Improved Performance for Inverted Organic Photovoltaics via Spacer between Benzodithiophene and Benzothiazole in Polymers

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• 作者：Lal Mohammad ; Qiliang Chen ; Abu Mitul ; Jianyuan Sun ; Devendra Khatiwada ; Bjorn Vaagensmith ; Cheng Zhang ; Jing Li ; Qiquan Qiao
• 刊名：Journal of Physical Chemistry C
• 出版年：2015
• 出版时间：August 20, 2015
• 年：2015
• 卷：119
• 期：33
• 页码：18992-19000
• 全文大小：701K
• ISSN：1932-7455

文摘

In this work, the effects of the spacer between benzo[1,2-b;3,4-b鈥瞉dithiophene (BDT) and dialkoxybenzothiadiazole (ROBT) in polymers were investigated for applications in organic solar cells. Polymer PBDT鈥?T鈥揜OBT has a bithiophene (2T) spacer between the BDT and ROBT units, whereas PBDT鈥揜OBT is a direct copolymer of BDT and ROBT. The polymer/PC₇₀BM solar cells using both polymers were fabricated and optimized via polymer/fullerene ratio, solvent, and solvent additives. The spacer has significantly improved solar cell performance from 1.28% (V_oc =0.77 V, J_sc = 3.13 mA/cm², FF = 53.11%) to 5.11% (V_oc = 0.66 V, J_sc = 13.33 mA/cm², FF = 58.12%). The X-ray diffraction (XRD) spectra show the PBDT鈥?T鈥揜OBT/PC₇₀BM blended film is semicrystalline, whereas the PBDT鈥揜OBT/PC₇₀BM film is amorphous. This indicates that the spacer facilitates polymer organization for higher carrier mobility in the film. Atomic force microscopy (AFM) topography and phase images show that PBDT鈥?T鈥揜OBT/PC₇₀BM films form fibrillar networks, whereas PBDT鈥揜OBT/PC₇₀BM films exhibit larger granular morphology. The photoinduced charge extraction by linearly increasing voltage (Photo-CELIV) measurements show that PBDT鈥?T鈥揜OBT/PC₇₀BM has a mobility of 9.59 脳 10^鈥? cm²/(V路s), which is higher than the mobility of 8.64 脳 10^鈥? cm²/(V路s) for PBDT鈥揜OBT/PC₇₀BM film.