Role of 3,4-Ethylenedioxythiophene in the Enhancement of Optical and Charge Transport Properties of Low Band Gap Diketopyrrolopyrrole-Containing Metallooligomers Designed for Organic Solar Cells

ACS APPLIED ENERGY MATERIALS(2023)

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摘要
3,4-Ethylenedioxythiophene (EDOT) diketopyrrolopyrrole (DPP)-containing metallooligomer P5 with platinum complex trans-Pt(PBu3)(2)(C equivalent to C)(2) was synthesized and characterized. The optical and electrochemical properties of P5 are compared to those of previously reported metallooligomers. The insertion of EDOT into the conjugated backbone leads to a decrease in the optical band gap of P5 to 1.48 eV and a broadening of the spectral absorption range (350-840 nm) in agreement with density functional theory (DFT) and time dependent density functional theory (TDDFT) calculations. The structuring effect of EDOT favors a higher planarity of the chain as evidenced on optimized geometry from DFT calculations. Steady state and time-resolved absorption and fluorescence spectroscopy reveal an excellent chemical stability of P5 and permitted to establish a mechanism of formation and relaxation of the electron-hole pair in the P5/PC71BM blend film: (1) The excitation of the polymer (<52.5 ps) P5 + h nu -> P5*, (2) an ultrafast electron transfer (179 fs), P5* + PC71BM -> P5(center dot+) + PC71BM center dot-, and (3) a back electron transfer (1.8 and 25 ps), P5(center dot+) + PC71BM center dot- -> (1,3)(P5)* + PC71BM with triplet state relaxation (6.5 ns). The rate constant for electron transfer is 3.5 x 10(12) s(-1). Bulk heterojunction solar cells were fabricated using an active layer prepared from the blend of P5 as the donor with each acceptor PC71BM, IT-4F, or Y6. Good power conversion efficiencies (PCE) are reached with PC71BM (PCE = 9.46%), but they are higher with IT-4F (PCE = 11.02%) and reach a maximum value with Y6 (PCE = 14.81%). This work highlights the beneficial role of EDOT on the enhancement of solar cell properties with the increase of charge mobilities and external quantum efficiency. The highest value of PCE obtained with P5:Y6 (15.03%) is a record-high PCE for any [Pt]-containing polyyne oligomers.
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关键词
solar cell,metallooligomers,3,4-ethylenedioxythiophene,planarity,nonfullerene acceptors
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