Transform of Work Function of Poor-solvent Induced Active Layer Surface in All-polymer Solar Cells†

doi:10.7503/cjcu20170502

Abstract

Abstract:

The binary of blend poly{4,8-bis[5-(2-ethylhexyl)thiophen-2-yl]benzo[1,2-b∶4,5-b']dithiophe-ne-alt-3-flu-orothieno[3,4-b]thiophene-2-carboxy-late}(PTB7-Th)∶poly{[N,N-bis(2-octyldodecyl)-napthalene-1,4,5,8-bis(dicarboximide)-2,6-diyl]-alt-5,5'-(2,2'-bithiophene)}(N2200)(PTB7-Th∶N2200) active layer films were annealed by methanol solvent. The difference of contact potential between active layer and gold-coated tip were increased from 37 mV to 160 mV, which means the surface work function decreased from 4.71 eV to 4.59 eV. XPS result showed that more N2200 diffused to surface of active layer during vapor annealing because there was a stronger interaction between poor polar solvent methanol and N2200. Such diffusion lead to the decrease of work function which was beneficial to promote energy match between electrode and active layer and the formation of better ohmic contact, which resulted in the over 10% enhance of power conversion efficiency of corresponding organic solar cells.

Key words: All-polymer solar cell, Solvent annealing, Work function of active layer surface, Diffuse

CLC Number:

O646
O641

TrendMD:

LI Hongai, SONG Chunpeng, QU Yi, ZHANG Jidong. Transform of Work Function of Poor-solvent Induced Active Layer Surface in All-polymer Solar Cells^†[J]. Chem. J. Chinese Universities, 2018, 39(2): 263.

Figures/Tables 7

Scheme 1 Chemical structures of the Donor(PTB7-Th) and Acceptor(N2200) polymers

Fig.1 Contact potential difference(CPD) images of the active layer with methanol solvent vapor annealing different time obtained from KPFM t/min: (A) 0; (B) 1; (C) 2; (D) 3.

Fig.2 Surface topographic AFM images with methanol annealing t/min: (A) 0; (B) 1; (C) 2.

Fig.3 XPS spectra for element F1s(A) and N1s(B) of active layers with methanol solvent vapor annealing t/min: a. 0; b. 1; c. 2.

Fig.4 Vis-NIR absorption spectra(A) and XRD pattern(B) of the crystallization of PTB7-Th∶N2200 in films vapor annealing by methanol

Fig.5 Conventional N2200∶PTB7-Th organic bulk-heterojunction solar cells device stack(A) and current density-voltage characteristics of polymer solar cells(PSC) devices with methanol solvents treatment under 100 mW/cm AM 1.5G solar illumination based on PTB7-Th∶N2200 active layer(B)t/min: a. 0; b. 1; c. 2.

Table 1 Photovoltaic parameters of the PTB7-Th∶N2200 based solar cells measured under 100 mW/cm2 AM 1.5G solar illumination

Annealing time/min	V_oc/V	J_sc/(mA·cm^-2)	FF(%)	PCE(%)
0	0.78	8.94	0.50	3.51
1	0.80	9.56	0.51	3.89
2	0.80	9.86	0.50	3.97

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