基于噻吩-苯非对称单元的DPP类聚合物给体材料的合成及光伏性能

为了优化聚合物太阳能电池的光伏性能,设计合成了一种基于噻吩-苯非对称单元的二酮吡咯并[3,4-c]吡咯(DPP)类聚合物给体材料(PDPP-PT).非对称结构的设计使得该聚合物具有较好的分子堆积,有利于器件的制备.该聚合物具有范围在300~900 nm的宽吸收光谱、1.5 eV的窄光学带隙.在器件性能方面,活性层厚度达260 nm时,测得开路电压(Voc)为0.68 V,光电转换效率(PCE)为1.51%.因此,PDPP-PT给体材料在制备厚活性层太阳能电池时具有一定的优势并为聚合物给体材料的分子设计提供了一种新的思路.     

基于噻吩-苯非对称单元的DPP类聚合物给体材料的合成及光伏性能

为了优化聚合物太阳能电池的光伏性能,设计合成了一种基于噻吩-苯非对称单元的二酮吡咯并[3,4-c]吡咯(DPP)类聚合物给体材料(PDPP-PT)。非对称结构的设计使得该聚合物具有较好的分子堆积,有利于器件的制备。该聚合物具有范围在300~900nm的宽吸收光谱、1.5eV的窄光学带隙。在器件性能方面,活性层厚度达260nm时,测得开路电压(Voc)为0.68V,光电转换效率(PCE)为1.51%。因此,PDPP-PT给体材料在制备厚活性层太阳能电池时具有一定的优势并为聚合物给体材料的分子设计提供了一种新的思路。     

新型二吡咯类有机荧光材料的合成及其性能研究

以富电子基团吡咯并[3,2-b]吡咯作为电子给体,在其2,5取代位上修饰不同的电子受体,设计合成了两个D-π-A结构的有机荧光材料2,5-二(4-(苯磺酰基)苯基)-1,4-二(4-叔丁基苯基)吡咯并[3,2-b]吡咯(DPSPP)和2,5-二(5,5-二氧-2-二苯并噻吩基)-1,4-二(4-叔丁基苯基)吡咯并[3,2-b]吡咯(BTPP)。通过热重分析研究了其热稳定性,通过紫外-可见吸收光谱、荧光光谱以及电化学法系统分析了其光致发光性能和结构的关系。通过改变吸电子能力以及共轭程度的大小,实现了发光光谱从蓝光到绿光的系统调节并伴随较高的荧光量子产率达到90%以上,在有机发光领域具有潜在的应用前景。     

新型窄带隙聚合物太阳能电池材料的合成及性能研究

为了寻找更优异的太阳能电池材料,通过stille偶联反应以2,2′-联噻吩作为给体单元,以4,7-二(3-己基噻吩-2-基)-5,6-二氟-[2,1,3]苯并噻二唑作为受体单元,合成了一种新型聚合物。通过引入支链和氟原子提高了聚合物的性质。利用傅里叶变换红外光谱仪和核磁共振氢谱仪表征了聚合物的结构,采用热重差热综合热分析仪表征了聚合物的热稳定性,并通过紫外-可见吸收光谱和循环伏安法研究了其光电性能。结果表明,聚合物的热分解温度为366℃,带隙为2.16eV,理论开路电压为1.02V,在聚合物太阳能电池的制备中可将其作为给体材料。     

基于苯并二噻吩单元的窄带系D—A共聚物太阳能电池材料的合成及器件测试

用Stille聚合法合成了基于4,8-二（2,3-二已基噻吩）苯并[1,2-b：4,5-b’]二噻吩（BDTT）和噻吩并[3,4-c]吡咯-4,6-二酮（TPD）单元的窄带系D-A共聚物PBDTT-LTPD-M,其主链内受体单元的密度增加,具有较低的HOMO能级（-5．50eV）。用于聚合物太阳能电池中,使电池的开路电压（Voc）达到0．87V,器件的短路电流（Jsc）为6．07mA／cm^2,填充因子（FF）50．22％,光电转换效率（PCE）为2．67％。     

从分子结构层面调控共混膜形貌，提升光伏器件性能

正给受体材料间互补的吸收光谱、匹配的分子能级,以及良好的纳米尺寸分离形貌是实现高效聚合物太阳能电池的关键.对光伏材料吸收光谱和分子能级的调控可通过许多简单易行的分子设计策略直观地实现;但由于活性层形貌受到诸多因素的影响,从分子结构层面实现对共混膜形貌的有效调控具有很大的挑战性.最近,苏州大学李永舫院士团队的崔超华副教授等通过聚合物给体材料上的共轭侧链工程,简单有效地实现了对共混膜形貌的优化.他们将烷硫基噻吩取代的BDT单元和烷硫基苯基取代的BDT单元分别与NTDO单元共聚,设计合成了两种聚合物给体材料PBNT-S和PBNP-S.PBNT-S和PBNP-S具有非常相似的吸收光谱和分子能级,说明BDT单元上两种不同的     

有机太阳能电池受体材料的研究进展

有机太阳能电池受体材料是有机光伏领域的研究热点之一。主要介绍了富勒烯衍生物、苝二酰亚胺衍生物、9,9-联亚芴基衍生物、二酮吡咯并吡咯衍生物和聚合物这五类受体材料的结构与特点,并综述了这些受体材料在有机光伏器件中的应用与发展,为今后开发更加高效的有机太阳能电池受体材料提供参考。     

基于苯并二噻吩的非对称型小分子给体材料的合成及其在有机太阳能电池中的应用

以烷氧基和苯基作为一维和二维取代基来构造非对称型的苯并二噻吩(BDT)结构,以三联噻吩作为偶联π桥,以氰基乙酸异辛酯作为封端基团,设计并合成了基于非对称型BDT的小分子DCA3TPBDTOC16和DCA3TFPBDTOC16-m,并首次将该类型的小分子作为活性层给体材料应用到有机太阳能电池器件中。两个小分子均表现出良好的热稳定性,较宽的吸收峰和较为平整的平面构型,最终,小分子DCA3TPBDTOC16表现出0.30%的光电转换效率(PCE),相应的开路电压(VOC)为0.387V,短路电流密度(JSC)为2.126mA/cm2,填充因子(FF)为29.39%,在此基础上,在BDT侧链上的苯环取代基上引入F原子来优化来调控分子能级,最终小分子DCA3TFPBDTOC16-m表现出了1.20%的PCE值,VOC为1.007V,JSC为1.61 mA/cm2,FF为29.34%,其中VOC=1.007V与目前为止基于苯并二噻吩的小分子给体材料所表现出的最高开路电压值相近。这些结果表明,基于非对称型BDT的小分子给体材料在有机太阳能电池应用上具有巨大的潜力。     

含F有机供-受体聚合物给体材料研究进展

有机受供体聚合物薄膜太阳能电池的活性层是由共轭材料构成。其中含氟聚合物材料因氟原子的存在,有着优异的物理化学性质而被应用到有机太阳能电池的功能材料中,其不仅能提高有机太阳能电池的光电转化效率,还能增强电池的稳定性。目前已报道的基于含F聚合物的光伏器件(organic photovoltaic device,OPV)光电转化效率(power conversion efficiency,PCE)最高已达到12%,应用前景巨大。综述了3类受体单元上含F有机聚合物供体材料近几年的研究进展,并简要分析了F原子的个数以及所在区域位置的不同对器件性能的影响。最后对含氟共轭聚合物在有机太阳能电池未来的发展做出了展望。     

新型窄带隙聚合物太阳能电池光伏材料

聚合物太阳能电池中给体材料的能级水平、带隙、光吸收系数、溶解性、成膜性及载流子迁移率是决定器件性能的关键因素.阐述了聚合物太阳能电池中给体材料的最新研究进展,着重介绍了含有苯并双噻吩的窄带隙D-A类型的共聚物,并对一些给体材料的能级水平优化结果做了简单的总结.最后指出了未来聚合物太阳能电池给体材料今后的发展方向.     

Precisely Controlling the Position of Bromine on the End Group Enables Well-Regular Polymer Acceptors for All-Polymer Solar Cells with Efficiencies over 15%

Recent advances in the development of polymerized A–D–A-type small-molecule acceptors (SMAs) have promoted the power conversion efficiency (PCE) of all-polymer solar cells (all-PSCs) over 13%. However, the monomer of an SMA typically consists of a mixture of three isomers due to the regio-isomeric brominated end groups (IC-Br(in) and IC-Br(out)). In this work, the two isomeric end groups are successfully separated, the regioisomeric issue is solved, and three polymer acceptors, named PY-IT, PY-OT, and PY-IOT, are developed, where PY-IOT is a random terpolymer with the same ratio of the two acceptors. Interestingly, from PY-OT, PY-IOT to PY-IT, the absorption edge gradually redshifts and electron mobility progressively increases. Theory calculation indicates that the LUMOs are distributed on the entire molecular backbone of PY-IT, contributing to the enhanced electron transport. Consequently, the PM6:PY-IT system achieves an excellent PCE of 15.05%, significantly higher than those for PY-OT (10.04%) and PY-IOT (12.12%). Morphological and device characterization reveals that the highest PCE for the PY-IT-based device is the fruit of enhanced absorption, more balanced charge transport, and favorable morphology. This work demonstrates that the site of polymerization on SMAs strongly affects device performance, offering insights into the development of efficient polymer acceptors for all-PSCs.     

Dopant-Free Polymer Hole Transport Materials for Highly Stable and Efficient CsPbI3 Perovskite Solar Cells

All-inorganic perovskite CsPbI₃ contains no volatile organic components and is a thermally stable photoactive material for wide-bandgap perovskite solar cells (PSCs); however, CsPbI₃ readily undergoes undesirable phase transitions due to the hygroscopic nature of the ionic dopants used in commonly used hole transport materials. In the current study, the popular donor material PM6 in organic solar cells is used as a hole transport layer (HTL). The benzodithiophene-based backbone-conjugated polymer requires no dopant and leads to a higher power conversion efficiency (PCE) than 2,2′,7,7′-tetrakis[N,N-di(4-methoxyphenyl)amino]-9,9′-spirobifluorene (Spiro-OMeTAD). Moreover, PM6 also shows priorities in hole mobility, hydrophobicity, cascade energy level alignment, and even defect passivation of perovskite films. With PM6 as the dopant-free HTL, the PSCs achieve a champion PCE of 18.27% with a competitive fill factor of 82.8%. Notably, the present PCE is based on the dopant-free HTL in CsPbI₃ PSCs reported thus far. The PSCs with PM6 as the HTL retain over 90% of the initial PCE stored in a glovebox filled with N₂ for 3000 h. In contrast, the PSCs with Spiro-OMeTAD as the HTL maintain ≈80% of the initial PCE under the same conditions.     

Effect of film and device annealing in polymer:polymer solar cells with a LiF nanolayer

We report the effect of thermal annealing on the performance of polymer:polymer solar cells with a lithium fluoride (LiF) nanolayer inserted between active layer and electron-collecting electrode. The active layer was prepared using blend films of regioregular poly(3-hexylthiophene) (P3HT) and poly(9,9-dioctylfluorene-co-benzothiadiazole) (F8BT). Film annealing and device annealing were separately performed at 150 °C for 30 min to understand the influence of the existence of LiF nanolayer during thermal annealing. Results showed that both film and device annealing did considerably improve the power conversion efficiency (PCE) of P3HT:F8BT solar cells though the PCE was higher in the case of device annealing. The surface analysis suggested that the improved device performance by thermal annealing is attributed partly to the formation of planar p-n junction structure in the P3HT:F8BT blend film during thermal annealing.     

New narrow bandgap polymers containing 10-(4-((2-ethylhexyl)oxy)phenyl)-10H-phenothiazine/phenoxazine and 3,6-di(2-thienyl)pyrrolo[3,4-c]pyrrole-1,4-dione)-based units: synthesis and photovoltaic properties

Diketopyrrolopyrrole (DPP) is one of the most used moieties in D–A conjugated polymers for high-performance π-extended conjugated polymer-based organic solar cells. The combination of 1,4-diketo-3,6-dithienylpyrrolo[3,4-c]pyrroles (DTDPPs) and the donor moieties 10-(4-((2-ethylhexyl)oxy)phenyl)-10H-phenothiazine (M₁), 10-(4-((2-ethylhexyl)oxy)phenyl)-10H-phenoxazine (M₂), has not been reported yet. In this report, novel low-bandgap D–A conjugated polymer derivatives including DTDPP, phenothiazine and phenoxazine were successfully synthesized via direct (hetero) arylation polymerization with in the yields of 40.94–60.77%. The obtained D–A conjugated polymers named poly(3,6-Di(2-thienyl)pyrrolo[3,4-c]pyrrole-1,4-dione)-alt-(10-(4-((2-ethylhexyl)oxy) phenyl)-10H-phenothiazine) (P₁) and poly(3,6-Di(2-thienyl)pyrrolo[3,4-c]pyrrole-1,4-dione)-alt-(10-(4-((2-ethylhexyl)oxy) phenyl)-10H-phenoxazine) (P₂) exhibited a wide range of absorption spectrum in visible light region and have a low bandgaps of 1.4–1.5 eV, as well as thermal stabilities, these D–A conjugated polymers are very promising as activated polymeric materials for organic solar cells (OSCs).

     

Thermal effects and plasma damage upon encapsulation of polymer solar cells

A barrier structure consisting of silicon oxide and silicon nitride films was deposited via plasma-enhanced chemical vapor deposition (PECVD) for the encapsulation of polymer solar cells (PSCs). The total concentration of the solution and the ratio of P3HT and PCBM on the performance of polymer solar cells were studied by UV-Vis absorption spectroscopy, atomic force microscopy and photocurrent measurement. Base on these measurements, there is a compromise between light absorption and phase separation with increasing blend concentration. The PSCs were annealed at 80, 100, 120 and 140 °C for 10-60 min to investigate the thermal effects and to estimate the best deposition temperature of the barrier layers. Nevertheless, the devices with the encapsulation of barrier layers had relatively low power conversion efficiencies (PCE) of 0.98% comparing to the devices heated in the PECVD system (1.57%) at the same condition of 80 °C for 45 min due to the plasma damage during the film deposition process. After inserting a 5-nm TiO_x layer between Al/barrier structure and active layer against the plasma damage, the annealed devices presented an average PCE of 2.26% and demonstrated over 50% of their initial value after constant exposure to ambient atmosphere and sunlight for 1500 h.     

A 3-Fluoropyridine Manipulating the Aggregation and Fibril Network of Donor Polymers for Eco-Friendly Solution-Processed Versatile Organic Solar Cells

The development of eco-friendly solvent-processed organic solar cells (OSCs) suitable for industrial-scale production should be now considered the imperative research. Herein, asymmetric 3-fluoropyridine (FPy) unit is used to control the aggregation and fibril network of polymer blends. Notably, terpolymer PM6(FPy = 0.2) incorporating 20% FPy in a well-known donor polymer poly[(2,6-(4,8-bis(5-(2-ethylhexyl-3-fluoro)thiophen-2-yl)-benzo[1,2-b:4,5-b’]dithiophene))-alt-(5,5-(1’,3’-di-2-thienyl-5’,7’-bis(2-ethylhexyl)benzo[1’,2’-c:4’,5’-c’]dithiophene-4,8-dione)] (PM6) can reduce the regioregularity of the polymer backbone and endow them with much-enhanced solubility in eco-friendly solvents. Accordingly, the excellent adaptability for fabricating versatile devices based on PM6(FPy = 0.2) by toluene processing is demonstrated. The resulting OSCs exhibit a high power conversion efficiency (PCE) of 16.1% (17.0% by processed with chloroform) and low batch-to-batch variation. Moreover, by controlling the donor-to-acceptor weight ratio at 0.5:1.0 and 0.25:1.0, semi-transparent OSCs (ST-OSCs) yield significant light utilization efficiencies of 3.61% and 3.67%, respectively. For large-area (1.0 cm²) indoor OSC (I-OSC), a high PCE of 20.6% is achieved with an appropriate energy loss of 0.61 eV under a warm white light-emitting diode (3,000 K) with the illumination of 958 lux. Finally, the long-term stability of the devices is evaluated by investigating their structure–performance–stability relationship. This work provides an effective approach to realizing eco-friendly, efficient, and stable OSCs/ST-OSCs/I-OSCs.     

A Benzo[1,2-b:4,5-c′]Dithiophene-4,8-Dione-Based Polymer Donor Achieving an Efficiency Over 16%

It is of great significance to develop efficient donor polymers during the rapid development of acceptor materials for nonfullerene bulk-heterojunction (BHJ) polymer solar cells. Herein, a new donor polymer, named PBTT-F, based on a strongly electron-deficient core (5,7-dibromo-2,3-bis(2-ethylhexyl)benzo[1,2-b:4,5-c′]dithiophene-4,8-dione, TTDO), is developed through the design of cyclohexane-1,4-dione embedded into a thieno[3,4-b]thiophene (TT) unit. When blended with the acceptor Y6, the PBTT-F-based photovoltaic device exhibits an outstanding power conversion efficiency (PCE) of 16.1% with a very high fill factor (FF) of 77.1%. This polymer also shows high efficiency for a thick-film device, with a PCE of ≈14.2% being realized for an active layer thickness of 190 nm. In addition, the PBTT-F-based polymer solar cells also show good stability after storage for ≈700 h in a glove box, with a high PCE of ≈14.8%, which obviously shows that this kind of polymer is very promising for future commercial applications. This work provides a unique strategy for the molecular synthesis of donor polymers, and these results demonstrate that PBTT-F is a very promising donor polymer for use in polymer solar cells, providing an alternative choice for a variety of fullerene-free acceptor materials for the research community.     

Side Chain Engineering on Medium Bandgap Copolymers to Suppress Triplet Formation for High‐Efficiency Polymer Solar Cells

Suppression of carrier recombination is critically important in realizing high‐efficiency polymer solar cells. Herein, it is demonstrated difluoro‐substitution of thiophene conjugated side chain on donor polymer can suppress triplet formation for reducing carrier recombination. A new medium bandgap 2D‐conjugated D–A copolymer J91 is designed and synthesized with bi(alkyl‐difluorothienyl)‐benzodithiophene as donor unit and fluorobenzotriazole as acceptor unit, for taking the advantages of the synergistic fluorination on the backbone and thiophene side chain. J91 demonstrates enhanced absorption, low‐lying highest occupied molecular orbital energy level, and higher hole mobility, in comparison with its control polymer J52 without fluorination on the thiophene side chains. The transient absorption spectra indicate that J91 can suppress the triplet formation in its blend film with n‐type organic semiconductor acceptor m ‐ITIC (3,9‐bis(2‐methylene‐(3‐(1,1‐dicyanomethylene)‐indanone)‐5,5,11,11‐tetrakis(3‐hexylphenyl)‐dithieno[2,3‐d:2,3′‐d′]‐s‐indaceno[1,2‐b:5,6‐b′]‐dithiophene). With these favorable properties, a higher power conversion efficiency of 11.63% with high V _OC of 0.984 V and high J _SC of 18.03 mA cm^?2 is obtained for the polymer solar cells based on J91 /m ‐ITIC with thermal annealing. The improved photovoltaic performance by thermal annealing is explained from the morphology change upon thermal annealing as revealed by photoinduced force microscopy. The results indicate that side chain engineering can provide a new solution to suppress carrier recombination toward high efficiency, thus deserves further attention.     

Organic-Salt-Assisted Crystal Growth and Orientation of Quasi-2D Ruddlesden–Popper Perovskites for Solar Cells with Efficiency over 19%

Quasi-2D Ruddlesden–Popper (RP) perovskite solar cells (PSCs) have drawn significant attention due to their appealing environmental stability compared to their 3D counterparts. However, the relatively low power conversion efficiency (PCE) greatly limits their applications. Here, high photovoltaic performance is demonstrated for quasi-2D RP PSCs using 2-thiophenemethylammonium as spacer with nominal n-value of 5, which is based on the stoichiometry of the precursors. The incorporation of formamidinium (FA) in quasi-2D RP perovskites reduces the bandgap and improves the light absorption ability, resulting in enlarged photocurrent and an increased PCE of 16.18%, which is higher than that of reported analogous methylammonium (MA)-based quasi-2D PSC (≈15%). A record high PCE of 19.06% is further demonstrated by using an organic salt, namely, 4-(trifluoromethyl)benzylammonium iodide, assisted crystal growth (OACG) technique, which can induce the crystal growth and orientation, tune the surface energy levels, and suppress the charge recombination losses. More importantly, the devices based on OACG-processed quasi-2D RP perovskites show remarkable environmental stability and thermal stability, for example, the PCE retaining ≈96% of its initial value after storage at 80 °C for 576 h, while only ≈37% of the original efficiency left for FAPbI₃-based 3D PSCs.