Showing papers by "Jianqi Zhang published in 2020"

Single-Junction Organic Photovoltaic Cells with Approaching 18% Efficiency.

Abstract: Optimizing the molecular structures of organic photovoltaic (OPV) materials is one of the most effective methods to boost power conversion efficiencies (PCEs). For an excellent molecular system with a certain conjugated skeleton, fine tuning the alky chains is of considerable significance to fully explore its photovoltaic potential. In this work, the optimization of alkyl chains is performed on a chlorinated nonfullerene acceptor (NFA) named BTP-4Cl-BO (a Y6 derivative) and very impressive photovoltaic parameters in OPV cells are obtained. To get more ordered intermolecular packing, the n-undecyl is shortened at the edge of BTP-eC11 to n-nonyl and n-heptyl. As a result, the NFAs of BTP-eC9 and BTP-eC7 are synthesized. The BTP-eC7 shows relatively poor solubility and thus limits its application in device fabrication. Fortunately, the BTP-eC9 possesses good solubility and, at the same time, enhanced electron transport property than BTP-eC11. Significantly, due to the simultaneously enhanced short-circuit current density and fill factor, the BTP-eC9-based single-junction OPV cells record a maximum PCE of 17.8% and get a certified value of 17.3%. These results demonstrate that minimizing the alkyl chains to get suitable solubility and enhanced intermolecular packing has a great potential in further improving its photovoltaic performance.

15.3% efficiency all-small-molecule organic solar cells enabled by symmetric phenyl substitution

Abstract: Synergistic optimization of donor-acceptor blend morphologyis a hurdle in the path of realizing efficient non-fullerene small-molecule organic solar cells (NFSM-OSCs) due to the anisotropic conjugated backbones of both donor and acceptor. Therefore, developing a facile molecular design strategy to effectively regulate the crystalline properties of photoactive materials, and thus, enable the optimization of blend morphology is of vital importance. In this study, a new donor molecule B1, comprising phenyl-substituted benzodithiophene (BDT) central unit, exhibits strong interaction with the non-fullerene acceptor BO-4Cl in comparison with its corresponding thiophene-substituted BDT-based material, BTR. As a result, the B1 is affected and induced from an edge-on to a face-on orientation by the acceptor, while the BTR and the acceptor behave individually for the similar molecular orientation in pristine and blend films according to grazing incidence wide angle X-ray scattering results. It means the donor-acceptor blend morphology is synergistically optimized in the B1 system, and the B1:BO-4Cl-based devices achieve an outstanding power conversion efficiency (PCE) of 15.3%, further certified to be 15.1% by the National Institute of Metrology, China. Our results demonstrate a simple and effective strategy to improve the crystalline properties of the donor molecule as well as synergistically optimize the morphology of the all-small-molecule system, leading to the high-performance NFSM-OSCs.

Synergistic Optimization Enables Large-Area Flexible Organic Solar Cells to Maintain over 98% PCE of the Small-Area Rigid Devices.

Abstract: Slot-die coating is generally regarded as the most effective large-scale methodology for the fabrication of organic solar cells (OSCs). However, the corresponding device performance significantly lags behind spin-coated devices. Herein, the active layer morphology, flexible substrate properties, and the processing temperature are optimized synergistically to obtain high power conversion efficiency (PCE) for both the flexible single cells and the modules. As a result, the 1 cm2 flexible devices produce an excellent PCE of 12.16% as compared to 12.37% for the spin-coated small-area (0.04 cm2 ) rigid devices. Likewise, for modules with an area of 25 cm2 , an extraordinary PCE of 10.09% is observed. Hence, efficiency losses associated with the upscaling are significantly reduced by the synergistic optimization. Moreover, after 1000 bending cycles at a bending radius of 10 mm, the flexible devices still produce over 99% of their initial PCE, whereas after being stored for over 6000 h in a glove box, the PCE reaches 103% of its initial value, indicating excellent device flexibility as well as superior shelf stability. These results, thus, are a promising confirmation the great potential for upscaling of large-area OSCs in the near future.

Ultratough graphene-black phosphorus films.

Abstract: Graphene-based films with high toughness have many promising applications, especially for flexible energy storage and portable electrical devices. Achieving such high-toughness films, however, remains a challenge. The conventional mechanisms for improving toughness are crack arrest or plastic deformation. Herein we demonstrate black phosphorus (BP) functionalized graphene films with record toughness by combining crack arrest and plastic deformation. The formation of covalent bonding P-O-C between BP and graphene oxide (GO) nanosheets not only reduces the voids of GO film but also improves the alignment degree of GO nanosheets, resulting in high compactness of the GO film. After further chemical reduction and π-π stacking interactions by conjugated molecules, the alignment degree of rGO nanosheets was further improved, and the voids in lamellar graphene film were also further reduced. Then, the compactness of the resultant graphene films and the alignment degree of reduced graphene oxide nanosheets are further improved. The toughness of the graphene film reaches as high as ∼51.8 MJ m-3, the highest recorded to date. In situ Raman spectra and molecular dynamics simulations reveal that the record toughness is due to synergistic interactions of lubrication of BP nanosheets, P-O-C covalent bonding, and π-π stacking interactions in the resultant graphene films. Our tough black phosphorus functionalized graphene films with high tensile strength and excellent conductivity also exhibit high ambient stability and electromagnetic shielding performance. Furthermore, a supercapacitor based on the tough films demonstrated high performance and remarkable flexibility.

Modulation of Donor Alkyl Terminal Chains with the Shifting Branching Point Leads to the Optimized Morphology and Efficient All-Small-Molecule Organic Solar Cells.

Abstract: Terminal group modification is one of the most influential factors for small-molecular donors compared with their polymer counterparts, resulting in an opportunity to optimize the morphology of all...

Long-term stable and highly efficient perovskite solar cells with a formamidinium chloride (FACl) additive

Abstract: Although the power conversion efficiency (PCE) of organometal halide perovskite solar cells (PSCs) has reached 25.2%, control of the crystallization process and its impact on film quality is still one of the main challenges. Here, a new perovskite growth method using formamidinium chloride (FACl) as an additive is introduced to enlarge the crystal grain size and improve the quality of the perovskite film. Strikingly, the champion power conversion efficiency of FA0.85MA0.15PbIxBr3−x-based and Cs0.05FA0.85MA0.10Pb(I0.97Br0.03)3-based PSC devices reaches 21.02% and 22.56%, respectively. The hysteresis index is found to decrease from 0.101 to 0.005, which is attributed to suppressed ion migration and surface charge trapping. Besides, the better film quality with FACl significantly increases the environmental stability of the perovskite films, yielding devices that maintain 90% of their initial efficiency after 1200 h under ambient air conditions, whereas the pristine devices without FACl only maintain 50% of their initial efficiency. Our solar cells processed with additives also achieve retardation of degradation of the PCE with a considerably enhanced environmental stability. This work offers a promising route through crystallization management to achieve high performance and stable PSCs.

Influence of Covalent and Noncovalent Backbone Rigidification Strategies on the Aggregation Structures of a Wide-Band-Gap Polymer for Photovoltaic Cells

Abstract: With the purpose of improving the backbone planarity and thus the charge transport property of the wide-band-gap ester-modified polymer, the covalent and noncovalent (F···S conformational lock) bac...

Surface controlled pseudo-capacitive reactions enabling ultra-fast charging and long-life organic lithium ion batteries

Abstract: To develop ultra-fast charging and long-life lithium ion batteries, a surface-controlled pseudo-capacitive reaction mechanism for high-performance organic lithium ion batteries is developed based on a coaxial nanocomposite of an active anthraquinone-based covalent organic framework (AQ-COF) and carbon nanotubes. AQ-COF was grown on the surface of carbon nanotubes (AQ-COF@CNTs) through in situ polymerization to improve the conductivity and to facilitate electrochemical properties. AQ-COF grown on CNTs exhibited excellent rate performance and was found to retain 76% of its initial capacity at a current density of 5000 mA g−1 (33C), and even retained 48% at an ultra-high current density of 10 000 mA g−1 (66.7C). Furthermore, under long term cycling performance investigations, the AQ-COF@CNT based cathode retained 100% of its initial capacity even after 3000 charge–discharge cycles. We further evaluated the charge storage mechanism and found that pseudocapacitance arising from surface-controlled redox reactions, coupled with excellent charge-transfer properties owing to the conductive CNT network and facilitated by the large surface area of active material, is mainly responsible for this excellent rate and cycling performance.

Non‐Preheating Processed Quasi‐2D Perovskites for Efficient and Stable Solar Cells

Abstract: Although the hot-casting (HC) technique is prevalent in developing preferred crystal orientation of quasi-2D perovskite films, the difficulty of accurately controlling the thermal homogeneity of substrate is unfavorable for the reproducibility of device fabrication. Herein, a facile and effective non-preheating (NP) film-casting method is proposed to realize highly oriented quasi-2D perovskite films by replacing the butylammonium (BA+ ) spacer partially with methylammonium (MA+ ) cation as (BA)2- x (MA)3+ x Pb4 I13 (x = 0, 0.2, 0.4, and 0.6). At the optimal x-value of 0.4, the resultant quasi-2D perovskite film possesses highly orientated crystals, associated with a dense morphology and uniform grain-size distribution. Consequently, the (BA)1.6 (MA)3.4 Pb4 I13 -based solar cells yield champion efficiencies of 15.44% with NP processing and 16.29% with HC processing, respectively. As expected, the HC-processed device shows a poor performance reproducibility compared with that of the NP film-casting method. Moreover, the unsealed device (x = 0.4) displays a better moisture stability with respect to the x = 0 stored in a 65% ± 5% relative humility chamber.

Control of Nanomorphology in Fullerene-Free Organic Solar Cells by Lewis Acid Doping with Enhanced Photovoltaic Efficiency.

Abstract: Generating desired efficiency enhancements in organic solar cells (OSCs) by charge-transfer doping requires to obtain modified optoelectronic properties while retaining the favorable nanomorphology...

Efficient Organic Solar Cells Based on Non-Fullerene Acceptors with Two Planar Thiophene-Fused Perylene Diimide Units.

Abstract: We designed and synthesized two non-fullerene acceptors (CDT-TFP and C8X-TFP), which comprise a central 4H-cyclopenta[2,1-b:3,4-b′]dithiophene (CDT) as the bridge and two thiophene-fused perylene d...

Red-emissive poly(phenylene vinylene)-derivated semiconductors with well-balanced ambipolar electrical transporting properties

Abstract: Herein, two new poly(phenylene vinylene)-derivated semiconductors, poly(benzopyrrolone-p-phenylene-vinylene) (PBPPV) and poly(benzopyrrolone-di-p-phenylene-vinylene) (diPBPPV), are designed and synthesized with lactam groups as the electron-deficient and lateral extending units and phenylethylene as the emissive element for achieving integrated optoelectronic properties. Comprehensive characterization demonstrates that both PBPPV and diPBPPV are red-emissive materials with a photoluminescent quantum yield (PLQY) of up to 7% and exhibit well-balanced ambipolar transport properties with the electron and hole mobility approaching 4.5 × 10−4 cm2 V−1 s−1 and 3.0 × 10−4 cm2 V−1 s−1, respectively. This work provides valuable guidelines for further improvement of integrated optoelectronic conjugated polymers by rational molecular design.

The post-treatment effects on open circuit voltages and device performances in a high efficiency all-small-molecule organic solar cell

Abstract: Post-treatment is a widely used approache to improve the device performance of all-small-molecule organic solar cells (ASM-OSCs), which leads to a balanced miscibility and crystallinity of the active layers. However, compared to as-cast devices, their efficiency is notably improved but normally accompanied with big open circuit voltage (Voc) loss after thermal annealing (TA) or solvent vapor annealing (SVA), which limits further breakthrough of the device performance and lacks investigation. In this manuscript, we design a novel molecule BSCl with a deep HOMO energy level and a good molecular assembling ability. Using IDIC-4Cl as an acceptor and combining TA and SVA, a PCE of 13.03% was achieved. The device improvements, film formation and Voc variations during the post-treatment methods were deeply investigated via Grazing incidence wide angle X-ray scattering and energy loss characterization. The characterization results illustrated that the decreased Voc during TA should be mainly due to the decreased ECT accompanied with a larger ΔVnon-rad, which is further ascribed to their upshifts in the HOMO energy levels. The Voc could be partly recovered after further SVA. Our results signify the importance of the shifts in the band-gap, ECT, and ultimately the energy levels during the post-treatment methods, providing useful guidance on high efficiency molecule optimization and a deep understanding on the energy loss investigation and film formation via device optimization.

Study of photovoltaic performances for asymmetrical and symmetrical chlorinated thiophene-bridge-based conjugated polymers

Abstract: Two conjugated donor polymers (PB2F-Cl and PB2F-2Cl) based on benzo[1,2-b:4,5-b′]dithiophene and benzo[1,2-c:4,5-c′]dithiophene-4,8-dione with asymmetrical and symmetrical chlorinated thiophene-bridges were designed and synthesized. Both polymers exhibited extremely deep HOMO levels of −5.50 and −5.56 eV for PB2F-Cl and PB2F-2Cl, respectively. Although PB2F-Cl had a more planar conjugated backbone, PB2F-Cl exhibited a weaker aggregation behaviour than PB2F-2Cl in chlorobenzene solution due to its regioirregular conjugated backbone. After blending with an IT-4F acceptor, the PB2F-Cl:IT-4F film exhibited a slightly stronger lamellar stacking and a weaker π stacking compared to the PB2F-2Cl:IT-4F film as confirmed by grazing-incidence wide-angle X-ray scattering (GIWAXS) measurements. In PSCs, the power conversion efficiency (PCE) of the PB2F-Cl:IT-4F-based PSC was 10.81%, while the PCE of the PB2F-2Cl:IT-4F-based PSC reached 12.79%.

Ideal alloys of two donor isomers with non-covalently conformational locking for ternary organic solar cells

Abstract: Ternary organic solar cells (OSCs) based on the alloy model have great potential in maximizing the improvement of device performance due to the probability of simultaneously enhancing the photocurrent through morphology optimization and improving open circuit voltage (Voc) by energy level adjustment. However, rationally designing compatible materials and constructing an effective alloy remain difficult. In this manuscript, two donor isomers, BT-TO-ID and BT-OT-ID with non-covalently conformational locking of alkoxy groups at different position, were designed and synthesized to obtain an “ideal alloy”. A linearly tunable Voc was observed between the Voc limitation of binary blends with the changes of the composition across the full range, indicating the behavior of an ideal alloy in the ternary blends. A face-on molecular packing and an appropriate phase separation was observed in the ternary blends due to the strong interactions between the two isomers, which facilitated charge transport and charge recombination suppression. Notable improvements of 76% and 29% in device performance were obtained for the ternary blends compared with BT-OT-ID based and BT-OT-ID based binary devices, respectively. Therefore, this work provided a probable molecular design strategy to guide the construction of an effective alloy in ternary OSCs.

Enhanced photovoltaic effect from naphtho[2,3-c]thiophene-4,9-dione-based polymers through alkyl side chain induced backbone distortion

Abstract: The innovation of photoactive layer materials is crucial for improving the power conversion efficiency (PCE) of polymer solar cells (PSCs) Herein, we report two polymer donors (PBTN-o and PBTN-p), which only differ in alkyl chains substituted at sites (6,7- or 5,8-) of the naphtho[2,3-c]thiophene-4,9-dione (NTD) unit The single crystals of both NTD monomers demonstrate that NTD with alkyl chains at the 6,7-sites has a planar NTD skeleton, and surprisingly, NTD with alkyl chains at the 5,8-sites produces a bent NTD skeleton The bent NTD-based polymer (PBTN-p) exhibits a more twisted conjugated backbone than PBTN-o Our comparative studies show that PBTN-p possesses suitable aggregation properties that can optimize the photoactive layer morphology in NF PSCs In PSCs, the optimal PBTN-o:BO-4Cl-based device shows a PCE of 1185% with a VOC of 084 V, JSC of 2241 mA cm−2, and FF of 063 In contrast, the optimal PBTN-p:BO-4Cl-based device exhibits a better PCE of 1410% with the same VOC of 084 V, and an enhanced JSC of 2467 mA cm−2 and FF of 068 This work provides a new insight into BHJ morphology optimization by side chain induced polymer main chain twisting in PSCs

The interfacial degradation mechanism of polymer:fullerene bis-adduct solar cells and their stability improvement

Abstract: Although fullerene bis-adducts have been widely used in polymer solar cells for their high LUMO energy level and good performance, the degradation behavior of this class of solar cells has not been well understood. In this paper, the performance and stability of the solar cells based on P3HT:fullerene bis-adducts, including bis-PC61BM and ICBA, were systematically investigated. Different from the P3HT:PC61BM cell, these bis-adduct based cells showed fast open circuit (VOC) and fill factor (FF) decays. The partial recovery of VOC and FF of the aged cells by renewing the MoO3/Al electrode indicated that degradation at the photoactive layer and MoO3 interface is the main reason for VOC and FF decays. The X-ray photoelectronic spectroscopy analysis confirmed that under light illumination, Mo6+ of MoO3 is partially reduced to Mo5+. By inserting a thin layer of C60, both MoO3 reduction and performance decays are slowed down, confirming that photoreduction of MoO3 by P3HT is the degradation mechanism for P3HT:bis-PC61BM cells. Finally, we found that doping a polymer:fullerene bis-adduct layer with piperazine increases the fullerene content on the surface of the photoactive layer, which consequently lowers the reduction of Mo6+ and improves the stability of the solar cells. This work gives a detailed understanding of the interfacial degradation of PSCs and provides effective solutions, which has important guiding significance for improving the stability of different types of polymer solar cells.