Ye-Jin Hwang

7.7% Efficient All-Polymer Solar Cells.

By controlling the polymer/polymer blend self-organization rate, all-polymer solar cells composed of a high-mobility, crystalline, naphthalene diimide-selenophene copolymer acceptor and a benzodithiophene-thieno[3,4-b]thiophene copolymer donor are achieved with a record 7.7% power conversion efficiency and a record short-circuit current density (18.8 mA cm(-2)).

All-Polymer Solar Cells with 3.3% Efficiency Based on Naphthalene Diimide-Selenophene Copolymer Acceptor

The lack of suitable acceptor (n-type) polymers has limited the photocurrent and efficiency of polymer/polymer bulk heterojunction (BHJ) solar cells. Here, we report an evaluation of three naphthalene diimide (NDI) copolymers as electron acceptors in BHJ solar cells which finds that all-polymer solar cells based on an NDI-selenophene copolymer (PNDIS-HD) acceptor and a thiazolothiazole copolymer (PSEHTT) donor exhibit a record 3.3% power conversion efficiency. The observed short circuit current density of 7.78 mA/cm(2) and external quantum efficiency of 47% are also the best such photovoltaic parameters seen in all-polymer solar cells so far. This efficiency is comparable to the performance of similarly evaluated [6,6]-Phenyl-C61-butyric acid methyl ester (PC60BM)/PSEHTT devices. The lamellar crystalline morphology of PNDIS-HD, leading to balanced electron and hole transport in the polymer/polymer blend solar cells accounts for its good photovoltaic properties.

n-Type Semiconducting Naphthalene Diimide-Perylene Diimide Copolymers: Controlling Crystallinity, Blend Morphology, and Compatibility Toward High-Performance All-Polymer Solar Cells

Knowledge of the critical factors that determine compatibility, blend morphology, and performance of bulk heterojunction (BHJ) solar cells composed of an electron-accepting polymer and an electron-donating polymer remains limited. To test the idea that bulk crystallinity is such a critical factor, we have designed a series of new semiconducting naphthalene diimide (NDI)-selenophene/perylene diimide (PDI)-selenophene random copolymers, xPDI (10PDI, 30PDI, 50PDI), whose crystallinity varies with composition, and investigated them as electron acceptors in BHJ solar cells. Pairing of the reference crystalline (crystalline domain size Lc = 10.22 nm) NDI-selenophene copolymer (PNDIS-HD) with crystalline (Lc = 9.15 nm) benzodithiophene-thieno[3,4-b]thiophene copolymer (PBDTTT-CT) donor yields incompatible blends, whose BHJ solar cells have a power conversion efficiency (PCE) of 1.4%. However, pairing of the new 30PDI with optimal crystallinity (Lc = 5.11 nm) as acceptor with the same PBDTTT-CT donor yields compatible blends and all-polymer solar cells with enhanced performance (PCE = 6.3%, Jsc = 18.6 mA/cm(2), external quantum efficiency = 91%). These photovoltaic parameters observed in 30PDI:PBDTTT-CT devices are the best so far for all-polymer solar cells, while the short-circuit current (Jsc) and external quantum efficiency are even higher than reported values for [70]-fullerene:PBDTTT-CT solar cells. The morphology and bulk carrier mobilities of the polymer/polymer blends varied substantially with crystallinity of the acceptor polymer component and thus with the NDI/PDI copolymer composition. These results demonstrate that the crystallinity of a polymer component and thus compatibility, blend morphology, and efficiency of polymer/polymer blend solar cells can be controlled by molecular design.

Nonfullerene Polymer Solar Cells with 8.5% Efficiency Enabled by a New Highly Twisted Electron Acceptor Dimer.

Fullerene-free and processing additive-free 8.5% efficient polymer solar cells are achieved by using a new 3,4-ethylenedioxythiophene-linked arylene diimide dimer with a 76° twist angle. The devices combine high (78-83%) external quantum efficiency with high (0.91-0.95 V) photovoltages and thus have relatively low optical bandgap energy loss.

All‐Polymer Bulk Heterojuction Solar Cells with 4.8% Efficiency Achieved by Solution Processing from a Co‐Solvent

All-polymer solar cells with 4.8% power conversion efficiency are achieved via solution processing from a co-solvent. The observed short-circuit current density of 10.5 mA cm(-2) and external quantum efficiency of 61.3% are also the best reported in all-polymer solar cells so far. The results demonstrate that processing the active layer from a co-solvent is an important strategy in achieving highly efficient all-polymer solar cells.

Fine‐Tuning the 3D Structure of Nonfullerene Electron Acceptors Toward High‐Performance Polymer Solar Cells

Arylene linkers in a series of new tetraaza-benzodifluoranthene diimide dimers enable tuning of the 3D molecular structure of nonfullerene electron acceptors, facilitating observation of dramatic variation of the power conversion efficiency from 2.6% to 6.4% as the twist angle between the monomeric building blocks in the dimer is varied.

New n-type polymer semiconductors based on naphthalene diimide and selenophene derivatives for organic field-effect transistors

n-Type conjugated polymers based on naphthalene diimide (NDI) and various selenophene derivatives have been synthesized, characterized and evaluated as semiconductors for n-channel organic field-effect transistors (OFETs). The new poly(naphthalene diimides) (PNDIs) have weight average molecular weights of 12–107 kDa with a polydispersity of 1.1–2.6. These PNDIs combined a constant electron affinity of 3.9 eV with an optical band gap that varies from 1.7 eV in PNDISS to 1.4 eV in ePNDIBS due to intramolecular charge transfer. X-ray diffraction analysis of films of the polymers revealed a lamellar crystalline structure in which the lamellar interchain distance varied from 2.45 nm in PNDISS to 2.75 nm in PNDIBDS while the π-stacking distance varied from 0.397 nm in PNDIBDS to 0.443 nm in PNDISS. Average field-effect electron mobility of 0.008 to 0.24 cm2 V−1 s−1 with high on/off current ratio (104 to 106) was observed from the bottom gate/top contact n-channel OFETs. A 3.4-fold enhancement in electron mobility was observed in phenyl end-capped and high molecular weight ePNDIBS whereas such end-capping had no effect on the electron mobility in PNDISS and PNDIBDS.

Annealing temperature dependence of the efficiency and vertical phase segregation of polymer/polymer bulk heterojunction photovoltaic cells

We report observation of annealing temperature-induced simultaneous vertical phase segregation and large enhancement of power conversion efficiency (PCE) of all-polymer bulk heterojunction (BHJ) solar cells composed of a poly(3-hexylthiophene) (P3HT) donor and a naphthalene diimide-selenolo[3,2-b]selenophene copolymer (PNDISS) acceptor. The PCE of P3HT:PNDISS BHJ devices increased over 50-fold from 0.04% to 2.03% when the annealing temperature was increased from 50 to 150 °C. Absorption spectroscopy and photoluminescence quenching experiments provide evidence of increasing phase segregation of the polymer/polymer blend films with increasing annealing temperature. Field-effect charge transport, contact angle, surface energy, and variable angle ellipsometry measurements on the P3HT:PNDISS blend films showed that thermal annealing induced vertical phase segregation, whereby the low surface energy polymer (P3HT) migrated to the bulk, while the high surface energy polymer (PNDISS) enriches at the substrate/ble...