Isomerization Engineering of Solid Additives Enables Highly Efficient Organic Solar Cells via Manipulating Molecular Stacking and Aggregation of Active Layer.

Morphology control is crucial in achieving high-performance organic solar cells (OSCs) and remains a major challenge in the field of OSC. Solid additive is an effective strategy to fine-tune morphology, however, the mechanism underlying isomeric solid additives on blend morphology and OSC performance is still vague and urgently requires further investigation. Herein, two solid additives based on pyridazine or pyrimidine as core units, M1 and M2, are designed and synthesized to explore working mechanism of the isomeric solid additives in OSCs. The smaller steric hindrance and larger dipole moment facilitate better π-π stacking and aggregation in M1-based active layer. The M1-treated all-small-molecule OSCs (ASM OSCs) obtain an impressive efficiency of 17.57%, ranking among the highest values for binary ASM OSCs, with 16.70% for M2-treated counterparts. Moreover, it is imperative to investigate whether the isomerization engineering of solid additives works in state-of-the-art polymer OSCs. M1-treated D18-Cl:PM6:L8-BO-based devices achieve an exceptional efficiency of 19.70% (certified as 19.34%), among the highest values for OSCs. The work provides deep insights into the design of solid additives and clarifies the potential working mechanism for optimizing the morphology and device performance through isomerization engineering of solid additives.

Amino-Functionalized Graphdiyne Derivative as a Cathode Interface Layer with High Thickness Tolerance for Highly Efficient Organic Solar Cells.

Efficient cathode interfacial materials (CIMs) are essential components for effectively enhancing the performance of organic solar cells (OSCs). Although high-performance CIMs are desired to meet the requirements of various OSCs, potential candidates for CIMs are scarce. Herein, an amino-functionalized graphdiyne derivative (GDY-N) is developed, which represents the first example of GDY that exhibits favorable solubility in alcohol. Utilizing GDY-N as the CIM, an outstanding champion PCE of 19.30% for devices based on the D18-Cl:L8-BO (certified result: 19.05%) is achieved, which is among the highest efficiencies reported to date in OSCs. Remarkably, the devices based on GDY-N exhibit a thickness-insensitive characteristic, maintaining 95% of their initial efficiency even with a film thickness of 25 nm. Moreover, the GDY-N displays wide universality and facilitates exceptional stability in OSCs. This work not only enriches the diversity of GDY derivatives, but also demonstrates the feasibility of GDY derivatives as CIMs with high thickness tolerance in OSCs.

Simultaneously Enhanced Efficiency and Mechanical Durability in Ternary Solar Cells Enabled by Low-Cost Incompletely Separated Fullerenes.

All-polymer solar cells (all-PSCs) are one of the most promising application-oriented organic photovoltaic technologies due to their excellent operational and mechanical stability. However, the power conversion efficiencies (PCEs) are mostly lower than 16%, restricting their core competitiveness. Furthermore, the improvement of mechanical durability is rarely paid attention to cutting-edge all-PSCs. This work deploys a low-cost "technical grade" PCBM (incompletely separated but pure mixtures containing ≥90% [70]PCBM or [60]PCBM), into the efficient PM6:PY-IT all-polymer blend, successfully yielding a high-performance ternary device with 16.16% PCE, among the highest PCE values for all-PSCs. Meanwhile, an excellent mechanical property (i.e., crack onset strain = 11.1%) promoted from 9.5% for the ternary system is also demonstrated. The "technical grade" PCBM slightly disrupts the crystallization of polymers, and disperses well into the amorphous polymer regions of the all-PSC blends, thus facilitating charge transport and improving film ductility simultaneously. All these results confirm introducing low-cost "technical grade" PCBM with high electron mobility into all-polymer blends can improve carrier mobility, reduce charge recombination, and optimize morphology of the amorphous polymer regions, thus yielding more efficient and mechanically durable all-PSCs.

The coupling and competition of crystallization and phase separation, correlating thermodynamics and kinetics in OPV morphology and performances.

The active layer morphology transition of organic photovoltaics under non-equilibrium conditions are of vital importance in determining the device power conversion efficiency and stability; however, a general and unified picture on this issue has not been well addressed. Using combined in situ and ex situ morphology characterizations, morphological parameters relating to kinetics and thermodynamics of morphology evolution are extracted and studied in model systems under thermal annealing. The coupling and competition of crystallization and demixing are found to be critical in morphology evolution, phase purification and interfacial orientation. A unified model summarizing different phase diagrams and all possible kinetic routes is proposed. The current observations address the fundamental issues underlying the formation of the complex multi-length scale morphology in bulk heterojunction blends and provide useful morphology optimization guidelines for processing devices with higher efficiency and stability.

Low-Bandgap Porphyrins for Highly Efficient Organic Solar Cells: Materials, Morphology, and Applications.

With developments in materials, thin-film processing, fine-tuning of morphology, and optimization of device fabrication, the performance of organic solar cells (OSCs) has improved markedly in recent years. Designing low-bandgap materials has been a focus in order to maximize solar energy conversion. However, there are only a few successful low-bandgap donor materials developed with near-infrared (NIR) absorption that are well matched to the existing efficient acceptors. Porphyrin has shown great potential as a useful building block for constructing low-bandgap donor materials due to its large conjugated plane and strong absorption. Porphyrin-based donor materials have been shown to contribute to many record-high device efficiencies in small molecule, tandem, ternary, flexible, and OSC/perovskite hybrid solar cells. Specifically, non-fullerene small-molecule solar cells have recently shown a high power conversion efficiency of 12% using low-bandgap porphyrin. All these have validated the great potential of porphyrin derivatives as effective donor materials and made DPPEZnP-TRs a family of best low-bandgap donor materials in the OSC field so far. Here, recent progress in the rational design, morphology, dynamics, and multi-functional applications starting from 2015 will be highlighted to deepen understanding of the structure-property relationship. Finally, some future directions of porphyrin-based OSCs are presented.

Graphdiyne Derivative as Multifunctional Solid Additive in Binary Organic Solar Cells with 17.3% Efficiency and High Reproductivity.

Morphology tuning of the blend film in organic solar cells (OSCs) is a key approach to improve device efficiencies. Among various strategies, solid additive is proposed as a simple and new way to enable morphology tuning. However, there exist few solid additives reported to meet such expectations. Herein, chlorine-functionalized graphdiyne (GCl) is successfully applied as a multifunctional solid additive to fine-tune the morphology and improve device efficiency as well as reproductivity for the first time. Compared with 15.6% efficiency for control devices, a record high efficiency of 17.3% with the certified one of 17.1% is obtained along with the simultaneous increase of short-circuit current (Jsc ) and fill factor (FF), displaying the state-of-the-art binary organic solar cells at present. The redshift of the film absorption, enhanced crystallinity, prominent phase separation, improved mobility, and decreased charge recombination synergistically account for the increase of Jsc and FF after introducing GCl into the blend film. Moreover, the addition of GCl dramatically reduces batch-to-batch variations benefiting mass production owing to the nonvolatile property of GCl. All these results confirm the efficacy of GCl to enhance device performance, demonstrating a promising application of GCl as a multifunctional solid additive in the field of OSCs.

Over 12% Efficiency Nonfullerene All-Small-Molecule Organic Solar Cells with Sequentially Evolved Multilength Scale Morphologies.

In this paper, two near-infrared absorbing molecules are successfully incorporated into nonfullerene-based small-molecule organic solar cells (NFSM-OSCs) to achieve a very high power conversion efficiency (PCE) of 12.08%. This is achieved by tuning the sequentially evolved crystalline morphology through combined solvent additive and solvent vapor annealing, which mainly work on ZnP-TBO and 6TIC, respectively. It not only helps improve the crystallinity of the ZnP-TBO and 6TIC blend, but also forms multilength scale morphology to enhance charge mobility and charge extraction. Moreover, it simultaneously reduces the nongeminate recombination by effective charge delocalization. The resultant device performance shows remarkably enhanced fill factor and Jsc . These result in a very respectable PCE, which is the highest among all NFSM-OSCs and all small-molecule binary solar cells reported so far.

Highly Efficient Porphyrin-Based OPV/Perovskite Hybrid Solar Cells with Extended Photoresponse and High Fill Factor.

Employing a layer of bulk-heterojunction (BHJ) organic semiconductors on top of perovskite to further extend its photoresponse is considered as a simple and promising way to enhance the efficiency of perovskite-based solar cells, instead of using tandem devices or near infrared (NIR)-absorbing Sn-containing perovskites. However, the progress made from this approach is quite limited because very few such hybrid solar cells can simultaneously show high short-circuit current (JSC ) and fill factor (FF). To find an appropriate NIR-absorbing BHJ is essential for highly efficient, organic, photovoltaics (OPV)/perovskite hybrid solar cells. The materials involved in the BHJ layer not only need to have broad photoresponse to increase JSC , but also possess suitable energy levels and high mobility to afford high VOC and FF. In this work, a new porphyrin is synthesized and blended with [6,6]-phenyl-C61-butyric acid methyl ester (PCBM) to function as an efficient BHJ for OPV/perovskite hybrid solar cells. The extended photoresponse, well-matched energy levels, and high hole mobility from optimized BHJ morphology afford a very high power conversion efficiency (PCE) (19.02%) with high Voc , JSC , and FF achieved simultaneously. This is the highest value reported so far for such hybrid devices, which demonstrates the feasibility of further improving the efficiency of perovskite devices.

11% Efficient Ternary Organic Solar Cells with High Composition Tolerance via Integrated Near-IR Sensitization and Interface Engineering.

Highly efficient electron extraction is achieved by using a photoconductive cathode interlayer in inverted ternary organic solar cells (OSCs) where a near-IR absorbing porphyrin molecule is used as the sensitizer. The OSCs show improved device performance when the ratio of the two donors varies in a large region and a maximum power conversion efficiency up to 11.03% is demonstrated.

Multi-Length-Scale Morphologies Driven by Mixed Additives in Porphyrin-Based Organic Photovoltaics.

A new category of deep-absorbing small molecules is developed. Optimized devices driven by mixed additives show a remarkable short-circuit current of ≈20 mA cm(-2) and a highest power conversion efficiency of 9.06%. A multi-length-scale morphology is formed, which is fully characterized by resonant soft X-ray scattering, high-angle annular dark film image transmission electron microscopy, etc.

Hydrophilic Conjugated Polymers with Large Bandgaps and Deep-Lying HOMO Levels as an Efficient Cathode Interlayer in Inverted Polymer Solar Cells.

Two hydrophilic conjugated polymers, PmP-NOH and PmP36F-NOH, with polar diethanol-amine on the side chains and main chain structures of poly(meta-phenylene) and poly(meta-phenylene-alt-3,6-fluorene), respectively, are successfully synthesized. The films of PmP-NOH and PmP36F-NOH show absorption edges at 340 and 343 nm, respectively. The calculated optical bandgaps of the two polymers are 3.65 and 3.62 eV, respectively, the largest ones so far reported for hydrophilic conjugated polymers. PmP-NOH and PmP36F-NOH also possess deep-lying highest occupied molecular orbital levels of -6.19 and -6.15 eV, respectively. Inserting PmP-NOH and PmP36F-NOH as a cathode interlayer in inverted polymer solar cells with a PTB7/PC71 BM blend as the active layer, high power conversion efficiencies of 8.58% and 8.33%, respectively, are achieved, demonstrating that the two hydrophilic polymers are excellent interlayers for efficient inverted polymer solar cells.