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Issue 10, 2017
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Comparing non-fullerene acceptors with fullerene in polymer solar cells: a case study with FTAZ and PyCNTAZ

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Abstract

Non-fullerene acceptors (NFAs) are becoming a serious contender to fullerene-based electron acceptors in organic photovoltaics, due to their structural versatility and easily tunable optical and electronic properties. However, NFA-based solar cells often have a decreased short-circuit current (Jsc) and fill factor (FF) compared to their fullerene-based counterparts. Here, we investigate the fundamental causes of this decrease in the performance of solar cells using a non-fullerene acceptor (SF-PDI2) paired with two polymer donors, FTAZ and PyCNTAZ, compared with their fullerene-based counterparts. Through a number of experimental techniques and morphological studies, we show that the SF-PDI2-based solar cells suffer from insufficient charge generation, transport, and collection when compared with the PCBM-based solar cells. The SF-PDI2-based solar cells show increased bimolecular recombination, which, together with other recombination loss mechanisms in these cells, causes a significant decrease in their Jsc and FF. Notably, the less pure domains, low electron mobility (on the order of 10−5 cm2 V−1 s−1), and imbalanced mobility (in regard to the hole mobility) further explain the low FF. On the other hand, the higher open-circuit voltage (Voc) in the SF-PDI2 devices is mainly due to the increase in the CT state energy. It is worth mentioning that the PyCNTAZ-based devices show an ultralow charge separation energy (ΔECS), close to 0 eV. Our results demonstrate that further increasing the mobility (both of electrons and holes) in these NFA-based solar cells would be a viable approach to further enhance the efficiency of these new types of solar cells, ideally, without losing the high Voc of such cells.

Graphical abstract: Comparing non-fullerene acceptors with fullerene in polymer solar cells: a case study with FTAZ and PyCNTAZ

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Publication details

The article was received on 05 Dec 2016, accepted on 01 Feb 2017 and first published on 02 Feb 2017


Article type: Paper
DOI: 10.1039/C6TA10450A
J. Mater. Chem. A, 2017,5, 4886-4893

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    Comparing non-fullerene acceptors with fullerene in polymer solar cells: a case study with FTAZ and PyCNTAZ

    N. Bauer, Q. Zhang, J. Zhao, L. Ye, J. Kim, I. Constantinou, L. Yan, F. So, H. Ade, H. Yan and W. You, J. Mater. Chem. A, 2017, 5, 4886
    DOI: 10.1039/C6TA10450A

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