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Issue 1, 2014
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Theoretical investigations on fluorinated and cyano copolymers for improvements of photovoltaic performances

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Abstract

An effective way to improve the efficiency of organic solar cells is to adjust the electron-withdrawing strength in donor–acceptor (D–A) copolymers. To achieve this goal, starting from previously reported polymers (PCPDT-BT and PDTPr-FBT) which are based on benzothiadiazole (BT) electron-deficient unit connected to each of two electron-rich units (cyclopentadithiophene (CPDT) and dithienopyrrole (DTPr)), we introduced two strong electron-withdrawing fluorine atoms or a cyano group on the BT unit to replace BT with fluorinated BT (FBT) and cyano BT (CNBT) in PCPDT-BT and PDTPr-FBT, respectively, and designed two types of D–A copolymers with different electron-withdrawing strengths. From the calculated results, the introduction of strong electron-withdrawing groups onto the copolymer can not only obviously reduce the HOMO and LUMO level of molecules, which results in increasing the open circuit voltage (Voc) in solar cells, but can also enhance light-absorbing efficiency and charge transport ability of polymers. In the meantime, the cyano copolymers of PCPDT-1CNBT and PDTPr-1CNBT show the best performances with the smallest band gaps, lowest HOMO energy levels, the highest Voc, and the largest hole mobility (3.67 × 10−3 cm2 V−1 s−1 and 8.05 × 10−4 cm2 V−1 s−1, respectively) among all the considered systems. The power conversion efficiencies (PCEs) of ∼7.2% and ∼6.8% for organic solar cell made of designed polymers (PCPDT-1CNBT and PDTPr-1CNBT) are predicted by Scharber models. We presented several polymer donors for comparison of how the strong electron-withdrawing group influences the electronic properties and optical absorption of the polymers and the performances of organic solar cells made of the polymers, thereby obtaining promising organic solar cells with high power conversion efficiencies.

Graphical abstract: Theoretical investigations on fluorinated and cyano copolymers for improvements of photovoltaic performances

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Publication details

The article was received on 01 Aug 2013, accepted on 14 Oct 2013 and first published on 17 Oct 2013


Article type: Paper
DOI: 10.1039/C3CP53268B
Citation: Phys. Chem. Chem. Phys., 2014,16, 311-323
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    Theoretical investigations on fluorinated and cyano copolymers for improvements of photovoltaic performances

    X. Liu, M. Li, R. He and W. Shen, Phys. Chem. Chem. Phys., 2014, 16, 311
    DOI: 10.1039/C3CP53268B

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