Alcohol-Soluble n-Type Conjugated Polyelectrolyte as Electron Transport Layer for Polymer Solar Cells

Abstract

A novel alcohol-soluble n-type conjugated polyelectrolyte (n-CPE) poly-2,5-bis(2-octyldodecyl)-3,6-bis(thiophen-2-yl)-pyrrolo [3,4-c]pyrrole-1,4-dione-alt-2,5-bis [6-(N,N,N-trimethylammonium)hexyl]-3,6-bis(thiophen-2-yl)-pyrrolo[3,4-c]pyrrole-1,4-dione (PDPPNBr) is synthesized for applications as an electron transport layer (ETL) in an inverted polymer solar cells (PSCs) device. Because of the electron-deficient nature of diketopyrrolopyrrole (DPP) backbone and its planar structure, PDPPNBr is endowed with high conductivity and electron mobility. The interfacial dipole moment created by n-CPE PDPPNBr can substantially reduce the work function of ITO and induce a better energy alignment in the device, facilitating electron extraction and decreasing exctions recombination at active layer/cathode interface. As a result, the power conversion efficiency (PCE) of the inverted devices based poly(3-hexylthiophene) (P3HT):(6,6)-phenyl-C 61 butyric acid methyl ester (PC 61 BM) active layer with PDPPNBr as ETL achieves a value of 4.03%, with 25% improvement than that of the control device with ZnO ETL. Moreover, the universal PDPPNBr ETL also delivers a notable PCE of 8.02% in the devices based on polythieno[3,4-b]-thiophene-co-benzodithiophene (PTB7):(6,6)-phenyl-C 71 -butyric acid methyl ester (PC 71 BM). To our best knowledge, this is the first time that n-type conjugated polyelectrolyte-based cathode interlayer is reported. Quite different from the traditional p-type conjugated and nonconjugated polyelectrolytes ETLs, n-CPE PDPPNBr as ETL could function efficiently with a thickness approximate 30 nm because of the high conductivity and electron mobility. Furthermore, the PDPPNBr interlayer also can ensure the device with the improved long-term stability. The successful application of this alcohol solution processed n-type conjugated polyelectrolyte indicates that the electron-deficient planar structure with high electron mobility could be very promising in developing high performance and environmentally friendly polymer solar cells.

Achieving an Efficiency Exceeding 10% for Fullerene‐based Polymer Solar Cells Employing a Thick Active Layer via Tuning Molecular Weight

“…The dependence of J sc on light intensity ( P light ) of these polymers with different M n s under different thickness of active layer was also measured, as shown in Figure b and Figure S2 in the Supporting Information. The relationship between J sc and P light can be described by the power‐law equation: J sc ∝ P light α . If all the charges are swept out and collected by the electrode before recombination, the calculated α value should be 1, while α < 1 hints the existence of charge recombination.…”

“…The relationship between J sc and P light can be described by the power-law equation: J sc ∝P light α . [40] If all the charges are swept out and collected by the electrode before recombination, the calculated α value should be 1, while α < 1 hints the existence of charge recombination. According to the fitting results, the optimal device with M n s of 12, 23, 31, and 38 kDa exhibited α values of 0.914, 0.927, 0.943, and 0.941, respectively, which suggests that the bimolecular recombination gradually becomes weaker in the device with the increased M n .…”

High‐Performance Additive‐/Post‐Treatment‐Free Nonfullerene Polymer Solar Cells via Tuning Molecular Weight of Conjugated Polymers

“…The device based on 12, 23, 31, and 38 kD PBTIBDTT‐S showed a growing P diss value of 89.2%, 91.5%, 93.3%, and 93.6%, respectively, which proves the continually improved exciton dissociation and charge collection properties. The dependence of J sc on light intensity ( P light ) was plotted on a log–log scale and fitted to a power law following the equation of J sc ∝ P light α , as shown in Figure b . If all the charges are swept out and collected by the electrode before recombination, the calculated α value should be 1, while α < 1 hints the existence of charge recombination.…”

2D Conjugated Polyelectrolytes Possessing Identical Backbone with Active‐Layer Polymer as Cathode Interlayer for Organic Solar Cells

“…Typical examples are polyfluorene derivatives like PFN, PFNBr, and PFPN‐Br,4,23–25 which as the CIL remarkably improve the device performance. Besides, more quaternary ammonium‐containing CPEs with n‐type conjugated backbones such as diketopyrrolopyrrole and naphthalene diimide have also been reported as the CIL for high‐performance PSCs 26,27…”