N-Octyl-2,7-dithia-5-azacyclopenta[a]pentalene-4,6-dione-Based Low Band Gap Polymers for Efficient Solar Cells

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• 作者：Seul-Ong Kim ; Youn-Su Kim ; Hui-Jun Yun ; Il Kang ; Youngwoon Yoon ; Nara Shin ; Hae Jung Son ; Honggon Kim ; Min Jae Ko ; BongSoo Kim ; Kyungkon Kim ; Yun-Hi Kim ; Soon-Ki Kwon
• 刊名：Macromolecules
• 出版年：2013
• 出版时间：May 28, 2013
• 年：2013
• 卷：46
• 期：10
• 页码：3861-3869
• 全文大小：527K
• 年卷期：v.46,no.10(May 28, 2013)
• ISSN：1520-5835

文摘

We report the synthesis, characterization, and solar cell properties of new donor鈥揳cceptor-type low band gap polymers (POBDTPD and PEBDTPD) that incorporate dialkoxybenzodithiophene (BDT) as the donor and N-octyl-2,7-dithia-5-azacyclopenta[a]pentalene-4,6-dione (DTPD) as the acceptor. The newly developed DTPD moiety was carefully designed to lower a band gap via strong interaction between donor鈥揳cceptor moieties and keep polymer energy levels deep. Remarkably, the DTPD acceptor moiety effectively widens the light absorption range of the polymers up to 900 nm while positioning their HOMO and LUMO levels in the optimal range, i.e., 鈭?.3 and 鈭?.0 eV, respectively, for high power conversion efficiencies (PCEs) as we intended. Solar cell devices were fabricated according to the structure ITO/PEDOT:PSS/photoactive (polymer:PC₇₀BM)/TiO₂/Al. The POBDTPD devices exhibited a PCE of 4.7% with a V_oc of 0.70 V, a J_sc of 10.6 mA/cm², and a FF of 0.64. The PEBDTPD devices yielded a higher PCE of 5.3% with a V_oc of 0.72 V, a J_sc of 13.5 mA/cm², and a FF of 0.54. AFM, TEM, and PL quenching measurements revealed that the high J_scs are a result of the appropriate morphology and efficient charge separation. In comparing the performances of the two polymer devices, the higher J_sc for the PEBDTPD device was attributed to its better nanoscale phase separation, smoother surface, and higher carrier mobility in the polymer:PC₇₀BM blend films. The higher FF for the POBDTPD device was ascribed to a good balance between the hole and electron mobilities. Overall, we demonstrate that the DTPD unit is a promising electron-accepting moiety to develop high performance low band gap polymers.