Similar or different: the same Spiro-core but different alkyl chains with apparently improved device performance of perovskite solar cells

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  • ReceivedNov 7, 2018
  • AcceptedJan 28, 2019
  • PublishedFeb 25, 2019


By intelligently utilizing the odd-even effect existing in the melting points of alkanes as presented in the basic textbook of Organic Chemistry, different alkoxy groups were introduced to modify the structure of commercial Spiro-OMeTAD to give new Spiro derivatives of Spiro-OEtTAD, Spiro-OPrTAD, Spiro-OiPrTAD and Spiro-OBuTAD, with the aim to adjust the molecular packing status in perovskite solar cells as hole transporting compounds. Excitedly, with the introduction of ethoxy groups instead of the methoxy ones in Spiro-OMeTAD, Spiro-OEtTAD-based perovskite solar cells demonstrated the highest device performance of 20.16%, higher than that of Spiro-OMeTAD (18.64%).

Funded by

the National Natural Science Foundation of China(21734007,51573140,51673151)

the Natural Science Foundation of Hubei Province(2017CFA002)

and the Fundamental Research Funds for the Central Universities(2042017kf0247,2042018kf0014)


This work was supported by the National Natural Science Foundation of China (21734007, 51573140, 51673151, 21773045), the Natural Science Foundation of Hubei Province (2017CFA002), and the Fundamental Research Funds for the Central Universities (2042017kf0247, 2042018kf0014).

Interest statement

The authors declare that they have no conflict of interest.

Contributions statement

These authors contributed equally to this work.


The supporting information is available online at http://chem.scichina.com and http://link.springer.com/journal/11426. The supporting materials are published as submitted, without typesetting or editing. The responsibility for scientific accuracy and content remains entirely with the authors.


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  • Figure 1

    The molecular design idea and molecular structures of target HTMs (color online).

  • Figure 2

    (a) UV-vis absorption spectra of the Spiro-HTMs in CH2Cl2 solutions. (b) Cyclic voltammograms of Spiro-HTMs in CH2Cl2 solutions. (c) Thermogravimetric analysis curves of Spiro-HTMs under nitrogen at 10 °C min−1 of heating rate. (d) Differential scanning calorimetry of Spiro-HTMs under nitrogen at heating rate of 20 °C min−1 (color online).

  • Figure 3

    The HOMO/LUMO distribution of the Spiro-HTMs (color online).

  • Figure 4

    GIWAXS patterns and the corresponding in-plane and out-of-plane profiles (inset) for pure films of (a) Spiro-OMeTAD. (b) Spiro-OEtTAD. (c) Spiro-OPrTAD. (d) Spiro-OiPrTAD. (e) Spiro-OBuTAD and (f) in-plane line cuts of the Spiro-derivatives (color online).

  • Figure 5

    Device structure of the planar PSCs (a) and energy level diagram of the Spiro-derivatives (b) used in this study (color online).

  • Figure 6

    (a) J-V characteristics of the PSC devices employing Spiro-derivatives as HTMs; (b) IPCE spectra of the PSC devices based on different HTMs; (c) J-V characteristics of Spiro-OEtTAD-based PSCs under different scan conditions (color online).

  • Figure 7

    (a) The J-V curves measured by SCLC characteristic based on single carrier devices. (b) Steady state PL spectra of the perovskite films with or without the capping HTMs. (c) The unencapsulated devices stability test of the devices in ambient (room temperature, 30% RH) (color online).

  • Table 1   The electrochemical, photophysical data of the HTMs and photovoltaic parameters for the PSCs devices based on Spiro-derivatives


    Eg (eV) a)

    EHOMO b)/ELOMO c) (eV)

    λabs,max (nm) d)

    Td (°C) e)

    Tm (°C) f)

    Tg (°C) g)

    Tc (°C) h)





































    Band gaps estimated from the optical absorption band edge of the solution. b) Calculated from the onset oxidation potentials of the compounds. c) Estimated using the empirical equation ELUMO=EHOMO+Eg. d) Values derived from absorption spectra in dilute CH2Cl2 solution. e) 5% weight loss temperature measured by TGA under N2. f) Melting temperature measured by DSC under N2. g) Glass transition temperature measured by DSC under N2. h) Crystallization temperature measured by DSC under N2.

  • Table 2   The electrochemical, photophysical data of the HTMs and photovoltaic parameters for the PSCs devices based on Spiro-derivatives


    Jsc (mA cm−2)

    Voc (V)

    FF (%)

    PCE (%)

    Calculated Jsc (mA cm−2) a)





    18.64 b) (18.08±0.52) c)






    20.16 (19.75±0.42)






    16.86 (16.73±0.53)






    16.59 (16.50±0.66)






    19.04 (19.47±0.71)


    The integrated current density from the IPCE spectra. b) The best PCE values of the devices. c) The statistical data of the device performance with 20 individual cells.

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