ZnO电子传输层对于反型结构聚合物太阳电池光浴效应的影响

采用金属氧化物电子传输层(ETL)的聚合物光伏器件在制备完成之初通常性能表现低下, J-V曲线呈异常“S”形. 当器件受白光持续照射后, 该不良状况会逐渐好转, 此过程称为光浴(light-soaking). 光浴现象普遍被认为是ETL界面问题所致. 从器件结构着手, 研究了ZnO 纳米颗粒ETL相邻的两个界面在光浴问题上的作用. 制备了功能层相同的(电极除外)正型、反型器件及复合ETL结构器件, 发现光浴现象仅出现于包含ZnO/ITO界面的反型器件中, 证明该界面是导致光浴现象的主要原因. 分析认为: ZnO颗粒表面O₂吸附形成的电子陷阱增加了ITO/ZnO势垒厚度, 使得光生电子无法逾越而成为空间电荷积累, 从而导致器件初始性能不佳. 器件经光照后, ETL内部受激而生的空穴电子对填补了ZnO缺陷, 提升了ETL的电荷选择性并减小了界面势垒厚度, 被束缚的光生电子得以隧穿至ITO电极, 反型器件性能最终得以改善.     

Mg-doped ZnO layer to enhance electron transporting for PbS quantum dot solar cells

In this work, the effect of Mg doping on the performance of PbS quantum dot (QD) solar cells (QDSCs) is investigated. To elucidate that, PbS QDSCs with pristine ZnO and Mg-doped ZnO (ZMO) as electron transporting layers (ETLs) are fabricated, respectively. The current density-voltage (J-V) measurements are performed. The results show that the cell efficiency of the device with ZMO as an ETL is 9.46%, which increases about 75% compared to that of the pristine ZnO based device (5.41%). Enhanced short current density (J_sc) and fill factor (FF) are observed. It is demonstrated that Mg doping could passivate the surface defects and suppress the carrier recombination in ZnO ETL, thus resulting in larger bandgap and higher Fermi level (E_F). The strategy of Mg-doped ZnO ETL provides a promising way for pushing solar cell performance to a high level.     

Highly crystalline bilayer electron transport layer for efficient conjugated polymer solar cells

Solution processed solar cells are a promising renewable energy technology due to the low fabrication costs. The most commonly used electron transport layer for solution processed organic solar cells is ZnO. However, sol-gel derived ZnO is amorphous, which limits interfacial charge transport. In this study, we demonstrate a ZnO bilayer, composed of a nanoparticle ZnO and sol-gel derived ZnO layer, as the electron transport layer in polymer solar cells incorporating the novel polymer poly [(5,6-difluoro-2,1,3-benzothiadiazol-4,7-diyl)-alt-(3,3‴-di (2-octyldodecyl)-2,2′; 5′,2″; 5″,2‴-quaterthiophen-5,5‴-diyl)] (PffBT4T-2OD). Compared with the single layer sol-gel ZnO, the bilayer displayed enhanced crystallinity. Consequently, the interfacial transport from the active layer was improved, as evidenced by dark J-V and PL spectroscopy measurements. Solar cells incorporating this bilayer ZnO layer achieved PCE values exceeding 10%, a relative improvement of 25% compared to the sol-gel ZnO devices.     

Triaxial strain effect on the electron transport performance and absorption spectrum of ZnO

The effect of triaxial strain on the electron transport performance and absorption spectrum of ZnO has been rarely reported. In this paper, the generalized gradient approximation plane wave ultrasoft pseudopotential + U method based on the spin density functional theory is adopted to solve this problem. The first-principle method is utilized to study the triaxial strain on the electron transport performance and absorption spectrum of ZnO. Results show that the binding energy of Zn₃₆O₃₆ is 2.14 eV when the system is unstrained and relatively stable. The formation energy of the Zn₃₆O₃₆ system increases with the increase in tensile or compressive strain, and the system stability decreases. The formation energy of the O-vacancy system is smaller compared with the same orders of magnitude of tensile or compressive strain. The formation energy of O-vacancy system is smaller, and the structure is stable when the system is tensile strain. Specifically, the absorption spectrum of the Zn₃₆O₃₅ system has the optimal redshift and intensity when the tensile strain is 5%. The electron mobility of the Zn₃₆O₃₆ system along the y direction (G → F) is relatively large when the compressive strain is −5%, the band gap of the system is wide, and the blueshift of the absorption spectral distribution is obvious. This work has a certain theoretical guidance for the design and preparation of novel ultraviolet light detectors or improvement of the electron transmission performance.     

ITO-free inverted organic solar cells fabricated with transparent and low resistance ZnO/Ag/ZnO multilayer electrode

Inverted organic solar cells (OSCs) based on poly (3-hexylthiophene) (P3HT):[6,6]-phenyl-C61 butyric acid methyl ester (PCBM) bulk heterojunctions (BHJ) were fabricated with optimized ZnO/Ag/ZnO multilayer and conventional indium–tin oxide (ITO) cathode electrodes and their performance was compared. The ZnO/Ag/ZnO multilayer films showed sheet resistances in the range 3.6–3.9 Ω/sq, while ITO exhibited 14.2 Ω/sq. On the one hand, the carrier concentration gradually decreased from 1.74 × 10²² to 4.33 × 10²¹ cm⁻³ as the ZnO thickness increased from 8 to 80 nm, respectively. The transmittance of the ZnO(40 nm)/Ag(19 nm)/ZnO(40 nm) films was ∼95% at 550 nm, which is comparable to that of ITO (∼96%). The multilayer films were smooth with a root mean square (RMS) roughness of 0.81 nm. OSCs fabricated with the ZnO(40 nm)/Ag(19 nm)/ZnO(40 nm) film showed a power conversion efficiency (2.63%) comparable to that of OSCs with a conventional ITO cathode (2.71%).     

A simulation study on p-doping level of polymer host material in P3HT:PCBM bulk heterojunction solar cells

In this study,we investigate the influence of doping on the charge transfer and device characteristics parameters in the bulk heterojunction solar cells based on poly(3-hexylthiophene)(P3HT) and a methanofuUerene derivative(PCBM).Organic semiconductors are also known to be not pure and they have defects and impurities,some of them are being charged and act as p-type or n-type dopants.Calculations of the solar cell characteristics parameters versus the p-doping level have been done at three different n-dopings(N_d) that consist of 5 × 10~(17) cm~(-3),10~(18) cm~(-3),and 5 × 10~(18) cm~(-3).We perform the analysis of the doping concentration through the drift-diffusion model,and calculate the current and voltage doping dependency.We find that at three different n-dopant levels,optimum p-type doping is about N_p = 6 × 10~(18) cm~(-3).Simulation results have shown that by increasing doping level,V_(oc) monotonically increases by doping.Cell efficiency reaches its maximum at somewhat higher doping as FF has its peak at N_p = 3 × 10~(18) cm~(-3).Moreover,this paper demonstrates that the optimum value for the p-doping is about N_p = 6 × 10~(18) cm~(-3) and optimum value for n-dopant is N_d = 10~(18) cm~(-3),respectively.The simulated results confirm that doping considerably affects the performance of organic solar cells.     

Highly efficient inverted polymer solar cells using aqueous ammonia processed ZnO as an electron selective layer

The authors demonstrate a simple method to deposit solution-processable ZnO thin film by directly dissolving the ZnO powder into aqueous ammonia. ZnO film casting from its aqueous ammonia solution (a-ZnO) is used successfully as an electron selective layer in poly(3-hexylthiophene) and indene-C₆₀ bisadduct (IC₆₀BA) based heterojunction solar cells with improved power conversion efficiency (PCE) compared with that using conventional sol–gel based ZnO (c-ZnO). The improved PCE is mainly attributed to an increase of short-circuit current density owing to the better transmittance of a-ZnO than that of c-ZnO in the absorption range of IC₆₀BA, and efficient electron extraction at cathode. In addition, no additional by-products originated from the organic solvents are introduced as like in sol–gel based ZnO films.     

ZnO nanorods on undoped and indium-doped ZnO thin films as a TCO layer on nonconductive glass for dye-sensitized solar cells

We present the growth of ZnO nanostructures on indium-doped ZnO film on a non-conductive glass substrate. The indium-doped ZnO film was used as the transparent conductive layer replaces the ITO layer. Various indium doping concentrations can change the electrical properties of ZnO film. The reduced electrical resistivity was investigated from 16.60 × 10⁻² to 10 × 10⁻² Ω cm. after doping with the optimal concentration of 2 wt% indium. It is found that the characteristic of ZnO nanostructures was strongly affected with indium doping concentration in ZnO films. The overall structural characteristics of ZnO ranged from 100–500 nm in size and 7–10 μm in length and the branch-like structures can be revealed from the 2 wt% indium-doped ZnO film. The room-temperature photoluminescence spectra show a sharp ultraviolet band of 353 nm, indicated to the ZnO nanorods structure. The branch-like structures on the 2 wt% indium-doped film can be yielded the photovoltaic properties with a short-circuit current density of 3.96 mA/cm², an open-circuit voltage of 0.72 V, a fill factor of 20% and an overall power conversion efficiency of 0.56% under irradiance of 100 mW/cm² (AM 1.5 G).     

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.     

Light absorption modeling of ordered bulk heterojunction organic solar cells

Ordered bulk heterojunction organic solar cells are devices that combine the advantages of the planar bilayer and the bulk heterojunction architectures. They offer uninterrupted pathways to electrodes for effective charge collection and an extended Donor–Acceptor interface for efficient exciton dissociation. Additionally, this interface can also be a potential approach to increase photon absorption by light trapping. Light absorption and charge carrier generation of organic nanostructures are studied by means of finite-element modeling for a wide range of structuring widths, periods and heights for poly(3-hexylthiophene):1-(3-methoxycarbonyl)-propyl-1-phenyl-(6,6)C₆₁ (P3HT:PCBM) structures. Results show an increase in light absorption at certain wavelengths in the P3HT region with respect to an equivalent planar bilayer model. This increase can be attributed to two phenomena: for the smallest periods the structures behaves like an effective medium, while for periods of the order of magnitude of the incident light wavelength there is light trapping. The maximum increase in absorption was achieved for a 250 nm-width and 500 nm periodicity structure with a height of 40 nm. Exciton diffusion has also been studied to evaluate the effective amount of absorbed light contributing to photocurrent. In this case, best results correspond to the smallest sizes (1.25–12.5 nm-width) for all the considered heights, achieving an increment in the photocurrent up to more than a factor 6 if compared with that of the reference planar bilayer device. This study can be used to optimize our devices, which are achieved via nanoporous anodic alumina templates.     

Fabrication and characterization of ZnTPP:PCBM bulk heterojunction (BHJ) solar cells

Bulk heterojunction (BHJ) solar cells were fabricated based on blended films of a porphyrin derivative 5,10,15,20-Tetraphenyl-21H,23H-porphine zinc (ZnTPP) and a fullerene derivative [6,6]-phenyl-C₆₁ butyric acid methyl ester (PCBM) as the active layer. The ZnTTP:PCBM BHJ solar cells were fabricated by spin-casting of the blended layer. The weight ratios of ZnTPP and PCBM were varied from 1:1 to 0:10. The electronic and optical properties of each cell were investigated. Optical density (OD) of the blended film for each cell was extracted from its reflection and transmission curves. OD and average absorption coefficients of the active materials were used to determine film thicknesses. Absorption spectra of each component material were compared with the spectra of the blended films. Current density–Voltage (J–V) characteristics were recorded under dark as well as under the illumination of AM 1.5G (1 sun) solar spectrum. The BHJ solar cell with ZnTPP:PCBM ratio of 1:9 showed the best performance . The values of RR, V_OC , J_SC , FF and η for these ratios were 106.3, 0.4 V, 1.316 mA/cm², 0.4 and 0.21%, respectively. The cross-section of this device using SEM was also examined.     

双电子传输层结构硫硒化锑太阳电池的界面特性优化

硫硒化锑薄膜太阳电池因其制备方法简单、原材料丰富无毒、光电性质稳定等优点,成为了光伏领域的研究热点.经过近几年的发展,硫硒化锑太阳电池的光电转换效率已经突破10%,极具发展潜力.本文针对硫硒化锑太阳电池中n/i界面引起的载流子复合进行了深入研究.发现硫硒化锑太阳电池的界面特性会受到界面电子迁移能力和能带结构两方面的影响.界面电子迁移率的提高能使电子更有效地传输至电子传输层,实现器件短路电流密度和填充因子的有效提升.在此基础上,引入ZnO/Zn_1-xMg_xO双电子传输层结构能够进一步优化硫硒化锑太阳电池性能.其中,Zn_1-xMg_xO能级位置的改变可以同时调节界面和吸光层的能级分布,在Zn_1-xMg_xO导带能级为-4.2 eV,对应Mg含量为20%时,抑制载流子复合的效果最为明显,硫硒化锑太阳电池也获得了最佳的器件性能.在去除缺陷态的理想情况下,双电子传输层结构硫硒化锑太阳电池在600 nm厚时获得了20.77%的理论光电转换效率,该研究结果为硫硒化锑太阳电池...     

The effect of various solvent additives on the power conversion efficiency of polymer-polymer solar cells

We investigated the effect of three different additives (1-chloronaphthalene, 1,8-diiodooctane, diphenylether) on the performance of polymer-polymer solar cells based on a BHJ blend consisting of poly[4,8-bis(5-(2-ethylhexyl)thiophen-2-yl)benzo[1,2-b:4,5-b′]dithiophene-alt-3-fluorothieno[3,4-b]thiophene-2-carboxylate] (PTB7-Th) as a donor and poly[[N,N′-bis(2-octyldodecyl)-naphthalene-1,4,5,8-bis(dicarboximide)-2,6-diyl]-alt-5,5′-(2,2′-bithiophene)] (P(NDI2OD-T2)) as an acceptor. A direct comparison of the efficiency of the solar cells with and without additive indicated that the device using the additive exhibited slightly improved performance. However, the efficiency enhancement was not significant. The optimal ratio of additive differed depending on the properties of the additive. In addition, the performances of polymer-polymer solar cells were not significantly dependent on the type of additive. Identifying the optimal fabrication condition was critical for achieving the highest performance. It is known that the general role of an additive in polymer solar cells based on a BHJ active layer was to induce good phase separation between the donor and acceptor by morphology modification. However, grazing-incidence wide-angle X-ray scattering results showed that no significant morphology change in polymer-polymer active layer was caused by the additive. Rather, our modulated impedance spectroscopy study showed that the performance enhancement in polymer-polymer solar cells with additive was because of improved recombination properties rather than improvements in crystalline morphology.     

Inverted organic solar cells with solvothermal synthesized vanadium-doped TiO_2 thin films as efficient electron transport layer

We investigated the effects of using different thicknesses of pure and vanadium-doped thin films of TiO_2 as the electron transport layer in the inverted configuration of organic photovoltaic cells based on poly(3-hexylthiophene) P3HT:[6-6] phenyl-(6) butyric acid methyl ester(PCBM). 1% vanadium-doped TiO_2nanoparticles were synthesized via the solvothermal method. Crystalline structure, morphology, and optical properties of pure and vanadium-doped TiO_2 thin films were studied by different techniques such as x-ray diffraction, scanning electron microscopy, transmittance electron microscopy, and UV–visible transmission spectrum. The doctor blade method which is compatible with roll-2-roll printing was used for deposition of pure and vanadium-doped TiO_2 thin films with thicknesses of 30 nm and 60 nm. The final results revealed that the best thickness of TiO_2 thin films for our fabricated cells was 30 nm. The cell with vanadium-doped TiO_2 thin film showed slightly higher power conversion efficiency and great J_(sc) of 10.7 mA/cm~2 compared with its pure counterpart. In the cells using 60 nm pure and vanadium-doped TiO_2 layers, the cell using the doped layer showed much higher efficiency. It is remarkable that the external quantum efficiency of vanadium-doped TiO_2 thin film was better in all wavelengths.     

Theoretical design of azaacene-based non-fullerene electron transport material used in inverted perovskite solar cells

ABSTRACT

Inverted perovskite solar cells (PSCs) have attracted much attention due to their low-temperature and solution-based process. Electron transport layers are important components in inverted PSCs. Non-fullerene n-type organic small molecules seem to be more attractive as electron transport layers, because their structures are easy to be synthesised and modified. In this paper, density functional theory and semi-classical Marcus electron transfer theory were used to explore the electron transport properties in three azaacene derivatives, including one experimentally reported molecule, 1,4,9,16-tetrakis((triisopropylsilyl)ethynyl)quinoxalino[2^?,3^?:4^″,5^″]cyclopenta[1^″,2^″,3^″:5^′,6^′]acenaphtho[1^′,2^′:5,6]pyrazino[2,3-b]phenazine (1), and two theoretically designed molecules (2 and 3). Compound 2 is formed by substituting i-Pr groups in compound 1 with H atoms, which is designed to evaluate the effect of i-Pr groups on the electron transport properties. Compound 3 is designed by adding one more benzopyrazine group to the conjugation structure of compound 1. It shows that i-Pr group can increase HOMO and LUMO energy levels and improve solubility in organic solvent and hydrophobicity. Enlarging conjugation can not only decrease LUMO energy level and electron reorganisation energy, but also can increase solubility and electron mobility. So our designed compound 3 is expected to be a potential electron transport material in inverted PSCs.     

MoO3/Ag/AI/ZnO intermediate layer for inverted tandem polymer solar cells

We report an MoO3/Ag/Al/ZnO intermediate layer connecting two identical bulk heterojunction subcells with a poly（3-hexylthiophene） and [6,6]-phenyl-C61-butyric acid methyl ester （P3HT and PCBM） active layer for inverted tan- dem polymer solar cells. The highly transparent intermediate layer with an optimized thickness realizes an Ohmic contact between the two subcells for effective charge extraction and recombination. A maximum power conversion efficiency of 3.76% is obtained for the tandem cell under 100 mW/cm2 illumination, which is larger than that of a single cell （3.15%）. The open-circuit voltage of the tandem cell （1.18 V） approaches double that of the single cell （0.61 V）.     

MoO_3/Ag/Al/ZnO intermediate layer for inverted tandem polymer solar cells

We report an MoO3/Ag/Al/ZnO intermediate layer connecting two identical bulk heterojunction subcells with a poly(3-hexylthiophene) and [6,6]-phenyl-C61-butyric acid methyl ester(P3HT and PCBM) active layer for inverted tandem polymer solar cells. The highly transparent intermediate layer with an optimized thickness realizes an Ohmic contact between the two subcells for effective charge extraction and recombination. A maximum power conversion efficiency of 3.76% is obtained for the tandem cell under 100 mW/cm2 illumination, which is larger than that of a single cell(3.15%).The open-circuit voltage of the tandem cell(1.18 V) approaches double that of the single cell(0.61 V).     

Fabrication and characterization of fullerene/porphyrin bulk heterojunction solar cells

Fullerene/porphyrin bulk heterojunction solar cells were fabricated and, the electronic and optical properties were investigated. Effects of exciton-diffusion blocking layer of perylene derivative on the solar cells between active layer and metal layer were also investigated. Optimized structures with the exciton-diffusion blocking layer improved conversion efficiencies. Energy levels of the molecules were calculated and discussed. Nanostructures of the solar cells were investigated by X-ray and electron diffraction, which indicated formation of fullerene/porphyrin mixed crystals. Electronic structures of the molecules were investigated by molecular orbital calculation, and energy levels of the solar cells were discussed.     

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...     

基于聚多巴胺/氧化锌复合阴极缓冲层的倒置聚合物太阳能电池的研究

利用多巴胺氧化自聚合形成聚多巴胺(PDA)与ZnO结合形成PDA/ZnO复合阴极缓冲层,制备了以P3HT:PC_(61)BM为活性层的倒置结构聚合物太阳能电池,通过改变PDA的自聚合时间来分析复合阴极缓冲层对器件性能的影响.实验发现,随着PDA的自聚合时间的增加,聚合物太阳能电池的光电转换效率先增大后减小,当自聚合时间为10 min时,相应器件光伏性能达到最优值,其开路电压V_(OC)为0.66 V,短路电流密度J_(SC)为9.70 mA/cm~2,填充因子FF为68.06%,光电转换效率PCE为4.35%.器件性能改善的原因是由于PDA/ZnO复合阴极缓冲层减小了ZnO与ITO之间的接触电阻,同时PDA中存在大量的氨基有利于倒置太阳能电池阴极对电子的收集.