Zhang, T.T.ZhangHan, H.H.HanZou, Y.Y.ZouLee, Y.-C.Y.-C.LeeOshima, H.H.OshimaWong, K.-T.K.-T.WongHolmes, R.J.R.J.Holmes2019-07-312019-07-312017https://www.scopus.com/inward/record.uri?eid=2-s2.0-85026751644&doi=10.1021%2facsami.7b05304&partnerID=40&md5=fcc4f799c209698697af7022c566c971https://scholars.lib.ntu.edu.tw/handle/123456789/415841We report a promising set of donor-acceptor-acceptor (D-A-A) electron-donor materials based on coplanar thieno[3,2-b]/[2,3-b]indole, benzo[c][1,2,5]thiadiazole, and dicyanovinylene, which are found to show broadband absorption with high extinction coefficients. The role of the regioisomeric electron-donating thienoindole moiety on the physical and structural properties is examined. Bulk heterojunction (BHJ) organic photovoltaic cells (OPVs) based on the thieno[2,3-b]indole-based electron donor NTU-2, using C70 as an electron acceptor, show a champion power conversion efficiency of 5.2% under AM 1.5G solar simulated illumination. This efficiency is limited by a low fill factor (FF), as has previously been the case in D-A-A systems. In order to identify the origin of the limited FF, further insight into donor layer charge-transport behavior is realized by examining planar heterojunction OPVs, with emphasis on the evolution of film morphology with thermal annealing. Compared to as-deposited OPVs that exhibit insufficient donor crystallinity, crystalline OPVs based on annealed thin films show an increase in the short-circuit current density, FF, and power conversion efficiency. These results suggest that that the crystallization of D-A-A molecules might not be realized spontaneously at room temperature and that further processing is needed to realize efficient charge transport in these materials. © 2017 American Chemical Society.charge collection; crystallinity; organic photovoltaic cells; push-pull molecules; thermal annealing[SDGs]SDG7Annealing; Efficiency; Electrons; Heterojunctions; Molecules; Photoelectrochemical cells; Photovoltaic cells; Polycyclic aromatic hydrocarbons; Solar power generation; Charge collection; Crystallinities; Organic photovoltaic cells; Push-pull molecules; Thermal-annealing; Conversion efficiencyjournal article10.1021/acsami.7b053042-s2.0-85026751644