Highest Occupied Molecular Orbital Level Research Articles

Structural characterization and electronic properties of Ni/rubrene bilayers with alternative stacking sequences.

Recent progress in organic electronics has attracted interest due to their excellent characteristics that include photovoltaic, light emission, and semiconducting behaviours. Spin-induced properties play important roles in organic electronics, while introducing spin into an organic layer in which spin responses, such as a weak spin-orbital coupling and long spin-relaxation time, allows a variety of spintronic applications to be achieved. However, such spin responses are rapidly attenuated by misalignment in the electronic structure of hybrid structures. We report herein on the energy level diagrams of Ni/rubrene bilayers that can be tuned by an alternating stacking. The band edges of the highest occupied molecular orbital (HOMO) levels were determined to be 1.24 and 0.48 eV relative to the Fermi level for Ni/rubrene/Si and rubrene/Ni/Si bilayers, respectively. This raises a possibility of accumulating electric dipoles at the ferromagnetic/organic semiconductor (FM/OSC) interface, which would inhibit the transfer of spin in the OSC layer. This phenomenon is caused by the formation of a Schottky-like barrier in the rubrene/Ni heterostructures. According to the information about the band edges of the HOMO levels, schematic plots of the HOMO shift in the electronic structure of the bilayers are presented. Based on the lower value of the effective uniaxial anisotropy for Ni/rubrene/Si, the uniaxial anisotropy was suppressed compared to that of rubrene/Ni/Si. The characteristics of the formation of Schottky barriers at the FM/OSC interface have an impact on the temperature-dependent spin states in the bilayers.

Wetting sub-nanochannels via ionic hydration effect for improving charging dynamics

The ionic transport in sub-nanochannels plays a key role in energy storage, yet suffers from a high energy barrier. Wetting sub-nanochannels is crucial to accelerate ionic transport, but the introduction of water is challenging because of the hydrophobic extreme confinement. We propose wetting the channels by the exothermic hydration process of pre-intercalated ions, the effect of which varies distinctly with different ionic hydration structures and energies. Compared to the failed pre-intercalation of SO42−, HSO4− with weak hydration energy results in a marginal effect on the HOMO (Highest Occupied Molecular Orbital) level of water to avoid water splitting during the electrochemical intercalation. Meanwhile, the ability of water introduction is reserved by the initial incomplete dissociation state of HSO4−, so the consequent exothermic reionization and hydration processes of the intercalated HSO4− promote the water introduction into sub-nanochannels, finally forming the stable confined water through hydrogen bonding with functional groups. The wetted channels exhibit a significantly enhanced ionic diffusion coefficient by ∼9.4 times.

Incorporating a weak acceptor unit into PTB7-Th to tune the open circuit voltage for non-fullerene polymer solar cells

PTB7-Th is one of the most effective polymer donors which have drawn huge attention in organic solar cells. However, the highest occupied molecular orbital (HOMO) level of PTB7-Th is relatively high, which limit open circuit voltage (Voc) of the cell devices. In this work, to develop the new members of PTB7-Th family materials with higher Vocs, two new random terpolymers PTB7-Th(0.9) and PTB7-Th(0.8) have been synthesized, in which contains 10% or 20% benzo[1,2-b:4,5-b′]dithiophene-2,6-dicarboxylate (VBDTC, a weak acceptor unit) moiety in PTB7-Th. It was found that the incorporating of VBDTC unit has great influence on optical and electronic properties of the related polymers. Comparison with PTB7-Th, the PTB7-Th(0.9) and PTB7-Th(0.8) exhibit blue shift in the UV−visible spectra, which forming a more complementary absorption with the low band gap non-fullerene acceptors, like ITIC and Y6. Increasing the percentage of VBDTC moiety, it can sufficiently deepen the low-lying HOMO level of the related polymers, which would expect to an enhancement in Voc. Non-fullerene solar cells blended with ITIC, PTB7-Th(0.9) exhibited a Voc of 0.839 V, with power conversion efficiency (PCE) of 4.86%. Interestingly, PTB7-Th(0.8) showed superior photovoltaic performance with a Voc of 0.862 V, and PCE of 5.24%. And when blended with Y6, the PCE of PTB7-Th(0.8) based device was further improved to 6.13%, due to increasing the short-circuit current (Jsc). The comprehensive study reveals that it is an effective strategy to tune the absorption spectra and deepens the HOMO energy level of the PTB7-Th related polymers by incorporation of a weak acceptor unit, thus, achieving higher Voc as well as photovoltaic performance.

Deciphering the Role of Hole Transport Layer HOMO Level on the Open Circuit Voltage of Perovskite Solar Cells

AbstractWith the rapid development of perovskite solar cells, reducing losses in open‐circuit voltage (Voc) is a key issue in efforts to further improve device performance. Here it is focused on investigating the correlation between the highest occupied molecular orbital (HOMO) of device hole transport layers (HTLs) and device Voc. To achieve this, structurally similar HTL materials with comparable optical band gaps and doping levels, but distinctly different HOMO levels are employed. Using light‐intensity dependent Voc and photoluminescence measurements significant differences in the behavior of devices employing the two HTLs are highlighted. Light‐induced increase of quasi‐Fermi level splitting (ΔEF) in the perovskite layer results in interfacial quasi‐Fermi level bending required to align with the HOMO level of the HTL, resulting in the Voc measured at the contacts being smaller than the ΔEF in the perovskite. It is concluded that minimizing the energetic offset between HTLs and the perovskite active layer is of great importance to reduce non‐radiative recombination losses in perovskite solar cells with high Voc values that approach the radiative limit.

Naphthoquinoneoxime-Sensitized Titanium Dioxide Photoanodes: Photoelectrochemical Properties.

Naphthoquinoneoxime derivatives, viz., LwOx, 3-hydroxy-4-(hydroxyimino)naphthalen-1 (4H)-one; PthOx, 3-hydroxy-4-(hydroxyimino)-2-methylnaphthalen-1(4H)-one; and Cl_LwOx, 2-chloro-3-hydroxy-4-(hydroxyimino)naphthalen-1(4H)-one, are used in fabrication of dye-sensitized solar cells (DSSCs). The photophysical and electrochemical properties of the sensitizers were studied. The HOMO-LUMO energy gaps of the sensitizers (LwOx, PthOx, and Cl_LwOx) calculated by using the intersection of UV-visible and fluorescence spectra are 2.85, 2.71, and 2.87 eV, respectively. The energy band alignment energy level of the sensitizer, that is, the lowest unoccupied molecular orbital (LUMO) and highest occupied molecular orbital (HOMO), should match with the energy level of the TiO2 conduction band and the redox potential of iodine/triiodide electrolyte to allow smooth electron transfer. The electrochemical characterization of sensitizers was done to find the LUMO and HOMO level of the sensitizer. It shows that the LUMO level of (LwOx, PthOx, and Cl_LwOx) is above the conduction band position of TiO2. Electrochemical impedance spectroscopy was used to study the charge transport resistance and electron lifetime of DSSCs. The charge transport resistance at the TiO2 |electrolyte|counter electrode interface was reduced in the Cl_LwOx device; thus, the electron lifetime of Cl_LwOx was enhanced compared to LwOx and PthOx sensitizers. The fabricated device was characterized using photocurrent density-voltage (J-V) measurement. It is observed that there was an enhancement in the overall power conversion efficiency (η) of the DSSCs fabricated by using Cl_LwOx sensitizers as compared to LwOx and PthOx sensitizer-loaded photoanodes. Enhancement in power conversion efficiency, that is, photovoltage and photocurrent, is achieved due to the chlorine substituent. Thus, the chlorine substituent naphthoquinoneoxime pushes the electron density, enhancing the pushing nature and facilitating the lone pair present in the N-OH moiety to attach to TiO2 more strongly.

A potential sensor for assessing thorium (IV) based on Albuterol sulfate fluorescence enhancement: A density functional theory (DFT) study

• Introducing a new fluorescent sensor for assessing Th(IV) in environmental samples. • Fluorescence mechanism was discussed. • HOMO and LUMO energy levels has been calculated by DFT. This study introduces a potential fluorescence sensor for assessing thorium (Th(IV)) in aquatic environments. In the presence of Th(IV), Albuterol Sulfate ( ABS ) 4-[2-( tert -butylamino)-1-hydroxyethyl]-2-(hydroxymethyl)phenol; sulfuric acid exhibits significant fluorescence enhancement at 600 nm. The current ABS ligand sensor shows wide linear range from 6.0 × 10 −8 – 2.5 × 10 −7 mol/L and pH range of 4–6. Interestingly, when all evaluated interference ions coexisted, the change in fluorescence emission intensity of ABS -Th complex was roughly 2.3 %. The binding mode is studied and indicating a 2:1 complex formation between ABS ligand and Th (IV). Density functional theory (DFT) has been utilized to examine the interaction characteristics between the present ABS ligand sensor and Th(IV) and to compute the geometric configuration of the ABS and ABS -Th through the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) energy levels. The interaction properties exhibit considerable effect on the HOMO and LUMO properties of the complexes, as well as a fluorescence enhancement that could be attributable to the heavy atom effect of Th (IV). The ABS sensor shows remarkable features and provides good performance compared to some of the optical sensors, making it a potential new fluorescence sensor for Th(IV) assessment.

Efficient ternary organic solar cells with BT-rhodanine-based nonfullerene acceptors in a PM6:Y6-BO blend

A series of benzothiadiazole (BT)–rhodanine-based nonfullerene acceptors (NFAs) were designed and synthesized. These BT–rhodanine-based NFAs were composed of BT as a central core with a 3-octylthienothiohene π-bridge and two different rhodanine end groups (BT-rho for octylrhodanine and BT-rhoCN for dicyano-octylrhodanine end groups). The highest occupied molecular orbital (HOMO)/lowest unoccupied molecular orbital (LUMO) levels were −5.53/−3.78 eV for a BT-rho film and −5.63/−3.90 eV for a BT-rhoCN film. The strong electron-withdrawing dicyano-octylrhodanine end group of BT-rhoCN downshifted the HOMO and LUMO levels by ∼0.1 eV compared with those of BT-rho. The 10% BT-rho in a PM6:Y6-BO ternary organic solar cell exhibit a maximum power conversion efficiency (PCE) of 16.17% with a short-circuit current density ( J SC ) of 25.29 mA cm −2 , open-circuit voltage ( V OC ) of 0.84 V, and fill factor ( FF ) of 76.13%. The hole/electron mobilities of the PM6:Y6-BO, 10% BT-rho, and 10% BT-rhoCN ternary devices were 2.20 × 10 −4 /1.85 × 10 −4 cm 2 V −1 s −1 , 3.66 × 10 −4 /3.77 × 10 −4 cm 2 V −1 s −1 , and 1.34 × 10 −4 /0.94 × 10 −4 cm 2 V −1 s −1 , respectively. The crystal coherence lengths ( L C s) of the (010) peaks for the PM6:Y6-BO, 10% BT-rho, and 10% BT-rhoCN ternary films are 43.2, 60.8, and 33.7 Å, respectively. The superior PCE of the 10% BT-rho ternary devices compared with that of the PM6:Y6-BO binary device is attributed to the enhanced hole and electron mobilities and the high crystallinity of the blend films, which contribute to the enhancement of the J SC and PCE. • New BT-based acceptors, BT-rho and BT-rhoCN, were synthesized by inserting rhodanine terminal groups. • Rhodanine end groups of BT-rho lowered the LUMO level and thus increased the open-circuit voltage. • An enhanced PCE of 16.17% was achieved using BT-rho as a third component in a PM6:Y6-BO blend.

Designing and theoretical characterization of D-π-A1-π-A2 typed organic small molecule donor materials

A few of novel D-π-A1-π-A2 typed asymmetric organic small molecules (OSMs) named BT-CN, BT-P, BT-P-2F and BT-P-2F–CN were designed theoretically, by a 1,3-indanone (IDO) substitution, independent and synergistic modification of malononitrile group and F atoms on the A2 unit of the reported BT-2 structure, which is based on triphenylamine (TPA) as electron-donating group, 5,6-difluoro-2,1,3-benzothiadiazole (FFBT) as electron-withdrawing core. The molecular structures, frontier molecular orbitals, UV–vis absorption spectra, atomic charges, energy loss (Eloss) and charge transfer properties of these OSMs were calculated by quantum chemistry method. The effects of terminal substitution and modification on the molecular structure and photovoltaic properties were further explored. As a result, in contrast to BT-2 (A2 = 3-hexyl rhodamine), BT-P (A2 = 1, 3- indene diketone) has the same band gap (Eg) and highest occupied molecular orbital (HOMO) level, but better planarity and charge transfer properties; Compared to BT-2 and BT-P, BT-CN and BT-P-2F not only achieve more narrowed Eg values and deeper HOMO levels, but also get better charge transfer properties via independent modification with malononitrile group and F atoms; Notably, BT-P-2F–CN has the most narrowed Eg, the lowest deep-lying HOMO, the best charge transfer properties and smallest Eloss, due to synergistic effects of malononitrile group and F atoms. The power conversion efficiencies (PCEs) of 5.0%, 5.8% and 8.3% have been performed by the photovoltaic devices for BT-P-2F/PC61BM, BT-CN/PC61BM and BT-P-2F–CN/PC61BM systems, respectively, based on Scharber models. On the basis of the results, BT-P-2F, BT-CN and BT-P-2F–CN would be proposed as potential high performance donor materials of asymmetric OSMs based on TPA-BT backbone. This study could provide a useful theoretical guide for molecular design for high performance organic solar cells.

Towards Efficient Blue Delayed-Fluorescence Molecules by Modulating Torsion Angle Between Electron Donor and Acceptor

Towards Efficient Blue Delayed-Fluorescence Molecules by Modulating Torsion Angle Between Electron Donor and Acceptor

Phosphonium-Based Ionic Thermally Activated Delayed Fluorescence Emitters for High-Performance Partially Solution-Processed Organic Light-Emitting Diodes

Phosphonium-Based Ionic Thermally Activated Delayed Fluorescence Emitters for High-Performance Partially Solution-Processed Organic Light-Emitting Diodes

Efficient Selective Sorting of Semiconducting Carbon Nanotubes Using Ultra-Narrow-Band-Gap Polymers.

Conjugated polymers with narrow band gaps are particularly useful for sorting and discriminating semiconducting single-walled carbon nanotubes (s-SWCNT) due to the low charge carrier injection barrier for transport. In this paper, we report two newly synthesized narrow-band-gap conjugated polymers (PNDITEG-TVT and PNDIC8TEG-TVT) based on naphthalene diimide (NDI) and thienylennevinylene (TVT) building blocks, decorated with different polar side chains that can be used for dispersing and discriminating s-SWCNT. Compared with the mid-band-gap conjugated polymer PNDITEG-AH, which is composed of naphthalene diimide (NDI) and head-to-head bithiophene building blocks, the addition of a vinylene linker eliminates the steric congestion present in head-to-head bithiophene, which promotes backbone planarity, extending the π-conjugation length and narrowing the band gap. Cyclic voltammetry (CV) and density functional theory (DFT) calculations suggest that inserting a vinylene group in a head-to-head bithiophene efficiently lifts the highest occupied molecular orbital (HOMO) level (−5.60 eV for PNDITEG-AH, −5.02 eV for PNDITEG-TVT, and −5.09 eV for PNDIC8TEG-TVT). All three polymers are able to select for s-SWCNT, as evidenced by the sharp transitions in the absorption spectra. Field-effect transistors (FETs) fabricated with the polymer:SWCNT inks display p-dominant properties, with higher hole mobilities when using the NDI-TVT polymers as compared with PNDITEG-AH (0.6 cm2 V–1 s–1 for HiPCO:PNDITEG-AH, 1.5 cm2 V–1 s–1 for HiPCO:PNDITEG-TVT, and 2.3 cm2 V–1 s–1 for HiPCO:PNDIC8TEG-TVT). This improvement is due to the better alignment of the HOMO level of PNDITEG-TVT and PNDIC8TEG-TVT with that of the dominant SWCNT specie.

Design of new hole transport materials based on triphenylamine derivatives using different π-linkers for the application in perovskite solar cells. A theoretical study.

New organic molecules containing five different compounds, commonly called p-linkers, located between the triphenylamine units, were theoretically designed and analyzed in order to be proposed as new hole transport materials (HTMs) in perovskite solar cells, in total ten new molecules were analyzed. The electronic, optical and hole transport properties were determined, similarly, the relationship of these properties with their molecular structure was also investigated by Density Functional Theory (DFT) and Density Functional Tight Binding (DFTB) calculations. Eight of the ten analyzed compounds exhibited the main absorption band out of the visible region; therefore these compounds did not present an overlap with the absorption spectra of the typical methylammonium lead iodide (MAPI) hybrid-perovskite. The results showed that the Highest occupied molecular orbital (HOMO) levels of the compounds are higher than the perovskite HOMO level, and in some cases these are even higher than the Spiro-OMeTAD HOMO. The calculated electronic couplings and the reorganization energy values provided useful information in order to determine if the systems were hole or electron transport materials.

Synthesis of innovative triphenylamine-functionalized organic photosensitizers outperformed the benchmark dye N719 for high-efficiency dye-sensitized solar cells

Herein, we present a thorough photovoltaic investigation of four triphenylamine organic sensitizers with D–π–A configurations and compare their photovoltaic performances to the conventional ruthenium-based sensitizer N719. SFA-5–8 are synthesized and utilized as sensitizers for dye-sensitized solar cell (DSSC) applications. The effects of the donor unit (triphenylamine), π-conjugation bridge (thiophene ring), and various acceptors (phenylacetonitrile and 2-cyanoacetamide derivatives) were investigated. Moreover, this was asserted by profound calculations of HOMO (highest occupied molecular orbital) and LUMO (lowest unoccupied molecular orbital) energy levels, the molecular electrostatic potential (MEP), and natural bond orbital (NBO) that had been studied for the TPA-sensitizers. Theoretical density functional theory (DFT) was performed to study the distribution of electron density between donor and acceptor moieties. The sensitization by the absorption of sensitizers SFA-5–8 leads to an obvious enhancement in the visible light absorption (300–750 nm) as well as a higher photovoltaic efficiency in the range of (5.53–7.56%). Under optimized conditions, SFA-7 showed outstanding sensitization of nanocrystalline TiO2, resulting in enhancing the visible light absorption and upgrading the power conversion efficiency (PCE) to approximately 7.56% over that reported for the N719 (7.29%). Remarkably, SFA-7 outperformed N719 by 4% in the total conversion efficiency. Significantly, the superior performance of SFA-7 could be mainly ascribed to the higher short-circuit photocurrents (Jsc) in parallel with larger open-circuit voltages (Voc) and more importantly, the presence of different anchoring moieties that could enhance the ability to fill the gaps on the surface of the TiO2 semiconductor. That could be largely reflected in the overall enhancement in the device efficiency. Moreover, the theoretical electronic and photovoltaic properties of all studied sensitizers have been compared with experimental results. All the 2-cyanoacrylamide derivative sensitizers demonstrated robust photovoltaic performance.

"Plug and Play" Photosensitizer-Catalyst Dyads for Water Oxidation.

We present a simple and easy-to-scale synthetic method to plug common organic photosensitizers into a cyanide-based network structure for the development of photosensitizer-water oxidation catalyst (PS-WOC) dyad assemblies for the photocatalytic water oxidation process. Three photosensitizers, one of which absorbs red light similar to P680 in photosystem II, were utilized to harvest different regions of the solar spectrum. Photosensitizers are covalently coordinated to CoFe Prussian blue structures to prepare PS-WOC dyads. All dyads exhibit steady water oxidation catalytic activities throughout a 6 h photocatalytic experiment. Our results demonstrate that the covalent coordination between the PS and WOC group not only enhances the photocatalytic activity but also improves the robustness of the organic PS group. The photocatalytic activity of “plug and play” dyads relies on several structural and electronic parameters, including the position of the energy levels of the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) of the PS with respect to the HOMO level of the catalytic site, the intensity and wavelength of the absorption band of the PS, and the number of catalytic sites.

Electronic and structural computing features of some chromene derivatives and evaluating their anticancer activities

Electronic and structural features of some of representative chromene derivatives were investigated in this work towards recognizing their anticancer roles. Density functional theory (DFT) calculations were performed to obtain five structures of chromene derivatives with the same skeleton of original structure. In addition to obtaining optimized structural geometries, electronic molecular orbital features were evaluated for the models. Energy levels of the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) indicated effects of additional R group pf chromene derivatives on electronic features. Based on such results, it was predicted that one of derivatives, L5, could better participate in interactions with other substances in comparison with other ligand structures. This achievement was obtained based on availability of HOMO and LUMO levels in lower energies easily catchable for electron transferring. On the other hand, L5 was assumed to interact in the weakest mode with other substances. Indeed, the main goal of this work was to examine anticancer activity of the investigated chromene derivatives, in which each of L1–L5 chromene derivatives were analyzed first to recognized electronic and structural features. Next, molecular docking (MD) simulations were performed to examine anticancer role of L1–L5 against methyltransferase cancerous enzyme target. The results indicated that formations of ligand-target complexes could be occurred within different types of interactions and surrounding amino acids of central ligand. In agreement with the achievements of analyses of single-standing L1–L5 compounds, L4-Target was seen as the strongest complex among possible complex formations. Moreover, values of binding energies and inhibition constant indicated that all five chromene derivatives could work as inhibitors of methyltransferase cancerous enzyme by the most advantage for L4 ligand. And as a final remark, details of such anticancer activity were recognized by graphical representations of ligand-target complexes showing types of interactions and involving amino acids in interactions.

Study of the Interaction Between Reduced Graphene Oxide and NO2Gas Molecules via Density Functional Theory (DFT)

Electronic properties such as density of state, energy gap, HOMO (the highest occupied molecular orbital) level, LUMO (the lowest unoccupied molecular orbital) level and density of bonds, as well as spectroscopic properties like infrared (IR), Raman scattering, force constant, and reduced masses for coronene C24, reduced graphene oxide (rGO) C24O5and interaction between C24O5and NO2gas molecules were investigated. Density functional theory (DFT) with the exchange hybrid function B3LYP with 6-311G** basis sets through the Gaussian 09 W software program was used to do these calculations. Gaussian view 05 was employed as a supplementary software to investigate the geometrical structure of C24, C24O5and the interaction of C24O5with NO2gas molecule. It shows the energy gap of coronene C243.5 eV because the effect of quantum confinement and the Coulomb interaction geometry greatly influence the quasi-particle band gap and C24Oxwhere x = 1–7 was from 0.89 eV to 1.6862 eV a function of number of oxygen atoms and compared with the experiment value of graphene oxide which was between 1 eV and 2.2 eV. The spectroscopic properties were compared with the experiment value of graphene, graphene oxide and NO2longitudinal optical (LO) modes of 1 585, 1 582 and 1 600 cm−1, respectively. The transition state of the interaction of rGO with nitrogen dioxide and Gibbs energy, enthalpy, activation entropy and reaction at various temperatures between 25°C and 100°C were calculated. The activation energy of C24O5with nitrogen dioxide decreases with increasing temperature.

Enhancing the Intermolecular Interactions of Ladder-Type Heteroheptacene-Based Nonfullerene Acceptors for Efficient Polymer Solar Cells by Incorporating Asymmetric Side Chains

Enhancing the Intermolecular Interactions of Ladder-Type Heteroheptacene-Based Nonfullerene Acceptors for Efficient Polymer Solar Cells by Incorporating Asymmetric Side Chains

Cost-Efficiency balanced polymer acceptors based on lowly fused Dithienopyrrolo[3, 2b]benzothiadiazole for 16.04% efficiency All-Polymer solar cells

All-polymer solar cells (All-PSCs) attracted increasing attention due to the outstanding thermal stability and mechanical properties. The current prevailing polymer acceptors for most efficient All-PSCs are polymerized high-performance small molecule acceptor of Y6, i.e. the dithienothiopheno[3,2-b]-pyrrolobenzothiadiazole (BTTP) based polymers. However, the BTTP-based polymers often show relatively shallow highest occupied molecular orbital (HOMO) energy level and high figure of merit (FOM), which limit the rational selection of paring donor polymers. Herein, we presented two low-cost polymer acceptors, namely as BTP-T2F and BTP-2T2F, based on lowly fused dithienopyrrolo[3,2b]benzothiadiazole (BTP, removing two thiophene cycles from BTTP). The BTP-based polymers exhibited deeper HOMO levels around −5.90 eV, which could match variable donor polymers with low-lying HOMO levels, such as low-cost PTQ10. Additionally, the synthesis was significantly simplified compared to BTTP-based polymers. A power conversion efficiency (PCE) of 14.32% was achieved in binary blend device containing PTQ10:BTP-2T2F. By adding a miscibility-enhancing PBDTCl-TPD as a third component, the top PCE of 16.04% was obtained in ternary blend All-PSCs. Combining the high device performance and low estimated cost, extraordinary cost-efficiency balance was realized within these BTP-based polymer acceptors.

Theoretical study of the influence of fluorination/chlorination on the electronic properties of donor:acceptor complexes

In this study, the electronic properties of J50:N2200 (benzodithiophene-alt-benzotriazole: NDI-bithiophene) interface before and after fluorination/chlorination were investigated based on the first-principles density functional theory (DFT). The results reveal that the donor (D) and acceptor (A) molecules exhibit direct band gap whether to be fluorinated/chlorinated or not, and the six D:A pairs constructed all display indirect band gap. Next, for the fluorinated/chlorinated D molecule J50, the slope of total density of states (TDOS) curve edge at the highest occupied molecular orbital (HOMO) energy level enlarges, indicating high electron locality; the fluorination/chlorination of the A molecule N2200 reduces the slope of the TDOS at the HOMO level, and the electron delocalization strengthens. Then, the difference ΔE1 of the lowest unoccupied molecular orbital (LUMO) levels between D and A, the difference ΔE2 of HOMO levels between D and A, and the difference ΔE3 between the HOMO level of the D and the LUMO level of the A were calculated about the D:A complexes. The consequences present that by using fluorine/chlorine (F/Cl) substitution at J50, ΔE1 and ΔE2 both decrease, and ΔE3 increases; for N2200, both ΔE1 and ΔE2 increase, and ΔE3 decreases. Since the higher open circuit voltage (V OC) is directly proportional to ΔE3, again ΔE1 and ΔE2 afford the driving force for charge transport, these expose that the fluorination/chlorination of J50 is beneficial to obtain the higher V OC, meanwhile, the F/Cl replacement in N2200 facilitates the separation of excitons. In addition, by the Bader charge analysis, the F/Cl substitution at D in D:A blends will promote the intramolecular charge transfer and enhance the molecular polarity; moreover, the substitution at A will improve the intermolecular charge transfer and the dipole electric field may be enhanced. Finally, the details also depend on the type of element and the position of substitution.

Elucidation of hole transport mechanism in efficient energy cascade organic photovoltaics using triple donor system

Recently, the energy cascade structure using multiple light-absorbing layers has been considered as a novel device architecture to overcome the inherent limitations of small-molecule organic photovoltaics (OPVs). The light-absorbing layers in the energy cascade OPVs should have a large overlap between the emission spectrum of a Förster resonance energy transfer (FRET) donor and absorption spectrum of a FRET acceptor. An equally important requirement is efficient charge transport across the organic layers by the formation of a suitable energy-level alignment. 5,10,15,20-tetraphenylbisbenz[5,6]indeno[1,2,3-cd:1′,2′,3′-lm]perylene (DBP)/5,6,11,12-tetraphenyltetracene (RUB)/5,12-diphenyltetracene (DPT) layers are representative donor systems, which exhibited a high power conversion efficiency in energy cascade OPVs. However, the detailed hole-transport mechanism has not been understood. In this study, the energy level alignment of C60/DBP/RUB/DPT/poly(3,4-ethylenedioxythiophene)-poly(styrene sulfonate) layers was investigated via in-situ ultraviolet photoelectron spectroscopy and inverse photoelectron spectroscopy. The highest-occupied molecular orbital levels of DBP/RUB/DPT were almost perfectly aligned after their contact, indicating an efficient hole transport toward the anode without hindrance of energy barrier after exciton dissociation. This is owing to the formation of an interface dipole that aligns the charge neutrality levels of the organic layers.