Inner Side Chain Modification of Small Molecule Acceptors Enables Lower Energy Loss and High Efficiency of Organic Solar Cells Processed with Non-halogenated Solvents.

Organic solar cells (OSCs) processed with non-halogenated solvents usually suffer from excessive self-aggregation of small molecule acceptors (SMAs), severe phase separation and higher energy loss (E), leading to reduced open-circuit voltage (V) and power conversion efficiency (PCE). Regulating the intermolecular interaction to disperse the aggregation and further improve the molecular packing order of SMAs would be an effective strategy to solve this problem. Here, we designed and synthesized two SMAs L8-PhF and L8-PhMe by introducing different substituents (fluorine for L8-PhF and methyl for L8-PhMe) on the phenyl end group of the inner side chains of L8-Ph, and investigated the effect of the substituents on the intermolecular interaction of SMAs, E and performance of OSCs processed with non-halogenated solvents.

High-Performance Intrinsically Stretchable Organic Photovoltaics Enabled by Robust Silver Nanowires/S-PH1000 Hybrid Transparent Electrodes.

Intrinsically stretchable organic photovoltaics (is-OPVs) hold significant promise for integration into self-powered wearable electronics. However, their potential is hindered by the lack of sufficient consistency between optoelectronic and mechanical properties. This is primarily due to the limited availability of stretchable transparent electrodes (STEs) that possess both high conductivity and stretchability.

Halogenated Dibenzo[f,h]quinoxaline Units Constructed 2D-Conjugated Guest Acceptors for 19% Efficiency Organic Solar Cells.

Halogenation of Y-series small-molecule acceptors (Y-SMAs) is identified as an effective strategy to optimize photoelectric properties for achieving improved power-conversion-efficiencies (PCEs) in binary organic solar cells (OSCs). However, the effect of different halogenation in the 2D-structured large π-fused core of guest Y-SMAs on ternary OSCs has not yet been systematically studied. Herein, four 2D-conjugated Y-SMAs (X-QTP-4F, including halogen-free H-QTP-4F, chlorinated Cl-QTP-4F, brominated Br-QTP-4F, and iodinated I-QTP-4F) by attaching different halogens into 2D-conjugation extended dibenzo[f,h]quinoxaline core are developed.

High Performance As-Cast Organic Solar Cells Enabled by a Refined Double-Fibril Network Morphology and Improved Dielectric Constant of Active Layer.

High performance organic solar cells (OSCs) are usually realized by using post-treatment and/or additive, which can induce the formation of metastable morphology, leading to unfavorable device stability. In terms of the industrial production, the development of high efficiency as-cast OSCs is crucially important, but it remains a great challenge to obtain appropriate active layer morphology and high power conversion efficiency (PCE). Here, efficient as-cast OSCs are constructed via introducing a new polymer acceptor PY-TPT with a high dielectric constant into the D18:L8-BO blend to form a double-fibril network morphology.

On the role of asymmetric molecular geometry in high-performance organic solar cells.

Although asymmetric molecular design has been widely demonstrated effective for organic photovoltaics (OPVs), the correlation between asymmetric molecular geometry and their optoelectronic properties is still unclear. To access this issue, we have designed and synthesized several symmetric-asymmetric non-fullerene acceptors (NFAs) pairs with identical physical and optoelectronic properties. Interestingly, we found that the asymmetric NFAs universally exhibited increased open-circuit voltage compared to their symmetric counterparts, due to the reduced non-radiative charge recombination.

High-efficiency flexible organic solar cells with a polymer-incorporated pseudo-planar heterojunction.

Organic solar cells (OSCs) are considered as a crucial energy source for flexible and wearable electronics. Pseudo-planar heterojunction (PPHJ) OSCs simplify the solution preparation and morphology control. However, non-halogenated solvent-printed PPHJ often have an undesirable vertical component distribution and insufficient donor/acceptor interfaces.

Green-Solvent Processed Blade-Coating Organic Solar Cells with an Efficiency Approaching 19% Enabled by Alkyl-Tailored Acceptors.

Power-conversion-efficiencies (PCEs) of organic solar cells (OSCs) in laboratory, normally processed by spin-coating technology with toxic halogenated solvents, have reached over 19%. However, there is usually a marked PCE drop when the blade-coating and/or green-solvents toward large-scale printing are used instead, which hampers the practical development of OSCs. Here, a new series of N-alkyl-tailored small molecule acceptors named YR-SeNF with a same molecular main backbone are developed by combining selenium-fused central-core and naphthalene-fused end-group.

Nonhalogenated Dual-Slot-Die Processing Enables High-Efficiency Organic Solar Cells.

Organic solar cells (OSCs) are promising candidates for next-generation photovoltaic technologies, with their power conversion efficiencies (PCEs) reaching 19%. However, the typically used spin-coating method, toxic halogenated processing solvents, and the conventional bulk-heterojunction (BHJ), which causes excessive charge recombination, hamper the commercialization and further efficiency promotion of OSCs. Here, a simple but effective dual-slot-die sequential processing (DSDS) strategy is proposed to address the above issues by achieving a continuous solution supply, avoiding the solubility limit of the nonhalogen solvents, and creating a graded-BHJ morphology.

Molecular-Shape-Controlled Nonfused Ring Electron Acceptors for High-Performance Organic Solar Cells with Tunable Phase Morphology.

Two nonfused ring electron acceptors (NFREAs), BTh-OC8-2F and DTh-OC8-2F, with different molecular shapes are designed and synthesized. Both acceptors can form planar molecular shapes by the assistance of S···O intramolecular interactions. Differently, BTh-OC8-2F, with a linear molecular backbone and two trans-arranged side chains at the core unit, exhibits much stronger crystallinity than DTh-OC8-2, with a C-shape molecular shape and two cis-arranged steric side chains at the core unit.

Unraveling the Photovoltaic, Mechanical, and Microstructural Properties and Their Correlations in Simple Poly(3-pentylthiophene) Solar Cells.

The power conversion efficiency of polythiophene organic solar cells is constantly refreshed. Despite the renewed device efficiency, very few efforts have been devoted to understanding how the type of electron acceptor alters the photovoltaic and mechanical properties of these low-cost solar cells. Herein, the authors conduct a thorough investigation of photovoltaic and mechanical characteristics of a simple yet less-explored polythiophene, namely poly(3-pentylthiophene) (P3PT), in three different types of organic solar cells, where ZY-4Cl, PC BM, and N2200 are employed as three representative acceptors, respectively.

Reducing Energy Disorder in Perovskite Solar Cells by Chelation.

In inverted perovskite solar cells (PSCs), the fullerene derivative [6,6]-phenyl-C-butyric acid methyl ester (PCBM) is a widely used electron transport material. However, a high degree of energy disorder and inadequate passivation of PCBM limit the efficiency of devices, and severe self-aggregation and unstable morphology limit the lifespan of devices. Here, we design a series of fullerene dyads FP-C ( = 4, 8, 12) to replace PCBM as an electron transport layer, where [60]fullerene is linked with a terpyridine chelating group via a flexible alkyl chain of different lengths as a spacer.

Strengthening the Intermolecular Interaction of Prototypical Semicrystalline Conjugated Polymer Enables Improved Photocurrent Generation at the Heterojunction.

The intra and intermolecular interactions (J- and H-type aggregation) in the conjugated polymer films are found to readily facilitate the electron and hole transport, respectively. However, how those different aggregation types influence the photocurrent generation at the heterojunction is still mysterious, especially for the newly developed semicrystalline conjugated polymers. Here, the prototypical copolymer PM6 is used to tune the relative content of aggregation types with various halogen-free processing solvents.

Different Morphology Dependence for Efficient Indoor Organic Photovoltaics: The Role of the Leakage Current and Recombination Losses.

Efficient indoor organic photovoltaics (OPVs) have attracted strong attention for their application in indoor electronic devices. However, the route to optimal photoactive film morphology toward high-performance indoor devices has remained obscure. The leakage current dominated by morphology exerts distinguishing influence on the performance under different illuminations.

Intermolecular Interaction Control Enables Co-optimization of Efficiency, Deformability, Mechanical and Thermal Stability of Stretchable Organic Solar Cells.

Promoting efficiency, deformability, and life expectancy of stretchable organic solar cells (OSCs) have always been key concerns that researchers are committed to solving. However, how to improve them simultaneously remains challenging, as morphology parameters, such as ordered molecular arrangement, beneficial for highly efficient devices actually limits mechanical stability and deformability. In this study, the unfavorable trade-off among these properties has been reconciled in an all-polymer model system utilizing a mechanically deformable guest component.

Efficient Ternary Organic Solar Cells with a New Electron Acceptor Based on 3,4-(2,2-Dihexylpropylenedioxy)thiophene.

In this work, a ternary blend strategy based on PBDB-T and two small molecular acceptors (IDTT-OB and ) is demonstrated to simultaneously improve the photocurrent and reduce the voltage loss in organic solar cells (OSCs). The improved photocurrent is partially due to a broad absorption spectrum of the active layer. In addition, we find that the ternary system possesses a higher degree of crystallinity, smaller domain size, higher domain purity, and higher and more balanced charge-carrier mobilities in comparison with the two corresponding binary systems.

Noncovalently fused-ring electron acceptors with near-infrared absorption for high-performance organic solar cells.

Non-fullerene fused-ring electron acceptors boost the power conversion efficiency of organic solar cells, but they suffer from high synthetic cost and low yield. Here, we show a series of low-cost noncovalently fused-ring electron acceptors, which consist of a ladder-like core locked by noncovalent sulfur-oxygen interactions and flanked by two dicyanoindanone electron-withdrawing groups. Compared with that of similar but unfused acceptor, the presence of ladder-like structure markedly broadens the absorption to the near-infrared region.

Single-Junction Polymer Solar Cells with 16.35% Efficiency Enabled by a Platinum(II) Complexation Strategy.

A new strategy of platinum(II) complexation is developed to regulate the crystallinity and molecular packing of polynitrogen heterocyclic polymers, optimize the morphology of the active blends, and improve the efficiency of the resulting nonfullerene polymer solar cells (NF-PSCs). The newly designed s-tetrazine (s-TZ)-containing copolymer of PSFTZ (4,8-bis(5-((2-butyloctyl)thio)-4-fluorothiophen-2-yl)benzo[1,2-b:4,5-b']dithiophene-alt-3,6-bis(4-octylthiophen-2-yl)-1,2,4,5-tetrazine) has a strong aggregation property, which results in serious phase separation and large domains when blending with Y6 ((2,2'-((2Z,2'Z)-((12,13-bis(2-ethylhexyl)-3,9-diundecyl-12,13-dihydro-[1,2,5]thiadiazolo[3,4-e]thieno[2″,3″:4',5']thieno[2',3':4,5]pyrrolo[3,2-g]thieno[2',3':4,5]thieno[3,2-b]indole-2,10-diyl)bis(methanylylidene))bis(5,6-difluoro-3-oxo-2,3-dihydro-1H-indene-2,1-diylidene))dimalononitrile)), and produces a power-conversion efficiency (PCE) of 13.03%.

Fine Optimization of Morphology Evolution Kinetics with Binary Additives for Efficient Non-Fullerene Organic Solar Cells.

The power conversion efficiency of polymer solar cells (PSCs) is strongly affected by active layer morphology. Here, two solvent additives (ODT: octance-1,8-dithiol; DIO: 1,8-diiodooctane) are used to optimize the bulk heterojunction morphology of FTAZ:ITIC-Th based PSCs and ≈11% efficiency is obtained, which is 10% higher than the untreated device. Based on the morphological characterizations, the influence of binary solvent additives on manipulating molecular packing and phase separation of blend films is successfully revealed.

Low-Energy-Loss Polymer Solar Cells with 14.52% Efficiency Enabled by Wide-Band-Gap Copolymers.

Two wide band-gap copolymers poly[4,8-bis(5-(2-butylhexylthio)thiophen-2-yl)benzo[1,2-b:4,5-b']dithiophene-2,6-diyl-alt-TZNT] (PBDTS-TZNT) and poly[4,8-bis(4-fluoro-5-(2-butylhexylthio)thiophen-2-yl)benzo[1,2-b:4,5-b']dithiophene-2,6-diyl-alt-TZNT] (PBDTSF-TZNT) based on naphtho[1,2-c:5,6-c]bis(2-octyl-[1,2,3]triazole) (TZNT) and benzo[1,2-b:4,5-b']dithiophene (BDT) with different conjugated side chains have been developed for efficient nonfullerene polymer solar cells (NF-PSCs). The rigid planar backbone of BDT and TZNT units imparted high crystallinity and good molecular stacking property to these copolymers. Using 3,9-bis(2-methylene-(3-(1,1-dicyanomethylene)-indanone)-5,5,11,11-tetrakis(4-hexylphenyl)-dithieno[2,3-d:2',3'-d']-s-indaceno[1,2-b:5,6-b']-dithiophene (ITIC) as the acceptor, PBDTSF-TZNT devices showed a high V of 0.

Controlling Molecular Packing and Orientation via Constructing a Ladder-Type Electron Acceptor with Asymmetric Substituents for Thick-Film Nonfullerene Solar Cells.

A nonfullerene acceptor, IDTT-OB, employing indacenodithieno[3,2- b]thiophene (IDTT) decorated with asymmetric substituents as the core, is designedly prepared. In comparison with the analogue IDT-OB, extending the five-heterocyclic indacenodithiophene (IDT) core to seven-heterocyclic fused ring endows IDTT-OB with more broad absorption and elevated highest occupied molecular orbital energy level. In addition, IDTT-OB shows a more intense molecular packing and a higher crystalline behavior with a strong face-on orientation in the neat film and the PBDB-T:IDTT-OB blend film.

Dithienothiapyran: An Excellent Donor Block for Building High-Performance Copolymers in Nonfullerene Polymer Solar Cells.

In this work, a new but excellent donor block dithienothiapyran (DTTP) was developed for constructing highly efficient wide band gap copolymer donors. Compared to dithienopyran (DTP), DTTP features weaken electron-donating ability and more planar-conjugated backbones. Polymer-fluorinated benzotriazole (FBTA) based on DTTP exhibits lower highest occupied molecular orbital level (-5.

Achieving Balanced Crystallinity of Donor and Acceptor by Combining Blade-Coating and Ternary Strategies in Organic Solar Cells.

As a prototype tool for slot-die coating, blade-coating exhibits excellent compatibility with large-area roll-to-roll coating. A ternary organic solar cell based on PBDB-T:PTB7-Th:FOIC blends is fabricated by blade-coating and exhibits a power conversion efficiency of 12.02%, which is one of the highest values for the printed organic solar cells in ambient environment.

Highly Efficient Nonfullerene Polymer Solar Cells Enabled by a Copper(I) Coordination Strategy Employing a 1,3,4-Oxadiazole-Containing Wide-Bandgap Copolymer Donor.

A novel wide-bandgap copolymer of PBDT-ODZ based on benzo[1,2-b:4,5-b' ]dithiophene (BDT) and 1,3,4-oxadiazole (ODZ) blocks is developed for efficient nonfullerene polymer solar cells (NF-PSCs). PBDT-ODZ exhibits a wide bandgap of 2.12 eV and a low-lying highest occupied molecular orbital (HOMO) level of -5.

Realizing Over 13% Efficiency in Green-Solvent-Processed Nonfullerene Organic Solar Cells Enabled by 1,3,4-Thiadiazole-Based Wide-Bandgap Copolymers.

Two novel wide-bandgap copolymers, PBDT-TDZ and PBDTS-TDZ, are developed based on 1,3,4-thiadiazole (TDZ) and benzo[1,2-b:4,5-b']dithiophene (BDT) building blocks. These copolymers exhibit wide bandgaps over 2.07 eV and low-lying highest occupied molecular orbital (HOMO) levels below -5.

Highly Efficient Ternary-Blend Polymer Solar Cells Enabled by a Nonfullerene Acceptor and Two Polymer Donors with a Broad Composition Tolerance.

In this work, highly efficient ternary-blend organic solar cells (TB-OSCs) are reported based on a low-bandgap copolymer of PTB7-Th, a medium-bandgap copolymer of PBDB-T, and a wide-bandgap small molecule of SFBRCN. The ternary-blend layer exhibits a good complementary absorption in the range of 300-800 nm, in which PTB7-Th and PBDB-T have excellent miscibility with each other and a desirable phase separation with SFBRCN. In such devices, there exist multiple energy transfer pathways from PBDB-T to PTB7-Th, and from SFBRCN to the above two polymer donors.