Thieno[3,2‐b][1]benzothiophene Derivative as a New π‐Bridge Unit in D–π–A Structural Organic Sensitizers with Over 10.47% Efficiency for Dye‐Sensitized Solar Cells

Three new thieno[3,2‐b][1]benzothiophene ( TBT )‐based donor–π–acceptor (D–π–A) sensitizers, coded as SGT ‐ 121 , SGT ‐ 129 , and SGT ‐ 130 , have been designed and synthesized for dye‐sensitized solar cells (DSSCs), for the first time. The TBT , prepared by fusing thiophene unit with the phenyl unit of triphenylamine donor, is utilized as the π‐bridge for all sensitizers with good planarity. They have been molecularly engineered to regulate the highest occupied molecular orbital (HOMO)‐lowest unoccupied molecular orbital (LUMO) energy levels and extend absorption range as well as to control the electron‐transfer process that can ensure efficient dye regeneration and prevent undesired electron recombination. The photovoltaic performance of SGT‐sensitizer‐based DSSCs employing Co(bpy)₃^2+/3+ (bpy = 2,2′‐bipyridine) redox couple is systematically evaluated in a thorough comparison with Y123 as a reference sensitizer. Among them, SGT ‐ 130 with benzothiadiazole‐phenyl ( BTD ‐ P ) unit as an auxiliary acceptor exhibits the highest power‐conversion efficiency (PCE) of 10.47% with J_sc = 16.77 mA cm^?2, V_oc = 851 mV, and FF = 73.34%, whose PCE is much higher than that of Y123 (9.5%). It is demonstrated that the molecular combination of each fragment in D–π–A organic sensitizers can be a pivotal factor for achieving the higher PCEs and an innovative strategy for strengthening the drawbacks of the π‐bridge.     

Porphyrin Sensitizers with Donor Structural Engineering for Superior Performance Dye‐Sensitized Solar Cells and Tandem Solar Cells for Water Splitting Applications

Zn(II)–porphyrin sensitizers, coded as SGT‐020 and SGT‐021 , are designed and synthesized through donor structural engineering. The photovoltaic (PV) performances of SGT sensitizer‐based dye‐sensitized solar cells (DSSCs) are systematically evaluated in a thorough SM315 as a reference sensitizer. The effect of the donor ability and the donor bulkiness on photovoltaic performances is investigated for establishing the structure–performance relationship in the platform of porphyrin‐triple bond‐benzothiadiazole‐acceptor sensitizers. By introducing a more bulky fluorene unit to the amine group in the SM315 , the power conversion efficiency (PCE) is enhanced with the increased short‐circuit current (J_sc) and open‐circuit voltage (V_oc), due to the improved light‐harvesting ability and the efficient prevention of charge recombination, respectively. As a consequence, a maximum PCE of 12.11% is obtained for SGT‐021 , whose PCE is much higher than the 11.70% PCE for SM315 . To further improve their maximum efficiency, the first parallel tandem DSSCs employing cobalt electrolyte in the top and bottom cells are demonstrated and an extremely high efficiency of 14% is achieved, which is currently the highest reported value for tandem DSSCs. The series tandem DSSCs give a remarkably high V_oc value of >1.83 V. From this DSSC tandem configuration, 7.4% applied bias photon‐to‐current efficiency is achieved for solar water splitting.     

Solid‐State Dye‐Sensitized Solar Cells Using a Novel Class of Ullazine Dyes as Sensitizers

Here we present the photovoltaic performance of solid‐state dye‐sensitized solar cells (DSCs) using a series of ullazine‐based metal‐free organic sensitizers and spiro‐MeOTAD as a hole‐transport material. A maximum of 4.95% power conversion efficiency measured under standard AM 1.5G illumination (100 mW cm^?2) was achieved with the best performing ullazine dye, and was further improved to 5.40% through co‐sensitization with the triphenylamine‐based organic sensitizer, D35. This study investigates the effect of the molecular structure of the ullazine sensitizer on the performance in solid‐state DSCs.     

The Role of Antireflective Coating CYTOP,Immersion Oil,and Sensitizer Selection in Fabricating a 2.3 V, 10% Power Conversion Efficiency SSM‐DSC Device

Sequential series multijunction dye‐sensitized solar cells (SSM‐DSCs) can power solar‐to‐fuel processes with a single illuminated area device. Dye selection and strategies limiting photon losses are critical in SSM‐DSC devices for higher performance systems. Herein, an efficient and readily applicable spin coating protocol on glass surfaces with an antireflective fluoropolymer (CYTOP) is applied to an SSM‐DSC architecture. Combining CYTOP with the use of an immersion oil between glass spacers in a three subcell SSM‐DSC with judiciously selected TiO₂ photoanode sensitizers and thicknesses, an overall power conversion efficiency (PCE) of 10.1% is obtained with an output of 2.3 V. Without external bias, this SSM‐DSC configuration shows an impressive overall solar‐to‐fuel conversion efficiency of 6% when powering IrO₂ and Au₂O₃ electrocatalysts for CO₂ and H₂O to CO and H₂ conversion in aqueous solution. The role of CYTOP, immersion oil, sensitizer selection, and film thickness on SSM‐DSC devices is discussed along with the stability of this system.     

Extended π‐Bridge in Organic Dye‐Sensitized Solar Cells: the Longer,the Better?

The elongation of π‐conjugated bridges between the donor (D) and the acceptor (A) represents a feasible strategy towards enhancement of light‐harvesting in both breadth and depth of organic D‐π‐A dyes suitable for nanocrystalline TiO₂‐based dye‐sensitized solar cells (DSSCs). Here, a series of organic dyes with elongating conjugated bridges is synthesized and characterized. DSSC devices employing a cobalt (II/III) redox electrolyte are fabricated using these dyes as light‐harvesting sensitizers. Compared to a dye with the 3,4‐ethylenedioxythiophene (EDOT) linker ( G188 ), the three counterparts with further extended π‐bridges present gradually red‐shifted electronic absorption spectra and a persistent decrease in oxidation potential. The photocurrent action spectra show that the extension of π‐conjugated bridges decreases the open‐circuit photovoltage. The best performance is shown in G268 with a short‐circuit photocurrent density (J_sc) of 16.27 mA cm², an open‐circuit photovoltage (V_oc) of 0.83 V, and a fill factor (FF) of 0.67, corresponding to an overall conversion efficiency of 9.24%. Unexpectedly, G270, which has with the longest π‐bridge , showed the lowest J_sc, V_oc, and efficiency.     

Indolizine‐Based Donors as Organic Sensitizer Components for Dye‐Sensitized Solar Cells

Strong electron‐donating functionality is desirable for many organic donor‐π‐bridge‐acceptor (D‐π‐A) dyes. Strategies for increasing the electron‐donating strength of common nitrogen‐based donors include planarization of nitrogen substituents and the use of low resonance‐stabilized energy aromatic ring‐substituted nitrogen atoms. Organic donor motifs based on the planar nitrogen containing heterocycle indolizine are synthesized and incorporated into dye‐sensitized solar cell (DSC) sensitizers. Resonance active substitutions at several positions on indolizine in conjugation with the D‐π‐A π‐system are examined computationally and experimentally. The indolizine‐based donors are observed to contribute electron density with strengths greater than triarylamines and diarylamines, as evidenced by UV/Vis, IR absorptions, and oxidation potential measurements. Fluorescence lifetime studies in solution and on TiO₂ yield insights in understanding the performance of indolizine‐based dyes in DSC devices.     

Atomic Layer Deposition of CdS Quantum Dots for Solid‐State Quantum Dot Sensitized Solar Cells

Functioning quantum dot (QD) sensitized solar cells have been fabricated using the vacuum deposition technique atomic layer deposition (ALD). Utilizing the incubation period of CdS growth by ALD on TiO₂, we are able to grow QDs of adjustable size which act as sensitizers for solid‐state QD‐sensitized solar cells (ssQDSSC). The size of QDs, studied with transmission electron microscopy (TEM), varied with the number of ALD cycles from 1‐10 nm. Photovoltaic devices with the QDs were fabricated and characterized using a ssQDSSC device architecture with 2,2',7,7'‐tetrakis‐(N,N‐di‐p methoxyphenylamine) 9,9'‐spirobifluorene (spiro‐OMeTAD) as the solid‐state hole conductor. The ALD approach described here can be applied to fabrication of quantum‐confined structures for a variety of applications, including solar electricity and solar fuels. Because ALD provides the ability to deposit many materials in very high aspect ratio substrates, this work introduces a strategy by which material and optical properties of QD sensitizers may be adjusted not only by the size of the particles but also in the future by the composition.     

Similar or Totally Different: the Adjustment of the Twist Conformation Through Minor Structural Modification,and Dramatically Improved Performance for Dye‐Sensitized Solar Cell

A novel approach for enhancing the performance of dye‐sensitized solar cells is presented. It is based on the analysis of five sensitizers by utilizing triarylamine as donor, thiophene benzothiadiazole as chromophore and substituted thienyl linked with cyanoacrylic acid as the anchoring group (LI‐80‐LI‐84). Accompanied with the increasing steric hindrance of the substituents on the thienyl isolation group, the conformation of the dyes, in particular the angle between the chromophore and the anchoring group, becomes more and more twisted. Surprisingly, sensitizers with poorer conjugation effects (the higher twisted conformation) achieve better photovoltaic performances, showing a contrary trend to the traditional donor‐(π‐spacer)‐acceptor dyes with a better co‐planarity. On the basis of the preceding fundamental comprehensions, an empirical method is successfully applied to a new phenyl‐based system (LI‐85 and LI‐86) to improve their performances. The systematical investigation indicates that the twisted structures can contribute to the E_CB of the TiO₂ film, electron lifetime and resistance at the TiO₂/dye/electrolyte interface. Thereby, the efficiency of the initial LI‐80‐based cell has been dramatically improved to 2.45 times higher for LI‐86‐based cell, paving a new way for the design of better sensitizers with higher device performances.     

Donor functionalized quinoline based organic sensitizers for dye sensitized solar cell (DSSC) applications: DFT and TD-DFT investigations

The influence of different donor groups in quinoline based novel sensitizers for dye sensitized solar cell (DSSC) applications is analyzed by using density functional theory (DFT) and time dependent density functional theory (TD-DFT). Quinoline and donor functionalized quinoline based novel organic sensitizers have been designed with different π-spacers for DSSC applications. The ground state molecular structure of novel organic sensitizers is fully optimized by DFT calculation in both gas and chloroform phases. Electronic absorption characteristics are predicted by the TD-DFT calculation in both gas and chloroform phases. The polarizable continuum model is used for solvent phase optimization. The net electron transfer from the donor to acceptor is calculated from natural bond orbital (NBO) analysis. The injection energy and dye regeneration energy values are also calculated. Different donor groups are substituted in quinoline, and these substituted quinoline donors are used as the donor group. Cyanovinyl and thiophene groups act as π-spacers and cyanoacrylic acid acts as an acceptor. DFT and TD-DFT studies of the quinoline and donor functionalized quinoline sensitizers show that the coumarin based and N-hexyltetrahydroquinoline donors are more efficient for DSSC application.     

New Acetylene‐Bridged 9,10‐Conjugated Anthracene Sensitizers: Application in Outdoor and Indoor Dye‐Sensitized Solar Cells

In this report, a pivotal improvement in the performance of dye‐sensitized solar cells has been achieved, thus taking it one step closer toward the commercialization. Through the stepwise modification on the anthracene‐based organic sensitizers, the alteration of alkyl to alkoxy chain and incorporation of electron deficient moieties in the new sensitizing dyes TY3 , TY4 , and TY6 are found to play a significant role in the efficiency enhancement. The dye TY6 , when tested under 1 sun (AM 1.5G) illumination, is found to exhibit the best efficiency of 8.08% in the series reported here. Taking it further, sensitizer TY6 achieves a milestone by displaying an efficiency of 28.56% when tested under T5 fluorescent illumination of 6000 lux and 20.72% under same illuminance from a commercial light emitting diode light source. Such an excellent performance can be attributed to its outstanding J _SC and V _OC, which are characteristic properties of these anthracene dyes.     

Sensitized photomodification of DNA with binary systems of oligonucleotide conjugates. V. Effect of the structure of the target DNA. Quantitative photomodification]

A sensitized photomodification of several single-stranded target DNAs by binary systems of oligonucleotide conjugates complementary to the adjacent regions of DNA was performed. One of the conjugates contained a sensitizer (pyrene, anthracene, or 1,2-benzanthracene), and another conjugate contained a photoreagent 4-azidotetrafluorobenzalhydrazone. The sensitized photomodification is initiated by irradiation at 365-580 nm due to effective energy transfer from the excited sensitizer to the photoreagent in a complementary complex of the binary system with the target DNA where the sensitizer and photoreagent are brought sterically together. Conditions for the quantitative photomodification of a single-stranded DNA by the binary system of oligonucleotide conjugates were found. The maximum degree of photomodification depends on the number of guanosine residues in the (pG)n sequence of the target DNA at the modification site: at n = 1 the yield of covalent adducts was 62-68%, at n = 2, 75-82%, and at n = 4, 98-99%.     

Multifunctional Luminescent Down‐Shifting Fluoropolymer Coatings: A Straightforward Strategy to Improve the UV‐Light Harvesting Ability and Long‐Term Outdoor Stability of Organic Dye‐Sensitized Solar Cells

A new multifunctional coating for photovoltaic cells incorporating light‐management, UV‐protection, and easy‐cleaning capabilities is presented. Such coating consists of a new photocurable fluorinated polymer embedding a luminescent europium complex that acts as luminescent down‐shifting (LDS) material converting UV photons into visible light. The combination of this system with ruthenium‐free organic dye‐sensitized solar cells (DSSCs) gives a 70% relative increase in power conversion efficiency as compared with control uncoated devices, which is the highest efficiency enhancement reported to date on organic DSSC systems by means of a polymeric LDS layer. Long‐term (>2000 h) weathering tests in real outdoor conditions reveal the excellent stabilizing effect of the new coating on DSSC devices, which fully preserve their initial performance. This excellent outdoor stability is attributed to the combined action of the luminescent material that acts as UV‐screen and the highly photostable, hydrophobic fluoropolymeric carrier that further prevents photochemical and physical degradation of the solar cell components. The straightforward approach presented to simultaneously improve performance and outdoor stability of DSSC devices may be readily extended to a large variety of sensitizer/luminophore combinations, thus enabling the fabrication of highly efficient and extremely stable DSSCs in an easy and versatile fashion.     

Photodynamic effect of novel chlorin e6 derivatives on a single nerve cell

Chlorin e(6) and its derivatives are promising sensitizers for photodynamic therapy (PDT). In order to compare the photodynamic effects of 8 novel derivatives of chlorin e(6) and to explore some mechanisms of their effects at the cellular level, we studied PDT-induced changes in bioelectric activity of crayfish mechanoreceptor neuron that was used as a sensitive experimental model. Neurons were insensitive to red laser irradiation (632.8 nm; 0.3 W/cm(2)) or to photosensitizers alone, but changed firing rate and died under the photodynamic effect of nanomolar concentrations of sensitizers. The dynamics of neuron responses depended on photosensitizer type and concentration. The dependence of neuron lifetime on photosensitizer concentration allowed comparing efficiencies of different photosensitizers. Radachlorin was the most potent photosensitizer comparable with mTHPC. High photodynamic efficiency of some chlorin e(6) derivatives was related to weak dependence of neuron lifetime on sensitizer concentration, indicating to the initiation of 2-3 secondary processes such as free radical membrane damage by one absorbed photon. Photodynamic efficiency of sensitizers depended on amphiphilicity influencing their intracellular localization.     

A Halogenation Strategy for over 12% Efficiency Nonfullerene Organic Solar Cells

Three acceptor–donor–acceptor type nonfullerene acceptors (NFAs), namely, F–F, F–Cl, and F–Br, are designed and synthesized through a halogenation strategy on one successful nonfullerene acceptor FDICTF (F–H). The three molecules show red‐shifted absorptions, increased crystallinities, and higher charge mobilities compared with the F–H. After blending with donor polymer PBDB‐T, the F–F‐, F–Cl‐, and F–Br‐based devices exhibit power conversion efficiencies (PCEs) of 10.85%, 11.47%, and 12.05%, respectively, which are higher than that of F–H with PCE of 9.59%. These results indicate that manipulating the absorption range, crystallinity and mobilities of NFAs by introducing different halogen atoms is an effective way to achieve high photovoltaic performance, which will offer valuable insight for the designing of high‐efficiency organic solar cells.     

Perylene Sensitization of Fullerenes for Improved Performance in Organic Photovoltaics

We present the addition of an energy relay dye to fullerenes resulting in increased light harvesting and significantly improved power conversion efficiency for organic photovoltaic (OPV) devices. Although exhibiting excellent properties as electron acceptors, visible light absorption of fullerenes is limited. Strongly light absorbing donor materials are needed for efficient light harvesting in the thin active layer of OPV devices. Therefore, photocurrent generation and thus power conversion efficiency of this type of solar cell is confined by the overlap of the relatively narrow absorption band of commonly used donor molecules with the solar spectrum. Herein the concept of fullerene dye sensitization is presented, which allows increased light harvesting on the electron acceptor side of the heterojunction. The concept is exemplarily shown for an UV absorbing small molecule and a near infrared absorbing polymer, namely hexa‐peri‐hexabenzocoronene (HBC) and Poly[2,1,3‐benzothiadiazole‐4,7‐diyl[4,4‐bis(2‐ethylhexyl)‐4H‐cyclopenta[2,1‐b:3,4‐b']dithiophene‐2,6‐diyl]] (PCPDTBT), respectively. In both systems remarkably higher power conversion efficiency is achieved via perylene sensitization of the fullerene acceptor. Steady state photoluminescence, transient absorption and transient photocurrent decay studies reveal pathways of the additionally generated excited states at the sensitizer molecule. The findings suggest fluorescence resonance energy transfer from the photo‐excited dye to the fullerene enabling decoupling of light absorption and charge transport. The presented sensitization method is proposed as a viable new concept for performance enhancement in organic photovoltaic devices.     

Integrated Design of Organic Hole Transport Materials for Efficient Solid‐State Dye‐Sensitized Solar Cells

A series of triphenylamine‐based small molecule organic hole transport materials (HTMs) with low crystallinity and high hole mobility are systematically investigated in solid‐state dye‐sensitized solar cells (ssDSCs). By using the organic dye LEG4 as a photosensitizer, devices with X3 and X35 as the HTMs exhibit desirable power conversion efficiencies (PCEs) of 5.8% and 5.5%, respectively. These values are slightly higher than the PCE of 5.4% obtained by using the state‐of‐the‐art HTM Spiro‐OMeTAD. Meanwhile, transient photovoltage decay measurement is used to gain insight into the complex influences of the HTMs on the performance of devices. The results demonstrate that smaller HTMs induce faster electron recombination in the devices and suggest that the size of a HTM plays a crucial role in device performance, which is reported for the first time.     

Photorelease of carboxylic and amino acids from N-methyl-4-picolinium esters by mediated electron transfer.

One electron reduction of N-alkyl-4-picolinium (NAP) esters initiates C-O bond scission releasing a carboxylate anion. Previous experiments have demonstrated that this process can be initiated by photoinduced electron transfer from an electron-donating sensitizer. In the present study it is demonstrated that a comparable photorelease process can be initiated by photolysis of an electron acceptor (mediator), which in turn abstracts an electron from a ground state electron donor. The resulting mediator anion radicals donate an electron to the NAP ester, triggering release of the carboxylate anion. It is demonstrated that when benzophenone is used as a mediator, higher quantum yields for ester decomposition can be achieved compared with sensitizers that do direct photoinduced electron transfer.     

Investigation into the influence of an acrylic acid acceptor in organic D-π-A sensitizers against phototoxicity

Photodynamic therapy (PDT) is a non-invasive, selective, and cost-effective cancer therapy. We previously reported that thiophene-based organic D-π-A sensitizers consist of an electron-donating (D) moiety, a π-conjugated bridge (π) moiety, and an electron-accepting (A) moiety, and are readily accessible and stable templates for photosensitizers that could be used in PDT. In addition, acrylic acid acceptor-containing photosensitizers exert a high level of phototoxicity. This study was an investigation into 1) the possibility of increasing phototoxicity by introducing another carboxyl group or by replacing a carboxyl group with a pyridinium group, and 2) the importance of an alkene in the acrylic acid acceptor for phototoxicity. A review of the design, synthesis, and evaluation of sensitizers revealed that neither dicarboxylic acid nor pyridinium photosensitizers enhance phototoxicity. An evaluation of a photosensitizer without an alkene in the acrylic acid moiety revealed that the alkene was not indispensable in the pursuit of phototoxicity. The obtained results provided new insight into the design of ideal D-π-A photosensitizers for PDT.     

Bis(Naphthalene Imide)diphenylanthrazolines: A New Class of Electron Acceptors for Efficient Nonfullerene Organic Solar Cells and Applicable to Multiple Donor Polymers

Unlike universally applicable fullerene derivatives, current nonfullerene electron acceptors are rarely effective with more than one donor polymer in bulk heterojunction (BHJ) solar cells. A novel class of nonfullerene electron acceptors, bis(naphthalene imide)‐3,6‐diphenyl‐trans‐anthrazolines (BNIDPAs), that is applicable and yields efficient photovoltaic devices with multiple donor polymers, including a thiazolothiazole–dithienosilole copolymer (PSEHTT) and benzodithiophene copolymers (PBDTT‐FTTE and PTB7) is reported. Photovoltaic devices composed of the BNIDPA‐butyloctyl (BO) acceptor with PSEHTT, PBDTT‐FTTE, and PTB7, respectively, have power conversion efficiencies of 3.0%–3.1% with high open‐circuit voltages of ≈1.0 V. In contrast, BHJ devices composed of BNIDPA‐DT acceptor with larger 2‐decyltetradecyl chains and the same donor polymers have substantially reduced bulk electron mobility and reduced photovoltaic efficiencies of 1.3%–1.7%, which highlight the critical role of the size of alkyl chains appended onto nonfullerene electron acceptors. The present results provide a rare example of nonfullerene electron acceptors that are capable of pairing with multiple donor polymers to achieve efficient BHJ solar cells.     

High‐Performance,Transparent, Dye‐Sensitized Solar Cells for See‐Through Photovoltaic Windows

Dye‐sensitized solar cells (DSCs) have attracted great interest as one of the most promising photovoltaic technologies, and transparent DSCs show potential applications as photovoltaic windows. However, the competition between light absorption for photocurrent generation and light transmittance for obtaining high transparency limits the performance of transparent DSCs. Here, transparent DSCs exhibiting a high light transmittance of 60.3% and high energy conversion efficiency (3.66%) are reported. The strategy is to create a cocktail system composed of ultraviolet and near‐infrared dye sensitizers that selectively and efficiently harvest light in the invisible or low‐eye‐sensitivity region while transmitting light in high‐eye‐sensitivity regions. This new design provides a reasonable approach for realizing high efficiency and transparency DSCs that have potential applications as photovoltaic windows.