Photoinduced Charge Transfer in Donor鈥揂cceptor (DA) Copolymer: Fullerene Bis-adduct Polymer Solar Cells

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• 作者：Tae Eui Kang ; Han-Hee Cho ; Chul-Hee Cho ; Ki-Hyun Kim ; Hyunbum Kang ; Myounghee Lee ; Sunae Lee ; BongSoo Kim ; Chan Im ; Bumjoon J. Kim
• 刊名：ACS Applied Materials & Interfaces
• 出版年：2013
• 出版时间：February 13, 2013
• 年：2013
• 卷：5
• 期：3
• 页码：861-868
• 全文大小：545K
• 年卷期：v.5,no.3(February 13, 2013)
• ISSN：1944-8252

文摘

Polymer solar cells (PSCs) consisting of fullerene bis-adduct and poly(3-hexylthiophene) (P3HT) blends have shown higher efficiencies than P3HT:phenyl C₆₁-butyric acid methyl ester (PCBM) devices, because of the high-lying lowest unoccupied molecular orbital (LUMO) level of the fullerene bis-adducts. In contrast, the use of fullerene bis-adducts in donor鈥揳cceptor (DA) copolymer systems typically causes a decrease in the device鈥檚 performance due to the decreased short-circuit current (J_SC) and the fill factor (FF). However, the reason for such poor performance in DA copolymer:fullerene bis-adduct blends is not fully understood. In this work, bulk-heterojunction (BHJ)-type PSCs composed of three different electron donors with four different electron acceptors were chosen and compared. The three electron donors were (1) poly[(4,8-bis-(2-ethylhexyloxy)benzo[1,2-b:4,5-b鈥瞉dithiophene)-2,6-diyl-alt-(5-octylthieno[3,4-c]pyrrole-4,6-dione)-1,3-diyl] (PBDTTPD), (2) poly[(4,8-bis-(2-ethylhexyloxy)benzo[1,2-b:4,5-b鈥瞉dithiophene)-2,6-diyl-alt-(4-(2-ethylhexanoyl)-thieno[3,4-b]thiophene)-2,6-diyl] (PBDTTT-C), and (3) P3HT polymers. The four electron acceptors were (1) PCBM, (2) indene-C₆₀ monoadduct (ICMA), (3) indene-C₆₀ bis-adduct (ICBA), and (4) indene-C₆₀ tris-adduct (ICTA). To understand the difference in the performance of BHJ-type PSCs for the three different polymers in terms of the choice of fullerene acceptor, the structural, optical, and electrical properties of the blends were measured by the external quantum efficiency (EQE), photoluminescence, grazing incidence X-ray scattering, and transient absorption spectroscopy. We observed that while the molecular packing and optical properties cannot be the main reasons for the dramatic decrease in the PCE of the DA copolymers and ICBA, the value of the driving force for charge transfer (螖G_CT) is a key parameter for determining the change in J_SC and device efficiency in the DA copolymer- and P3HT-based PSCs in terms of fullerene acceptor. The low EQE and J_SC in PBDTTPD and PBDTTT-C blended with ICBA and ICTA were attributed to an insufficient 螖G_CT due to the higher LUMO levels of the fullerene multiadducts. Quantitative information on the efficiency of the charge transfer was obtained by comparing the polaron yield, lifetime, and exciton dissociation probability in the DA copolymer:fullerene acceptor films.

Keywords:

photoinduced charge transfer; driving force for charge transfer (螖G_CT); donor鈭抋cceptor (DA) copolymer; fullerene bis-adduct; polymer solar cell