Synthesis and photovoltaic properties of small molecule electron acceptors with twin spiro-type core structure

Synthesis and photovoltaic properties of small molecule electron acceptors with twin spiro-type core structur

Organic solar cells based on non-fullerene acceptors of nine fused-ring by modifying end groups

A series of small molecule acceptors (SMAs) based on a benzodithiophene-pyrrolobenzothiadiazole-based nine fused-ring core and different end groups of 2-(5,6-difluoro-3-oxo-2,3-dihydro-1H-inden-1-ylidene) malononitrile (2FIC), 3-(dicyanomethylene)indian-1-one (IC) and 2-(3-ethyl-4-oxo-thiazolidin-2-ylidene) malononitrile (RCN) have been designed and synthesized. The SMAs X94FIC, X9IC, X9Rd and X9T4FIC were chosen as electron acceptors with blending the donor polymer PBDB-T to prepare the organic solar cells (OSCs) and investigate photoelectric performance. Surprisingly, X94FIC showed an excellent photo-response up to 1000 nm, while X9IC and X9T4FIC also possess a photo-response to 900 nm. A power conversion efficiency (PCE) of 7.08% was obtained for the active layers PBDB-T:X94FIC. This result demonstrates that small molecule acceptor containing the nine fused-ring core and the end group with di-fluorine atoms is promising candidate for the development of high performance non-fullerene OSCs

Efficient ternary organic solar cells based on a twin spiro-type non-fullerene acceptor

Efficient ternary organic solar cells based on a twin spiro-type non-fullerene accepto

Benzodifuran-Based ?-Conjugated Copolymers for Bulk Heterojunction Solar Cells

Novel ?-conjugated copolymers based on a sol. electroactive benzo[1,2-b:4,5-b']difuran (BDF) chromophore have been synthesized by the introduction of thiophene/benzo[c][1,2,5]thiadiazole/9-phenylcarbazole comonomer units. These copolymers cover broad absorption ranges (250-700 nm) with narrow optical band gaps of 1.71-2.01 eV. Moreover, their band gaps as well as their mol. electronic energy levels are readily tuned by copolymg. the BDF core with different ?-conjugated electron-donating or withdrawing units in different ratios. Bulk heterojunction solar cell devices are fabricated using the copolymers as the electron donor and PCBM ([6,6]-phenyl-C61-butyric acid Me ester) as the electron acceptor. Preliminary research has revealed power conversion efficiencies of 0.17-0.59% under AM 1.5 illumination (100 mW/cm2). [on SciFinder(R)

Soft phonon modes from off-center Ge atoms lead to ultralow thermal conductivity and superior thermoelectric performance in n-type PbSe–GeSe

Historically PbSe has underperformed PbTe in thermoelectric efficiency and has been regarded as an inferior relative to its telluride congener. However, the fifty-fold greater natural abundance of Se relative to Te makes PbSe appealing as a thermoelectric material. We report that the n-type GeSe-alloyed PbSe system achieves a peak figure of merit, ZT, of ∼1.54 at 773 K and maintains ZT values above 1.2 over a broad temperature range from 623 K to 923 K. The highest performing composition is Sb-doped PbSe–12%GeSe, which exhibits an ultralow lattice thermal conductivity of ∼0.36 W m−1 K−1 at 573 K, close to the limit of amorphous PbSe. Theoretical studies reveal that the alloyed Ge2+ atoms prefer to stay at off-center lattice positions, inducing low frequency modes. The Ge atoms also cause the unexpected behavior where the next nearest atom neighbors (6 Pb atoms) oscillate at lower frequencies than in pure PbSe leading to a large reduction of the Debye temperature and acoustic phonon velocity. The Pb0.9955Sb0.0045Se–12%GeSe system also shows Ge-rich precipitates and many aligned dislocations within its microstructure which also contribute to phonon scattering. The resultant average ZT (ZTavg), a broad measure of the material's potential for functional thermoelectric modules, is 1.06 from 400 K to 800 K, the highest among all previously reported n- and p-type PbSe. This value matches or exceeds even those of the best n-type PbTe-based thermoelectric materials

Synthesis, Structural Characterization, and Field-Effect Transistor Properties of <i>n</i>‑Channel Semiconducting Polymers Containing Five-Membered Heterocyclic Acceptors: Superiority of Thiadiazole Compared with Oxadiazole

Five-membered 1,3,4-oxadiazole (OZ) and 1,3,4-thiadiazole (TZ) heterocycle-based copolymers as active layer have long been ignored in solution-processable <i>n</i>-channel polymer field-effect transistors (PFETs) despite the long history of using OZ or TZ derivatives as the electron-injecting materials in organic light-emitting devices and their favorable electron affinities. Herein, we first report the synthesis and PFETs performance of two <i>n</i>-channel conjugated polymers bearing OZ- or TZ-based acceptor moieties, i.e., PNOZ and PNTZ, where simple thiophene units are utilized as the weak donors and additional alkylated-naphthalenediimides units are used as the second acceptors. A comparative study has been performed to reveal the effect of different heterocyclic acceptors on thermal properties, electronic properties, ordering structures, and carrier transport performance of the target polymers. It is found that both polymers possess low-lying LUMO values below −4.0 eV, indicating high electron affinity for both heterocycle-based polymers. Because of strong polarizable ability of sulfur atom in TZ heterocycle, PNTZ exhibits a red shift in maximal absorption and stronger molecular aggregation even in the diluted chlorobenzene solution as compared to the OZ-containing PNOZ. Surface morphological study reveals that a nodule-like surface with a rough surface morphology is observed clearly for PNOZ films, whereas PNTZ films display highly uniform surface morphology with well interconnected fiber-like polycrystalline grains. Investigation of PFETs performance indicates that both polymers afford air-stable <i>n</i>-channel transport characteristics. The uniform morphological structure and compact π–π stacking endow PNTZ with a high electron mobility of 0.36 cm² V^–1 s^–1, much higher than that of PNOZ (0.026 cm² V^–1 s^–1). These results manifest the feasibility in improving electron-transporting property simply by tuning heteroatom substitutes in <i>n</i>-channel polymers; further demostrate that TZ derivatives possess much superior potential for developing high-performance <i>n</i>-channel polymers compared to OZ derivatives