Self-assembled oleamide layer applied for cathode buffer layer of bulk heterojunction solar cells based on PTB7:PC₇₁BM

Abstract

In this work, bulk heterojunction solar cells based on poly[[4,8-bis[(2-ethylhexyl)oxy]benzo[1,2-b:4,5-b′]dithiophene-2,6-diyl][3-fluoro-2-[(2-ethylhexyl)carbonyl]thieno[3,4-b]-thiophenediyl]] and phenyl-C71-butyric-acid-methyl-ester were fabricated using 1,2-dichlolobenzene solutions containing different weight ratios of oleamide. The oleamide layers were self-assembled on the active layer surfaces during the solidification of the active layer after spin coating. A significant increase in open-circuit voltage was observed after the introduction of oleamide at the expense of short-circuit current density. The optimal performance of the solar cell was obtained by spin coating the active layer at 1000 rpm for 60 s using a 1,2-dichlolobenzene solution containing 3% oleamide. The solar cell exhibited a short-circuit current density, an open circuit voltage, a fill factor, and a power conversion efficiency of 13.95 mA/cm2, 0.79 V, 0.47, and 5.22%, respectively. These solar cell behaviors are discussed on the basis of results of morphological analysis by optical microscopy, atomic force microscopy, and surface energy analysis.

Mechanisms for Spontaneous Generation of Interlayers in Organic Solar Cells

“…Two different studies reported the segregation of oleamide, an amphiphilic surfactant, to the BHJ surface during spin coating and corresponding improved device PCE, as shown in Figure and Table . , Furthermore, surface Kelvin Probe measurements indicated that the surface ionization potential of films with oleamide was higher than that of P3HT:PCBM or PTB7:PC 71 BM blends with no additive. The higher ionization potential is associated with a work function reduction of the adjacent Al cathode and improved electron collection.…”

“…Solar cell structure with oleamide interlayer (inset), and current density–voltage ( J – V ) curves of PTB7:PC71BM BHJ with oleamide. Reproduced with permission from ref . Copyright 2016 The Japan Society of Applied Physics.…”