the hole extraction at perovskite/HTL interface and determine the crystallization quality of the subsequent perovskite films. Herein, a facile and simple method is developed by adding ethanolamine (ETA) into poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) as HTL. The doping of a low-concentration ETA can efficiently modify the electrical properties of the PEDOT:PSS film and lower the highest occupied molecular orbital (HOMO) level, which is more suitable for the hole extraction from the perovskite to HTL. Besides, ETA-doped PEDOT:PSS will create a perovskite film with larger grain size and higher crystallinity. Hence, the results show that the open-circuit voltage of the device increases from 0.99 V to 1.06 V, and the corresponding power conversion efficiency (PCE) increases from 14.68% to 19.16%. The alkaline nature of ethanolamine greatly neutralizes the acidity of PEDOT:PSS, and plays a role in protecting the anode, leading the stability of the devices to be improved significantly. After being stored for 2000 h, the PCE of ETA-doped PEDOT:PSS devices can maintain 84.2% of the initial value, which is much higher than 67.1% of undoped devices.     

Pentacene as a hole transport material for high performance planar perovskite solar cells

A cost-effective and efficient organic semiconductor pentacene was developed as a hole transport layer (HTL) material to replace classical PEDOT:PSS for planar perovskite solar cells (PSCs). As expected, the pentacene based device exhibits power conversion efficiency (PCE) of 15.90% (J_sc of 19.44 mA/cm², V_oc of 1.07 V, and FF of 77%), comparable to the PEDOT:PSS based device (PCE of 15.65%, J_sc of 18.78 mA/cm², V_oc of 1.07 V, and FF of 77%) under the same experimental conditions. The excellent performance of vacuum deposited pentacene is mainly attributed to the high efficient charge extraction and transfer in device due to the high-quality perovskite film grown on the top of pentacene substrate and a favorable energy-level alignment together with a desired downward band bending formed at the perovskite/pentacene interface. Our research has confirmed that pentacene could be served as a promising HTL material to achieve effective and potentially economical planar type PSCs.     

Enhanced efficiency and stability of polymer solar cells using solution-processed nickel oxide as hole transport material

Solution-processed nickel oxide (s-NiO_x) was synthesized for use as hole-transport layers (HTLs) in the fabrication of polymer solar cell (PSC) devices. The s-NiO_x thin-films were deposited using spin-coating and post-annealed at 300 °C, 400 °C, or 500 °C. With increased annealing temperature, the nickel acetate precursor decomposes more fully and forms s-NiO_x films that show larger crystalline grain sizes with lower root mean square surface roughness. Bulk heterojunction solar cells fabricated with the new random polymer RP(BDT-PDBT) and [6,6]-phenyl-C₇₀-butyric acid methyl ester (PC₇₀BM) using s-NiO_x as HTLs exhibit a 4.46% enhancement in power conversion efficiency and better stability compared to conventional PSCs using poly (3,4-ethylenedioxythiophene):poly(styrene sulfonate) as HTLs. We believe that the solution-processable and highly stable s-NiO_x could be a potential alternative for functional interface materials in optoelectronic devices.     

Charge transfer modification of inverted planar perovskite solar cells by NiOx/Sr:NiOx bilayer hole transport layer

Perovskite solar cells (PSCs) are the most promising commercial photoelectric conversion technology in the future. The planar p-i-n structure cells have advantages in negligible hysteresis, low temperature preparation and excellent stability. However, for inverted planar PSCs, the non-radiative recombination at the interface is an important reason that impedes the charge transfer and improvement of power conversion efficiency. Having a homogeneous, compact, and energy-level-matched charge transport layer is the key to reducing non-radiative recombination. In our study, NiO$_{x}$/Sr:NiO$_{x}$ bilayer hole transport layer (HTL) improves the holes transmission of NiO$_{x}$ based HTL, reduces the recombination in the interface between perovskite and HTL layer and improves the device performance. The bilayer HTL enhances the hole transfer by forming a driving force of an electric field and further improves $J_{\rm sc}$. As a result, the device has a power conversion efficiency of 18.44%, a short circuit current density of 22.81 mA$\cdot$cm$^{-2}$ and a fill factor of 0.80. Compared to the pristine PSCs, there are certain improvements of optical parameters. This method provides a new idea for the future design of novel hole transport layers and the development of high-performance solar cells.     

Highly efficient perovskite solar cells by tuning electronic structures of thienothiophene-based as hole transport materials

The atomic substitutions were used to study the hole transport materials (HTM) properties of six thiophenothiophene molecules (HTM1-HTM6) to reveal the relationship between their core structures and photoelectric properties. To better investigate the difference between experimentally original and designed molecules, we calculated the hole mobility and some parameters (such as energy levels, stability, and optical properties, etc). The results showed that the molecular orbital levels of the original and designed molecules have well matched with perovskite and Ag electrode to ensure hole transport and inhibit the electron reflux. Among the designed HTMs, HTM5 has the smallest energy gap that results in the red-shifted absorption spectra. Furthermore, there is an obviously increased charge transfer integral V due to the introduction of the Si atom, which greatly improved the hole mobility. Therefore, atom substitution by introducing Si atoms (HTM5) will improve the energy levels and charge transport ability, and molecular design by means of atom substitution can be a potential way to tunable HTM performance in solar cells.     

锡基钙钛矿太阳能电池载流子传输层的探讨

锡基钙钛矿太阳能电池可避免铅元素对环境带来的污染,近年来已成为光伏领域的研究热点.本文以SCAPS-1D太阳能电池数值模拟软件为平台,对不同电子传输层和不同空穴传输层的锡基钙钛矿太阳能电池器件的性能进行数值仿真对比,从理论上分析不同载流子传输层的锡基钙钛矿太阳能电池的性能差异.结果显示,载流子传输层与钙钛矿层的能带对齐...     

Enhanced stability of low temperature processed perovskite solar cells via augmented polaronic intensity of hole transporting layer

The commercial mass production of perovskite solar cells requires full compatibility with roll‐to‐roll processing with enhanced device stability. In line with this, the present work addresses following issues simultaneously from multiple fronts: (i) low temperature processed (140 °C) ZnO is used as electron transport layer (ETL) for fabricating the mixed organic cation based perovskite solar cells, (ii) the expensive hole transporting layer (HTL) spiro‐OMeTAD is replaced with F4TCNQ doped P3HT and (iii) the fabrication method does not incorporate the dopant TBP which is known to induce degradation processes in perovskite layer. All the devices under study were fabricated in ambient conditions. The F4TCNQ doped P3HT (HTL) based devices exhibits 14 times higher device stability compared to the conventional Li‐TFSI/TBP doped P3HT devices. The underlying mechanism behind the enhanced device lifetime in F4TCNQ doped P3HT (HTL) based devices was investigated via in‐depth electronic, ionic and polaronic characterization. The enhanced polaronic property in F4TCNQ doped P3HT HTL device ascertains its superior hole extraction and electron blocking capability; and consequently higher stability retained even after a month of ageing.

     

Impact of work function of back contact of perovskite solar cells without hole transport material analyzed by device simulation

The impact of the work function of a metal back contact on lead methylammonium tri-iodide based perovskite solar cells without hole transport material (HTM) was analyzed using device simulation. The elimination of the HTM is attractive in terms of the simplification of device structure and fabrication process. In the solar cell, a back junction is formed by the perovskite absorber and metal back contact. The device simulation revealed that the elimination of the HTM did not change the built-in voltage (V_bi) of the device when the work function of the metal back contact (?_M) was similar to the valence band maximum of the absorber (E_{v_absorber}). In the HTM-free structure, V_bi showed a high value if ?_M was equal to or deeper than E_{v_absorber}. In contrast, when ?_M was shallower than E_{v_absorber}, V_bi monotonically decreased, resulting in the decrease in open-circuit voltage of the device. The results showed the importance of the ?_M matching to maintain V_bi, which is useful guideline for the design of the HTM-free perovskite solar cells.     

Stabilization of formamidinium lead iodide perovskite precursor solution for blade-coating efficient carbon electrode perovskite solar cells

Formamidinium lead triiodide (FAPbI₃) is a research hotspot in perovskite photovoltaics due to its broad light absorption and proper thermal stability. However, quite a few researches focused on the stability of the FAPbI₃ perovskite precursor solutions. Besides, the most efficient FAPbI₃ layers are prepared by the spin-coating method, which is limited to the size of the device. Herein, the stability of FAPbI₃ perovskite solution with methylammonium chloride (MACl) or cesium chloride (CsCl) additive is studied for preparing perovskite film through an upscalable blade-coating method. Each additive works well for achieving a high-quality FAPbI₃ film, resulting in efficient carbon electrode perovskite solar cells (pero-SCs) in the ambient condition. However, the perovskite solution with MACl additive shows poor aging stability that no α-FAPbI₃ phase is observed when the solution is aged over one week. While the perovskite solution with CsCl additive shows promising aging stability that it still forms high-quality pure α-FAPbI₃ perovskite film even the solution is aged over one month. During the solution aging process, the MACl could be decomposed into methylamine which will form some unfavored intermediated phase inducing δ-phase FAPbI₃. Whereas, replacing MACl with CsCl could effectively solve this issue. Our founding shows that there is a great need to develop a non-MACl FAPbI₃ perovskite precursor solution for cost-effective preparation of pero-SCs.     

新型碳材料在钙钛矿太阳电池中的应用研究进展

新型碳材料如石墨烯及其氧化物、碳纳米管、富勒烯及石墨炔等因其优异的热学、力学、电学、光学性能成为了钙钛矿太阳电池研究的又一亮点. 本文总结了新型碳材料在钙钛矿太阳电池对电极、电子传输材料及空穴传输材料中的研究进展, 新型碳材料的引入有效地提高了钙钛矿电池的性能, 为下一步新型碳材料的应用开发以及钙钛矿电池器件的研究提供了新的思路.     

醋酸纤维素提高CsPbIBr2无机钙钛矿薄膜质量及其太阳能电池光电性能

由于具有适合的带隙和较高的稳定性,CsPbIBr₂无机钙钛矿被认为是一种较有前景的太阳能电池光吸收材料.但是目前报道的CsPbIBr₂钙钛矿太阳能电池效率还偏低,主要原因是制备的CsPbIBr₂钙钛矿膜质量差、缺陷多.本文通过将醋酸纤维素(CA)加入CsPbIBr₂钙钛矿前驱体溶液中改善CsPbIBr₂钙钛矿结晶过程,从而制备高质量的CsPbIBr₂钙钛矿膜.实验结果表明,CA中的C=O基团与前驱体溶液中的Pb²⁺间存在明显的相互作用,这种相互作用结合CA加入引起的前驱体溶液粘度增加,使CsPbIBr₂钙钛矿的结晶速率明显降低,从而制备了致密、结晶度高、晶粒尺寸大、晶界和缺陷少的高质量CsPbIBr₂钙钛矿膜.同时,CA的保护作用显著提高了CsPbIBr₂钙钛矿膜的稳定性.用碳材料层作为空穴传输层和背电极,制备结构为FTO/TiO₂/CsPbIBr...     

Fabrication of high-performance nickel/graphene oxide composite coatings using ultrasonic-assisted electrodeposition

Ultrasonic-assisted electrodeposition was used to fabricate the nickel/graphene oxide composite coatings with high hardness, low friction coefficient, and high wear resistance. In the present study, the effects of ultrasonic power and concentration of graphene oxide on the mechanical and tribological properties of the electrodeposited nickel/graphene oxide composite coatings were systematically studied. X-ray diffraction (XRD) analyses showed that the crystallite size of the nickel decreased with an increase of ultrasonic power (0–50 W, 40 KHz, square wave) and concentration of graphene oxide (0.1–0.4 g/L). Morphologies of the surface and cross-section of the composite coatings observed by Scanning Electron Microscopy (SEM) confirmed the existence of graphene oxide particles in the nickel matrix. The results from microhardness measurement demonstrated that the hardness was increased by 1.8 times using 50 W ultrasonic-assisted electrodeposition with the fixed concentration of graphene oxide (0.1 g/L), compared to the pure nickel coating. The hardness was increased by 4.4 times for the 0.4 g/L graphene oxide with the optimized ultrasonic power of 50 W in comparison to the pure nickel coating. Meanwhile, the friction coefficient decreased gradually with an increase in ultrasonic power and concentration of graphene oxide, respectively, where the effect of the concentration of graphene oxide played a more important role.     

Improving the performance of perovskite solar cells with glycerol-doped PEDOT:PSS buffer layer

In this paper, we investigate the effects of glycerol doping on transmittance, conductivity and surface morphology of poly(3,4-ethylene dioxythiophene):poly(styrene sulfonate))(PEDOT:PSS) and its influence on the performance of perovskite solar cells.. The conductivity of PEDOT:PSS is improved obviously by doping glycerol. The maximum of the conductivity is 0.89 S/cm when the doping concentration reaches 6 wt%, which increases about 127 times compared with undoped. The perovskite solar cells are fabricated with a configuration of indium tin oxide(ITO)/PEDOT:PSS/CH_3NH_3PbI_3/PC_(61)BM/Al, where PEDOT:PSS and PC_(61)BM are used as hole and electron transport layers, respectively. The results show an improvement of hole charge transport as well as an increase of short-circuit current density and a reduction of series resistance, owing to the higher conductivity of the doped PEDOT:PSS. Consequently, it improves the whole performance of perovskite solar cell. The power conversion efficiency(PCE) of the device is improved from 8.57% to 11.03% under AM 1.5 G(100 mW/cm~2 illumination) after the buffer layer has been modified.     

TiO_2 composite electron transport layers for planar perovskite solar cells by mixed spray pyrolysis with precursor solution incorporating TiO_2 nanoparticles

Perovskite solar cells with planar structure are attractive for their simplified device structure and reduced hysteresis effect. Compared to conventional mesoporous devices, TiO_2 porous scaffold layers are removed in planar devices. Then,compact TiO_2 electron transport layers take the functions of extracting electrons, transporting electrons, and blocking holes.Therefore, the properties of these compact TiO_2 layers are important for the performance of solar cells. In this work, we develop a mixed spray pyrolysis method for producing compact TiO_2 layers by incorporating TiO_2 nanoparticles with different size into the precursor solutions. For the optimized nanoparticle size of 60 nm, a power conversion efficiency of 16.7% is achieved, which is obviously higher than that of devices without incorporated nanoparticles(9.9%). Further investigation reveals that the incorporation of nanoparticles can remarkably improve the charge extraction and recombination processes.     

钙钛矿薄膜气相制备的晶粒尺寸优化及高效光伏转换

钙钛矿薄膜的气相制备是一种极具潜力的工业化生产工艺,但薄膜的质量控制目前远落后于溶液制备法.本文通过建立PbI_2薄膜向钙钛矿薄膜完全转化过程中反应时间、晶粒尺寸与温度的关系,实现了薄膜的质量优化及大面积钙钛矿薄膜的制备,将薄膜的平均晶粒粒径从0.42μm优化到0.81μm.基于空间电荷限制电流模型对缺陷密度的研究显示,钙钛矿薄膜的缺陷密度由5.90×10~(16)cm~(–3)降低到2.66×10~(16)cm~(–3).光伏器件(FTO/TiO_2/C_(60)/MAPbI_3/spiro-OMeTAD/Au结构)测试显示,面积为0.045cm~2器件的平均光电转换效率从14.00%提升到17.42%,最佳光电转换效率达到17.80%,迟滞因子减小至4.04%.同时,基于180℃制备的1cm~2器件的光电转换效率达到13.17%.     

Metal oxide buffer layer for improving performance of polymer solar cells

We report the application of aluminum doped ZnO (ZnO:Al) layer as a buffer on ITO glass for fabrication of non-inverted polymer solar cells. The ZnO:Al thin film was deposited using DC magnetron sputtering, with the thickness being varied from 23 to 100 nm. The devices showed most discernible improvements in their efficiencies when a thin layer of ZnO:Al film of thickness ∼40 nm was introduced. The observed enhancement in short circuit current density and open circuit voltage is likely attributed to the role of the ZnO:Al film as an optical tuner and an interfacial diffusion barrier. The result suggests that a metal oxide layer inserted between ITO and polymer layers can be a route for improving both efficiency and stability of polymer solar cells.     

高效无空穴传输层碳基钙钛矿太阳能电池的制备与性能研究

碳基钙钛矿太阳能电池因稳定性高、成本低廉而备受关注,但由于钙钛矿与碳电极之间能级匹配度不高,界面阻力大而导致效率不及金属基钙钛矿太阳能电池.本文制备了碳基无空穴传输层FTO/c-TiO₂/m-TiO₂/CH₃NH₃PbI₃/Carbon电池结构.通过对介孔二氧化钛层、钙钛矿层厚度进行优化,并对钙钛矿的薄膜形貌及钙钛矿激发电子寿命、可见光吸收度、载流子的提取与分离等进行深度分析,讨论了电池效率提升的内在机理.当介孔氧化钛层和钙钛矿层达到最优厚度时,钙钛矿太阳能电池获得了开路电压（V_oc）为0.93 V、电流密度（J_sc）为21.75 mA/cm²、填充因子为55%、光电转化效率达到11.11%.同时对电池进行了稳定性研究,在室温湿度为40%–50%的条件下放置15 d电池性能依旧稳定保持原来的95%,优于金属基钙钛矿太阳能电池,从而为碳电极钙钛矿太阳能电池的商业化发展提供了可能.     

n-Type microcrystalline silicon oxide layer and its application to high-performance back reflectors in thin-film silicon solar cells

Light trapping is a key issue in improving the efficiency of thin-film Si solar cells, and using a back reflector material plays a critical role in improving a cell's light-trapping efficiency. In this study, we developed n-type microcrystalline silicon oxide (n-μc-SiO_x) films that are suitable for use as back reflectors in thin-film silicon solar cells. They exhibit a lower refractive index and lower absorption spectra, especially at long wavelengths of >700 nm, than conventional ZnO:Al materials, which are beneficial for this application. The n-μc-SiO_x films were prepared by the PECVD (plasma-enhanced chemical vapor deposition) method and applied to the fabrication of back reflectors in μc-Si:H solar cells. We also characterized the changes in cell performance with respect to the refractive index, conductivity, and thickness of the n-μc-SiO_x back reflectors. The novel back reflector boosts the total current density by up to 3.0% with the help of the enhanced long-wavelength response. It also improves open circuit voltage (V_oc) and fill factor (FF), which may be attributed to the reduced shunt current caused by the anisotropic electrical characteristics of the n-μc-SiO_x layer. Finally, we could achieve a conversion efficiency for the hydrogenated microcrystalline silicon (μc-Si:H) solar cells of up to 9.3% (V_oc: 0.501 V, J_sc: 27.4 mA/cm², FF: 0.68) using the n-μc-SiO_x back reflector.