An ester-functionalized diketopyrrolopyrrole molecule with appropriate energy levels for application in solution-processed organic solar cells

Abstract

For highly efficient organic solar cells (OSCs), the electron donor should possess not only a narrow band gap (E g ) but also a low highest occupied molecular orbital (HOMO) energy level. To achieve it, in this paper, we designed and synthesized a diketopyrrolopyrrole (DPP) derivative end capped with an ethyl thiophene-2-carboxylate moiety, 3,6-bis{5-[(ethyl thiophene-2-carboxylate)-2-yl]thiophene-2-yl}-2,5-bis(2-ethylhexyl)pyrrolo[3,4-c]pyrrole-1,4-dione (DPP(CT) 2 ). Through UV-vis absorption and cyclic voltammetry (CV) measurements, we demonstrated that the resulting molecule exhibits both a low optical E g of 1.65 eV and a lower-lying HOMO energy level of À5.33 eV owing to the electronegativity of the ester group and the conjugation effect of the thiophene ring. Therefore, when DPP(CT) 2 is used as the electron donor to blend with [6,6]-phenyl-C 71 -butyric acid methyl ester (PC 71 BM) for solution processable OSCs, a power conversion efficiency (PCE) of 4.02% combined with an open-circuit voltage (V OC ) as high as 0.94 V and a broad photovoltaic response range extending to around 750 nm is obtained.

Mechanisms of Nanoporous Alumina Formation and Self-organized Growth

“…As a result, a morphology of ordered, upright, and uniform arrangement structure of branched pores is obtained (Fig. 1.21d) [69].…”

“…As shown in Fig. 1.17, ordered arrangement of pores can be achieved only for the reduction of anodization voltage by the factors of ffiffi ffi 3 p , ffiffi ffi 4 p and their common multiples and powers [68]. Otherwise, number of the branched pores can't be the same from each of the stem pores.…”

Efficient ternary blend polymer solar cells with a bipolar diketopyrrolopyrrole small molecule as cascade material

“…With increasing the fraction of F(DPP) 2 B 2 in fullerene, both of the hole and electron mobilities are decreased slightly for the ternary blends of P3HT:F(DPP) 2 B 2 :PC 61 BM. This phenomenon is reasonable since it is natural that a lower PC 61 BM concentration is less beneficial to form percolated electron transport pathways [40]. Moreover, we find that the ternary blends exhibit relatively similar and balanced hole/electron transport when the F(DPP) 2 B 2 content is below 20%, which are corresponding to their good device performance.…”

Organic Semiconductor Photovoltaic Materials

“…Chen and coworkers reported an ethyl thiophene-2-carboxylate group end-capped DPP molecule, 2i. Benefiting from its narrow bandgap and lower-lying HOMO, the OSCs based on 2i showed a broad photovoltaic response range extending to around 750 nm and a very high V OC of 0.94 V, affording a PCE of 4.02 % [32]. Using triazatruxene as the end-capper group and DPP as the central group, Ziessel, Leclerc and coworkers reported the synthesis and photovoltaic properties of dumbbellshaped solution-processable 2j.…”