Although the field of polymer solar cell has seen much progress in device performance in the past few years, several limitations are holding back its further development For instance, current high-efficiency (>90%) cells are restricted to material combinations that are based on limited donor polymers and only one specific fullerene acceptor Here we report the achievement of high-performance (efficiencies up to 108%, fill factors up to 77%) thick-film polymer solar cells for multiple polymer:fullerene combinations via the formation of a near-ideal polymer:fullerene morphology that contains highly crystalline yet reasonably small polymer domains This morphology is controlled by the temperature-dependent aggregation behaviour of the donor polymers and is insensitive to the choice of fullerenes The uncovered aggregation and design rules yield three high-efficiency (>10%) donor polymers and will allow further synthetic advances and matching of both the polymer and fullerene materials, potentially leading to significantly improved performance and increased design flexibility

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Aggregation and morphology control enables multiple cases of high-efficiency polymer solar cells.

A nonfullerene-based polymer solar cell (PSC) that significantly outperforms fullerene-based PSCs with respect to the power-conversion efficiency is demonstrated for the first time. An efficiency of >11%, which is among the top values in the PSC field, and excellent thermal stability is obtained using PBDB-T and ITIC as donor and acceptor, respectively.

Fullerene-Free Polymer Solar Cells with over 11% Efficiency and Excellent Thermal Stability

Over the past three years, a particularly exciting and active area of research within the field of organic photovoltaics has been the use of non-fullerene acceptors (NFAs). Compared with fullerene acceptors, NFAs possess significant advantages including tunability of bandgaps, energy levels, planarity and crystallinity. To date, NFA solar cells have not only achieved impressive power conversion efficiencies of ~13–14%, but have also shown excellent stability compared with traditional fullerene acceptor solar cells. This Review highlights recent progress on single-junction and tandem NFA solar cells and research directions to achieve even higher efficiencies of 15–20% using NFA-based organic photovoltaics are also proposed.

Next-generation organic photovoltaics based on non-fullerene acceptors

Fine energy-level modulations of small-molecule acceptors (SMAs) are realized via subtle chemical modifications on strong electron-withdrawing end-groups. The two new SMAs (IT-M and IT-DM) end-capped by methyl-modified dicycanovinylindan-1-one exhibit upshifted lowest unoccupied molecular orbital (LUMO) levels, and hence higher open-circuit voltages can be observed in the corresponding devices. Finally, a top power conversion efficiency of 12.05% is achieved.

Energy-Level Modulation of Small-Molecule Electron Acceptors to Achieve over 12% Efficiency in Polymer Solar Cells

Advances in the design and application of highly efficient conjugated polymers and small molecules over the past years have enabled the rapid progress in the development of organic photovoltaic (OPV) technology as a promising alternative to conventional solar cells. Among the numerous OPV materials, benzodithiophene (BDT)-based polymers and small molecules have come to the fore in achieving outstanding power conversion efficiency (PCE) and breaking 10% efficiency barrier in the single junction OPV devices. Remarkably, the OPV device featured by BDT-based polymer has recently demonstrated an impressive PCE of 11.21%, indicating the great potential of this class of materials in commercial photovoltaic applications. In this review, we offered an overview of the organic photovoltaic materials based on BDT from the aspects of backbones, functional groups, alkyl chains, and device performance, trying to provide a guideline about the structure-performance relationship. We believe more exciting BDT-based photovol...

Molecular Design of Benzodithiophene-Based Organic Photovoltaic Materials.

All-polymer solar cells have shown great potential as flexible and portable power generators. These devices should offer good mechanical endurance with high power-conversion efficiency for viability in commercial applications. In this work, we develop highly efficient and mechanically robust all-polymer solar cells that are based on the PBDTTTPD polymer donor and the P(NDI2HD-T) polymer acceptor. These systems exhibit high power-conversion efficiency of 6.64%. Also, the proposed all-polymer solar cells have even better performance than the control polymer-fullerene devices with phenyl-C61-butyric acid methyl ester (PCBM) as the electron acceptor (6.12%). More importantly, our all-polymer solar cells exhibit dramatically enhanced strength and flexibility compared with polymer/PCBM devices, with 60- and 470-fold improvements in elongation at break and toughness, respectively. The superior mechanical properties of all-polymer solar cells afford greater tolerance to severe deformations than conventional polymer-fullerene solar cells, making them much better candidates for applications in flexible and portable devices.

http://sciencemission.com/data/attachment.php?id=427&for_session=5f12dcbf83e038a697906b7b1b350568

Flexible, highly efficient all-polymer solar cells

Remarkable progress has been realized in improving the power conversion efficiency (PCE) of polymer solar cells (PSCs) over the past few years, raising the possibility of their commercialization as an alternative counterpart to conventional inorganic solar cells. The development of conjugated polymers that contain various alternately bonded electron-rich (D) and electron-deficient (A) units, called D–A alternating copolymers, plays a crucial role in improving the PCE of PSCs, which has now exceeded 8–9%. However, further development of conjugated polymers is essential to produce highly efficient and stable PSCs with a PCE of more than 10% for commercialization. In this regard, terpolymers, which consist of three different units in the polymer backbone, are promising candidates because they can show synergetic effects of each unit by tuning the composition ratio, thereby enabling full-range absorption, high charge mobility, and good solubility. Substantial progress in the development of terpolymers has been achieved with regard to PCE. Herein, we review the development of terpolymers for PSCs and discuss the major factors that need to be considered in the design of new terpolymers.

Design of terpolymers as electron donors for highly efficient polymer solar cells

A new series of donor–acceptor (D–A) conjugated random terpolymers (PBDTT–DPP–TPD) were synthesized from electron-rich thienyl-substituted benzo[1,2-b:4,5-b′]dithiophene (BDTT), in conjugation with two electron-deficient units, pyrrolo[3,4-c]pyrrole-1,4-dione (DPP) and thieno[3,4-c]pyrrole-4,6-dione (TPD), of different electron-withdrawing strengths. The optical properties of these random terpolymers can be easily controlled by tuning the ratio between DPP and TPD; an increase in TPD induced increased absorption between 400 and 650 nm and a lower highest occupied molecular orbital energy level, while higher DPP contents resulted in stronger absorption between 600 and 900 nm. The best power conversion efficiency (PCE) of 6.33% was obtained from PBDTT–DPP75–TPD25 with [6,6]-phenyl-C71-butyric acid methyl ester (PC71BM) due to the improved light absorption and thus a short-circuit current density (JSC) higher than 16 mA/cm2. Interestingly, the trend observed in the PCE values differed from that of optical be...

Importance of Optimal Composition in Random Terpolymer-Based Polymer Solar Cells

The ability to tune the lowest unoccupied molecular orbital (LUMO)/highest occupied molecular orbital (HOMO) levels of fullerene derivatives used as electron acceptors is crucial in controlling the optical/electrochemical properties of these materials and the open circuit voltage (Voc) of solar cells. Here, we report a series of indene fullerene multiadducts (ICMA, ICBA, and ICTA) in which different numbers of indene solubilizing groups are attached to the fullerene molecule. The addition of indene units to fullerene raised its LUMO and HOMO levels, resulting in higher Voc values in the photovoltaic device. Bulk-heterojunction (BHJ) solar cells fabricated from poly(3-hexylthiophene) (P3HT) and a series of fullerene multiadducts-ICMA, ICBA, and ICTA showed Voc values of 0.65, 0.83, and 0.92 V, respectively. Despite demonstrating the highest Voc value, the P3HT:ICTA device exhibited lower efficiency (1.56%) than the P3HT:ICBA device (5.26%) because of its lower fill factor and current. This result could be ...

Controlling Number of Indene Solubilizing Groups in Multiadduct Fullerenes for Tuning Optoelectronic Properties and Open-Circuit Voltage in Organic Solar Cells

Fullerene tris-adducts have the potential of achieving high open-circuit voltages (VOC) in bulk heterojunction (BHJ) polymer solar cells (PSCs), because their lowest unoccupied molecular orbital (LUMO) level is higher than those of fullerene mono- and bis-adducts. However, no successful examples of the use of fullerene tris-adducts as electron acceptors have been reported. Herein, we developed a ternary-blend approach for the use of fullerene tris-adducts to fully exploit the merit of their high LUMO level. The compound o-xylenyl C60 tris-adduct (OXCTA) was used as a ternary acceptor in the model system of poly(3-hexylthiophene) (P3HT) as the electron donor and the two soluble fullerene acceptors of OXCTA and fullerene monoadduct (o-xylenyl C60 monoadduct (OXCMA), phenyl C61-butyric acid methyl ester (PCBM), or indene-C60 monoadduct (ICMA)). To explore the effect of OXCTA in ternary-blend PSC devices, the photovoltaic behavior of the device was investigated in terms of the weight fraction of OXCTA (WOXCTA...

Tae Eui Kang

Papers

Flexible, highly efficient all-polymer solar cells

Design of terpolymers as electron donors for highly efficient polymer solar cells

Importance of Optimal Composition in Random Terpolymer-Based Polymer Solar Cells

Controlling Number of Indene Solubilizing Groups in Multiadduct Fullerenes for Tuning Optoelectronic Properties and Open-Circuit Voltage in Organic Solar Cells

Effect of Fullerene Tris-adducts on the Photovoltaic Performance of P3HT:Fullerene Ternary Blends