Browsing by Author "Chang, Bin"

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Engineering the Core Units of Small-Molecule Acceptors to Enhance the Performance of Organic Photovoltaics
(1970-01-01)
Wang, Hao-Cheng
;
Chen, Chung-Hao
;
Li, Ren-Hao
;
Lin, Yu-Che
;
Tsao, Cheng-Si
Understanding the chemical structures of next-generation small molecules is a critical step for increasing the performance of organic photovoltaics (OPVs); an OPV's small molecule determines not only the extent of light absorption but also the morphology. Herein, four small molecules featuring different cores-indaceno dithiophene, dithienoindeno indaceno dithiophene (IDTT), substituted IDTT, and dithienothiophene-pyrrolobenzothiadiazole-denoted as ID-4Cl, IT-4Cl, m-ITIC-OR-4Cl, and Y7, respectively, are selected to form active layers with poly(quinoxaline) (PTQ10) and poly(benzodithiophene-4,8-dione) (PM6). The Y7 devices exhibit the best performance in both systems, with the power conversion efficiency (PCE) reaching 14.5%; in comparison, ID-4Cl device gives a PCE of 10.0% for blending with PTQ10 and a relative efficiency enhancement of 45%. The same trend occurs for the cases of PM6 blend devices. This enhancement is attributed to i) the improved short-circuit current density that is provided by the greater degree of conjugation in S, N-heteroarenes ladder-type fused-ring cores of Y7, ii) an induced face-on Y7 orientation and smaller domain sizes that result from the sp(2)-hybridized nitrogen side chain, and iii) smaller energy loss. This study reveals the importance of the core structure on the device performance and provides guidelines for the design of new materials for OPV technologies.
Hydrogen plasma-treated MoSe2 nanosheets enhance the efficiency and stability of organic photovoltaics
(2019-10-07)
Wang, Hao-Cheng
;
Lin, Yu-Che
;
Chen, Chung-Hao
;
Huang, Chi-Hsien
;
Chang, Bin
In this paper we report the effect on the power conversion efficiency (PCE) and stability of photovoltaic devices after incorporating hydrogenated two-dimensional (2D) MoSe2 nanosheets into the active layer of bulk heterojunction (BHJ) organic photovoltaics (OPV). The surface properties of 2D MoSe2 nanosheets largely affect their dispersion in the active layer blend and, thus, influence the carrier mobility, PCE, and stability of corresponding devices. We treated MoSe2 nanosheets with hydrogen plasma and investigated their influence on the polymer packing and fullerene domain size of the active layer. For the optimized devices incorporating 37.5 wt% of untreated MoSe2, we obtained a champion PCE of 9.82%, compared with the champion reference PCE of approximately 9%. After incorporating the hydrogen plasma-treated MoSe2 nanosheets, we achieved a champion PCE of 10.44%-a relative increase of 16% over that of the reference device prepared without MoSe2 nanosheets. This PCE is the one of the highest ever reported for OPVs incorporating 2D materials. We attribute this large enhancement to the enhanced exciton generation and dissociation at the MoSe2-fullerene interface and, consequently, the balanced charge carrier mobility. The device incorporating the MoSe2 nanosheets maintained 70% of its initial PCE after heat-treatment at 100 degrees C for 1 h; in contrast, the PCE of the reference device decreased to 60% of its initial value-a relative increase in stability of 17% after incorporating these nanosheets. We also incorporated MoSe2 nanosheets (both with and without treatment) into a polymer donor (PBDTTBO)/small molecule (IT-4F) acceptor system. The champion PCEs reached 7.85 and 8.13% for the devices incorporating the MoSe2 nanosheets with and without plasma treatment, respectively-relative increases of 8 and 12%, respectively, over that of the reference. These results should encourage a push toward the implementation of transition metal dichalcogenides to enhance the performances of BHJ OPVs.