Recent progress in the study of zeaxanthin dipalmitate

153

The rapid development of organic synthetic chemistry has led to an extraordinary diversity in the structure and properties of organic semiconductor materials. [1][2][3][4] It is widely accepted that a subtle structural change is able to lead to dramatic property Generally, highly efficient organic solar cells require both a high open-circuit voltage (V OC ) and a high short-circuit current density (J SC ). Reducing the energy loss (E loss ) is an effective way to achieve a high V OC without compromising the photocurrent, which is ideal for enhancing the power conversion efficiencies (PCEs). Herein, a new chlorinated nonfullerene acceptor (ITC-2Cl) with chlorinated thiophene-fused end groups is developed. In comparison with the unchlorinated counterpart (ITCPTC), the introduction of Cl improves not only the electronic properties by redshifting the absorption spectra and deepening the lowest unoccupied molecular orbital energy levels, but also the molecular packing and thus thin-film morphology. The PM6:ITC-2Cl-based device yields a significantly higher PCE (13.6%) with a lower E loss (0.67 eV) than the ITCPTCbased device (PCE of 12.3% with E loss of 0.70 eV). More importantly, compared to the archetypal nonfullerene acceptors such as IT-4F (PCE of 12.9% with E loss of 0.73 eV) and IT-4Cl (PCE of 12.7% with E loss of 0.76 eV), the ITC-2Cl-based device shows a higher PCE and a lower E loss . These results demonstrate that the chlorinated thiophene-fused end group is a promising candidate for a highperformance nonfullerene acceptors with low energy loss.

Section: Methodsmentioning

confidence: 99%

Reduced Energy Loss Enabled by a Chlorinated Thiophene‐Fused Ending‐Group Small Molecular Acceptor for Efficient Nonfullerene Organic Solar Cells with 13.6% Efficiency

Luo

Liu

Wang

et al. 2019

153

“…However, fullerene derivatives suffer from high preparation cost, weak absorptions, and hard tunable energy levels . Recent years, nonfullerene acceptors (NFAs), especially those acceptor–donor–acceptor (A–D–A) type small molecule NFAs, with advantages of good light absorption, facile synthesis, and fine‐tuned energy levels, have drawn great attentions and PCEs over 14% have achieved through the materials innovation, morphology control, and device optimization…”

Section: Photovoltaic Parameters For the Drcn5t:f‐0cl Drcn5t:f‐1cl mentioning

confidence: 99%

High‐Performance All‐Small‐Molecule Solar Cells Based on a New Type of Small Molecule Acceptors with Chlorinated End Groups

Wang

Kan

et al. 2018

On the other hand, the electron donor materials could generally be divided into two categories: polymers and small mole cules. Both types of donors have showed high performance with PCE over 11% in combination with fullerene acceptors. [6,8] Nevertheless, for NFAbased OSCs with high efficiencies, most donor materials are widebandgap polymers [24][25][26][27] and only a few small molecule donors [28][29][30][31] work well with several very limited NFAs. In consideration of the unique advantages of small molecule materials, [32,33] such as welldefined structure and thus less batchtobatch variation, versatile chemical structures and thus easier energy level control, much efforts have been made to develop allsmallmolecule (ASM) OSCs, which comprise small molecule donor and nonfullerene small molecule acceptor. Presently, promising PCEs with value over 10% have been achieved by Li and Hou's groups. [30,34,35] But so far, the electron acceptors with decent performance used in the reported ASMOSCs have only been found in the case of (2,2′[(4,4,9,9tetrahexyl4,9dihydrosindaceno[1,2b:5,6b′] dithiophene2,7 diyl)bis[methylidyne(3oxo1Hindene2,1(3H) diylidene)]]bispropanedinitrile) (IDIC). [36] Considering the versatile chemical structures and thus easier energy level control of small molecules for OSCs, it is highly possible and even better high performing acceptors could be designed and developed for ASMOSCs.Recently, our group has reported an A-D-A type small mole cule acceptor, 2,9bis(2methylene (3(1,1dicyanomethylene) indanone))7,12dihydro4,4,7,7,12,12hexaoctyl4H cyclopenta[2″,1″:5,6;3″,4″:5′,6′]diindeno[1,2b:1′,2′b′] dithiophene (FDICTF, F0Cl in Figure 1) and PCE over 10% has been achieved using widebandgap polymer PBDBT as the donor. [37] To further tune its band structure and morphology in active layer, another acceptor F1Cl through introduction of one chlorine atom on the end groups of F0Cl was developed and a PCE over 11% was obtained for the devices based on PBDB T:F1Cl, which was attributed to the redshifted absorption, enhanced molecular packing, and electron mobility of F1Cl. [38] Encouraged by the success of polymer donor devices, acceptor F1Cl might be a good choice for ASM OSCs. Just recently, it has been reported that acceptors with high crystallinity are favorable in ASMOSCs. [39][40][41] Whether the crystallinity of F1ClWhile a wide variety of nonfullerene acceptors are developed and perform well in combination with polymer donors, only a few nonfullerene acceptors can work well with small molecule donors. Here, all-small-molecule solar cells with high performance enabled by a new type of small molecule acceptors (F-0Cl, F-1Cl, and F-2Cl), which contain linear alkyl side chains and end groups substituted with various number of chlorine atoms, are reported. End group chlorination leads to redshifted absorption, enhanced crystallinity, and high electron mobility. These properties make them competitive as electron acceptors for all-small-molecule solar devices. When combined with two popular small molecule don...

“…OSCs are one of the emerging photovoltaic technologies and have drawn intensive attention in the past two decades. Thanks to concerted efforts dedicated to materials synthesis and device optimization, the PCEs of OSCs based on FREAs and polymer donors have reached 14% . Compared to silicon‐based solar cells, one unique merit of OSCs is their semitransparency, which will enable them specific applications, such as power‐generating windows for building integrated photovoltaics and photovoltaic vehicles.…”

Section: Conclusion and Perspectivementioning

confidence: 99%

“…Therefore, the development of OSCs is now focused on nonfullerene acceptors . The two most promising nonfullerene acceptor classes are rylene diimide‐based materials (PCEs as high as 9–10%) and fused‐ring electron acceptors (FREAs) (PCEs as high as 12–14%) …”

Section: Introductionmentioning

confidence: 99%

Nonfullerene Acceptors for Semitransparent Organic Solar Cells

Dai

Zhan

2018

173

110

The FF is defined as the ratio of the maximum power (P max ) divided by the product of V OC and J SCThe second important parameter of ST-OSCs is transparency. The transparency or transmittance of ST-OSCs is usually characterized by measuring the average visible transmittance (AVT) of the device in the visible region (370-740 nm) with UV-vis spectrophotometer. The requirement of AVT is up to real applications, for example, an AVT of 25% is a basic requirement for the window application. [47] Color is the third parameter of ST-OSCs, which is determined by the photoactive layers and electrodes. CIE 1931 xy chromaticity diagram [53] can be used to characterize the color properties of ST-OSCs. The color coordinate (x,y) of ST-OSCs is calculated from the corresponding transmitted light. The color rendering property is the fourth parameter of ST-OSCs. Generally, the color rendering property is determined by color rendering index (CRI). CRI is an indicator of neutral color degree, which can be calculated from the transmitted light. [54] To realize semitransparency of OSCs, both electrodes must be transparent, allowing not only the light to get in, but also the visible light to partially pass through. A number of transparent electrodes were reported, such as indium tin oxide (ITO), thin metals (Ag or Au), [55][56][57][58][59] poly(ethylenedioxythiophene):poly(st yrene-sulfonate) (PEDOT:PSS), [60][61][62] Ag nanowires, [63][64][65][66][67] and graphene. [68,69] Because there are a couple of reviews focused on the transparent electrodes, [47,52] we will not discuss transparent electrodes in this Research News.Since there is a compromise between the PCE and the AVT of ST-OSCs, in order to achieve high PCE and high AVT simultaneously, an ideal active layer should have strong nearinfrared (NIR) absorption but weak visible absorption. This kind of active layer can sufficiently utilize NIR solar irradiation to achieve high PCE, while maintain high transparency of visible light. Very recently, ST-OSCs based on narrow-band-gap polymer donors and narrow-band-gap nonfullerene acceptors exhibited PCEs up to >10%. [70] However, ST-OSCs were mainly based on blends of fullerene acceptors and poly(3-hexylthiophene) (P3HT) and exhibited low PCEs (<3%) with lower J SC at the early stage. [71,72] In order to extend absorption of the active layer and enhance the J SC of OSCs, a number of donors with medium and low band gaps have been synthesized (Figure 1), and their absorption edges extend from 600 nm (P3HT) to NIR region, [73][74][75][76][77][78][79][80][81][82][83] for instance, PBDTTT-C-T, [84] PTB7, [85][86][87] Semitransparent organic solar cells (ST-OSCs) have appealing features, such as flexibility, transparency, and color in addition to generating clean energy, and therefore show potential applications in building integrated photovoltaics and photovoltaic vehicles. Concerted efforts in materials synthesis (particularly low-band-gap polymer donors and nonfullerene acceptors) and device optimization (particularly incorporating transpa...