高性能聚合物光伏材料的设计与应用

高性能聚合物光伏材料对于推动聚合物太阳能电池领域的发展具有十分重要的作用.随着研究的深入,聚合物光伏材料从早期的聚噻吩体系逐步发展到具有推拉电子作用的给体-受体(D-A)交替共聚物,其相应的器件光伏效率也从最初的1%左右提升到如今超过11%.近十年来,种类繁多的给受体单元被开发并应用于聚合物材料的构建中,其中基于苯并二噻吩(BDT)单元的聚合物材料因为具有良好的光伏性能,得到了十分广泛的应用.近年来,非富勒烯受体的迅速发展给聚合物太阳能电池的研究注入了新的活力,BDT类聚合物在基于非富勒烯受体的聚合物太阳能电池中也展现出重要的作用,已经获得了超过11%的光电转化效率.本文简要介绍了我们在高性能聚合物光伏材料的设计与应用中的相关工作,主要分为聚噻吩和苯并二噻吩材料的设计与应用、活性层形貌调控以及非富勒烯聚合物太阳能电池的相关研究.     

Anode Engineering of Highly Efficient Polymer Solar Cells Using Treated ITO

ITO substrates were treated with organic solvent cleaning(OSC), SC1 treatment[V(NH₄OH):V(H₂O₂): V(H₂O)=1:1:5], O₂ plasma and UV ozone, respectively. Combined investigations of atom force microscopy(AFM), water contact angle measurements, ultraviolet photoemission spectroscopy(UPS) and X-ray photoemission spectroscopy(XPS) demonstrated that UV ozone treatment could give rise to the smoothest surface, the most hydrophilic property and the highest work function(WF) of ITO due to the removal of hydrophobic C-O impurity from the ITO surface and the enrichments of more oxygen on the ITO surface. When PEDOT:PSS film[(poly(3,4-ethylenedioxy- thiophene):poly(styrene sulfonate)] was deposited on the ITO substrates treated with UV ozone, it showed a lower root-mean- square roughness in AFM images, a higher transmission in UV-Vis transmission spectra and a higher WF in UPS spectra than the PEDOT:PSS films deposited on the ITO substrates treated by other three methods. As a result, the power conversion efficiency of polymer solar cells(PSCs) based on PTB7:PC₇₁BM as an active layer and ITO treated by UV ozone as an anode can reach 8.48% because of the simultaneously improved short circuit current, open circuit voltage and fill factor compared to the PSCs with ITO treated with other three methods.     

Polymer Electron Acceptors Based on Fluorinated Isoindigo Unit for Polymer Solar Cells

Most of efficient polymer electron acceptors for polymer solar cells (PSCs) are based on naphthalene diimide or perylene diimide as the electron deficient building block. In this paper, for the first time, we report polymer electron acceptors based on fluorinated isoindigo (F‐IID) as the electron deficient building block. We synthesized two polymer electron acceptors consisting of alternating F‐IID unit and thiophene/selenophen unit. They show low‐lying LUMO/HOMO energy levels of –3.69/–5.69 eV, high electron mobilities of 1.31×10^–5 cm²·V^–1·s^–1 and broad absorption spectra with the optical bandgap of 1.61 eV. PSC devices using the two F‐IID‐based polymers as polymer electron acceptors show encouraging power conversion efficiencies (PCEs) of up to 1.50% with an open‐circuit voltage (V_OC) of 0.97 V, a short‐circuit current density (J_SC) of 2.91 mA·cm^–2, and a fill factor (FF) of 53.2%. This work suggests a new kind of polymer electron acceptors based on F‐IID unit.     

Benzodithiophene-Fused Perylene Bisimides as Electron Acceptors for Non-Fullerene Organic Solar Cells with High Open-Circuit Voltage

Tandem-junction organic solar cells require solar cells with visible light photo-response as front cells, in which an open-circuit voltage (V_oc) above 1.0 V is highly demanded. In this work, we are able to develop electron acceptors to fabricate non-fullerene organic solar cells (NFOSCs) with a very high V_oc of 1.14 V. This was realized by designing perylene bisimide (PBI)-based conjugated materials fused with benzodithiophene, in which Cl and S atom were introduced into the molecules in order to lower the frontier energy levels. The fused structures can reduce the aggregation of PBI unit and meanwhile maintain a good charge transport property. The new electron acceptors were applied into NFOSCs by using Cl and S substituted conjugated polymers as electron donor, in which an initial power conversion efficiency of 6.63 % and a high V_oc of 1.14 V could be obtained. The results demonstrate that the molecular design by incorporating Cl and S atom into electron acceptors has great potential to realize high performance NFOSCs.     

Benzotriazole-Bridged Sensitizers Containing a Furan Moiety for Dye-Sensitized Solar Cells with High Open-Circuit Voltage Performance

Two new benzotriazole-bridged sensitizers are designed and synthesized ( BTA-I and BTA-II ) containing a furan moiety for dye-sensitized solar cells (DSSCs). Two corresponding dyes ( BTA-III and BTA-IV ) with a thiophene spacer were also synthesized for comparison. All of these dyes performed as sensitizers for DSSCs, and the photovoltaic performance data of these benzotriazole-bridged dyes showed a high open-circuit voltage (V_oc: 804–834 mV). Among the four dyes, DSSCs based on BTA-II , with a furan moiety and branched alkyl chain, showed the highest V_oc (834 mV), a photocurrent density (J_sc) of 12.64 mA cm⁻², and a fill factor (FF) of 0.64, corresponding to an overall conversion efficiency (η) of 6.72 %. Most importantly, long-term stability of the BTA-I , BTA-II , BTA-III , BTA-IV -based DSSCs with ionic-liquid electrolytes under 1000 h light-soaking was demonstrated, and BTA-II exhibited better photovoltaic performance of up to 5.06 % power conversion efficiency.     

高效率有机太阳能电池的界面工程研究

有机太阳能电池(OSC)为典型的三明治结构,是以共轭类有机化合物为活性层材料将太阳光转换为电能,通过两个电极输出电流。这些有机物具有来源广、质量轻和可再生等优点,使得有机太阳能电池在清洁新能源领域备受关注。当前研究的焦点仍然是提高电池的光电转换效率,主要通过改善活性层材料、优化器件结构和界面修饰等途径。本文重点介绍了作者课题组在界面工程方面所做的代表性工作,通过引入含磺酸基团或羧酸基团的超支化结构的聚合物阴极修饰层材料,获得了高效的OSCs;合成了新颖的非共轭有机小分子电解质修饰层,制备了高达10.02%效率的单结正型OSCs。此外,还研究了简单的极性溶剂处理,如甲醇能够优化活性层形貌,提高电池器件的性能。     

Unaxisymmetric Non-Fused Electron Acceptors for Efficient Polymer Solar Cells

Chinese Journal of Polymer Science - To develop photovoltaics embracing the both features of high performance and low cost has drawn attentions of researchers, yet representing the significant...     

Polymer Acceptor Based on B←N Units with Enhanced Electron Mobility for Efficient All‐Polymer Solar Cells

We demonstrate that polymer electron acceptors with excellent all‐polymer solar‐cell (all‐PSC) device performance can be developed from polymer electron donors by using B←N units. By alleviating the steric hindrance effect of the bulky pendant moieties on the conjugated polymers that contain B←N units, the π–π stacking distance of polymer backbones is decreased and the electron mobility is consequently enhanced by nearly two orders of magnitude. As a result, the power conversion efficiency of all‐PSCs with the polymer acting as the electron acceptor is greatly improved from 0.12 % to 5.04 %. This PCE value is comparable to that of the best all‐PSCs with state‐of‐the‐art polymer acceptors.     

Highly Fluorinated and Crosslinkable Dendritic Polymer for Photonic Applications

Summary: A novel crosslinkable dendritic polymer has been synthesized by the thermal polymerization of peripheral aryl trifluorovinyl ether moieties of a highly fluorinated dendrimer. The resulting perfluorocyclobutane(PFCB)‐containing dendritic polymer exhibited excellent processability, low optical loss (0.36 dB · cm⁻¹ at 1 310 nm with 1% dye doping), high thermal stability, and good solvent resistance for waveguide‐based photonic applications.

Structure of the crosslinkable fluorinated dendrimer synthesized.     

Enhanced Hole Transport in Ternary Blend Polymer Solar Cells

Recently, ternary blend polymer solar cells have attracted great attention to improve a short-circuit current density (J_SC) effectively, because complementary absorption bands can harvest the solar light over a wide wavelength range from visible to near-IR region. Interestingly, some ternary blend solar cells have shown improvements not only in J_SC but also in fill factor (FF). Previously, we also reported that a ternary blend solar cell based on a low-bandgap polymer (PTB7-Th), a wide-bandgap polymer (PDCBT), and a fullerene derivative (PCBM) exhibited a higher FF than their binary analogues. Herein, we study charge transport in PTB7-Th/PDCBT/PCBM ternary blend films to address the origin of the improvement in FF. We found that hole polarons are located in PTB7-Th domains and their mobility is enhanced in the ternary blend film.     

Highly Flexible and Efficient All‐Polymer Solar Cells with High‐Viscosity Processing Polymer Additive toward Potential of Stretchable Devices

Considering the potential applications of all‐polymer solar cells (all‐PSCs) as wearable power generators, there is an urgent need to develop photoactive layers that possess intrinsic mechanical endurance, while maintaining a high power‐conversion efficiency (PCE).Herein a strategy is demonstrated to simultaneously control the intercalation behavior and nanocrystallite size in the polymer–polymer blend by using a newly developed, high‐viscosity polymeric additive, poly(dimethylsiloxane‐co‐methyl phenethylsiloxane) (PDPS), into the TQ‐F:N2200 all‐PSC matrix. A mechanically robust 10wt% PDPS blend film with a great toughness was obtained. Our results provide a feasible route for producing high‐performance ductile all‐PSCs, which can potentially be used to realize stretchable all‐PSCs as a linchpin of next‐generation electronics.     

A Non-Conjugated Polymer Acceptor for Efficient and Thermally Stable All-Polymer Solar Cells

A non-conjugated polymer acceptor PF1-TS4 was firstly synthesized by embedding a thioalkyl segment in the mainchain, which shows excellent photophysical properties on par with a fully conjugated polymer, with a low optical band gap of 1.58 eV and a high absorption coefficient >10⁵ cm⁻¹, a high LUMO level of −3.89 eV, and suitable crystallinity. Matched with the polymer donor PM6, the PF1-TS4-based all-PSC achieved a power conversion efficiency (PCE) of 8.63 %, which is ≈45 % higher than that of a device based on the small molecule acceptor counterpart IDIC16. Moreover, the PF1-TS4-based all-PSC has good thermal stability with ≈70 % of its initial PCE retained after being stored at 85 °C for 180 h, while the IDIC16-based device only retained ≈50 % of its initial PCE when stored at 85 °C for only 18 h. Our work provides a new strategy to develop efficient polymer acceptor materials by linkage of conjugated units with non-conjugated thioalkyl segments.     

新型梳状共聚物在准固态染料敏化太阳能电池中的应用及其对电子复合的影响

合成了乙烯基咪唑碘盐(VImI)和聚乙二醇单甲醚甲基丙烯酸酯(PEGMA)的梳状共聚物.利用VImI/PEGMA共聚物制备了准固态聚合物电解质.通过光电流密度-电压(J-V)曲线和电导率测定以及电化学阻抗分析,探讨了基于此电解质的染料敏化太阳能电池的电荷传输与界面电子转移机制.结果表明,VImI/PEGMA共聚物可以有效抑制TiO2/电解质界面电子复合并提高TiO2导带能级,敏化电池的光伏性能并不完全取决于电解质的电导率.通过考察共聚物中VImI与PEGMA单元的摩尔比与开路电压的关系,发现共聚物对电子复合的抑制作用主要源于VImI链段.此外,开路电压衰减(OCVD)和瞬态光电流测试结果说明,共聚物能够提高TiO2薄膜的电子寿命,而且对陷阱电子能级的分布具有调节作用.当共聚物在电解质中的质量分数为50%,VImI与PEGMA的摩尔比为5.0时,准固态染料敏化太阳能电池于100mW·cm-2光强下获得了4.10%的光电转换效率.     

苝二酰亚胺:有机膦盐基双组份共混电子传输层及其开路电压接近1.0 V的非富勒烯聚合物太阳电池

The fabrication of high-efficiency organic solar cells requires a cathode interlayer (CIF) having multiple properties such as forming an ohmic contact with the active layer, high electron conductivity, low-density traps, and hole blocking. These roles can be more completely fulfilled by using a suitable binary blended CIF rather than a single molecule based CIF. In this article, we present the roles by using binary blended PDINO (amino N-oxide perylene diimide) and QPhPBr (tetraphenylphosphonium bromide) as the CIF to fabricate fullerene-free polymer solar cells (PSCs) with PBDB-T:IDTBR, a new donor: acceptor combination, as the active layer. The high-lying lowest unoccupied molecular orbital of the acceptor and the low-lying highest occupied molecular orbital (HOMO) of the polymer with small driving force (the donor-acceptor HOMO-HOMO energy offset, ∆HOMO) for the hole transfer, both result in a high open circuit voltage (V_oc). Moreover, our strategy to insert a dual mixed solution of CIF over the blended active layer better facilitates the role, which significantly improves charge extraction and collection, leading to the high V_oc, short-circuit current density (J_sc), and fill factor (FF) observed in comparison to a single CIF material. It was observed that the power conversion efficiency (PCE) increases to 8.27%, with a high V_oc of 1.0 V, using a binary mixture of CBL. Such tremendous improvements in V_oc using well known polymer donors have not been reported till date in binary solar cell systems. This idea demonstrates that the minimum energy loss because of the small ∆HOMO of the D-A combination and the use of a dual mixed layer of CBL together present the future prospects of non-fullerene photovoltaic devices for researchers.     

Planarized Polymer Acceptor Featuring High Electron Mobility for Efficient All-Polymer Solar Cells

Chinese Journal of Polymer Science - Significant progress has been achieved for all-polymer solar cells (APSCs) in the last few years by the use of polymerized small molecular acceptors (PSMAs)....     

A Multifunctional Polymer as an Interfacial Layer for Efficient and Stable Perovskite Solar Cells

Metal-cation defects and halogen-anion defects in perovskite films are critical to the efficiency and stability of perovskite solar cells (PSCs). In this work, a random polymer, poly(methyl methacrylate-co-acrylamide) (PMMA-AM), was synthesized to serve as an interfacial passivation layer for synergistically passivating the under-coordinated Pb²⁺ and anchor the I^- of the [PbI₆]⁴⁻ octahedron. Additionally, the interfacial PMMA-AM passivation layer cannot be destroyed during the hole transport layer deposition because of its low solubility in chlorobenzene. This passivation leads to an enhancement in the open-circuit voltage from 1.12 to 1.22 V and improved stability in solar cell devices, with the device maintaining 95 % of the initial power conversion efficiency (PCE) over 1000 h of maximum power point tracking. Additionally, a large-area solar cell module was fabricated using this approach, achieving a PCE of 20.64 %.     

Perovskite Films Regulation via Hydrogen-Bonded Polymer Network for Efficient and Stable Perovskite Solar Cells

Perovskite solar cells (PSCs) are considered as a promising photovoltaic technology due to their high efficiency and low cost. However, their long-term stability, mechanical durability, and environmental risks are still unable to meet practical needs. To overcome these issues, we designed a multifunctional elastomer with abundant hydrogen bonds and carbonyl groups. The chemical bonding between polymer and perovskite could increase the growth activation energy of perovskite film and promote the preferential growth of high-quality perovskite film. Owing to the low defect density and gradient energy-level alignment, the corresponding device exhibited a champion efficiency of 23.10 %. Furthermore, due to the formation of the hydrogen-bonded polymer network in the perovskite film, the target devices demonstrated excellent air stability and enhanced flexibility for the flexible PSCs. More importantly, the polymer network could coordinate with Pb²⁺ ions, immobilizing lead atoms to reduce their release into the environment. This strategy paves the way for the industrialization of high-performance flexible PSCs.     

A Multifluorination Strategy Toward Wide Bandgap Polymers for Highly Efficient Organic Solar Cells

Creating new electron-deficient unit is highly demanded to develop high-performance polymer donors for non-fullerene organic solar cells (OSCs). Herein, we reported a multifluorinated unit 4,5,6,7-tetrafluoronaphtho[2,1-b : 3,4-b′]dithio-phene (FNT) and its polymers PFNT-F and PFNT-Cl. The advantages of multifluorination: (1) it enables the polymers to exhibit low-lying HOMO (≈−5.5 eV) and wide band gap (≈2.0 eV); (2) the short interactions (F⋅⋅⋅H, F⋅⋅⋅F) endow the polymers with properties of high film crystallinity and efficient hole transport; (3) well miscibility with NFAs that leads to a more well-defined nanofibrous morphology and face-on orientation in the blend films. Therefore, the PFNT-F/Cl : N3 based OSCs exhibit impressive FF values of 0.80, and remarkable PCEs of 17.53 % and 18.10 %, which make them ranked the best donor materials in OSCs. This work offers new insights into the rational design of high-performance polymers by multifluorination strategy.     

Inorganic Pb‐Free Perovskite Light Absorbers for Efficient Perovskite Solar Cells with Enhanced Performance

Recently, enormous efforts have been made to develop the efficient, lead (Pb) free and stable perovskite solar cells (PSCs). In this regards, various strategies were applied and the optoelectronic properties of various Pb free perovskites such as (CH₃NH₃)₃Sb₂I₉, (CH₃NH₃)₃Bi₂I₉, Cs₃Sb₂I₉, Cs₃Bi₂I₉, CH₃NH₃SnI₃ and CH₃NH₃GeI₃ etc have been investigated. However, the photovoltaic performance of the developed PSCs was still low and presence of organic moieties in common hole‐transport materials (HTMs) shows poor stability against moisture and heat. Herein, we have investigated the optoelectronic properties of all inorganic Pb free perovskites (Cs₃Sb₂I₉=1 and Cs₃Bi₂I₉=2) and employed novel strategies (dissolution‐recrystallization) to prepare the efficient Pb free PSCs. The band gaps of the 1 and 2 were found to be 2.2 eV and 2.0 eV, respectively. The developed PSCs with 1 and 2 exhibited the power conversion efficiency of 0.68% and 1.087%, respectively.