Composite Interlayer Consisting of Alcohol-Soluble Polyfluorene and Carbon Nanotubes for Efficient Polymer Solar Cells

Abstract

We report the synthesis of composite interlayers using alcohol-soluble polyfluorene (ASP)-wrapped single-walled carbon nanotubes (SWNTs) and their application as electron-transport layers for efficient organic solar cells. The ASP enables the individual dispersion of SWNTs in solution. The ASP-wrapped SWNT solutions are stable for 54 days without any aggregation or precipitation, indicating their very high dispersion stability. Using the ASP-wrapped SWNTs as a cathode interlayer on zinc oxide nanoparticles (ZnO NPs), a power conversion efficiency of 9.45% is obtained in PTB7-th:PC71BM-based organic solar cells, which is mainly attributed to the improvement in the short circuit current. Performance enhancements of 18 and 17% are achieved compared to those of pure ZnO NPs and ASP on ZnO NPs, respectively. In addition, the composite interlayer is applied to non-fullerene-based photovoltaics with PM6:Y6, resulting in a power conversion efficiency of up to 14.37%. The type of SWNT (e.g., in terms of diameter range and length) is not critical to the improvement in the charge-transport properties. A low density of SWNTs in the film (∼1 SWNTs/μm2 for ASP-wrapped SWNTs) has a significant influence on the charge transport in solar cells. The improvement in the performance of the solar cell is attributed to the increased internal quantum efficiency, balanced mobility between electrons and holes, and minimized charge recombination.

Nonpolar Solvent‐Dispersible Alkylated Reduced Graphene Oxide for Hole Transport Material in n‐i‐p Perovskite Solar Cells

“…The lower R sh of AF‐rGO, which could be attributed to high electrical conductivity in parallel direction arising from the 2D nature of the AF‐rGO, may be one of the primary reasons for the lower FF in the PeSC, which consequently generated a slightly lower PCE. [ 37 ] However, the PCE of 17% with the AF‐rGO is the highest PCE of n‐i‐p PeSCs using graphene‐based materials as the sole HTM to date (Figure 4b). [ 25,38–41 ] We summarize the photovoltaic performance of an n‐i‐p‐structured PeSC with graphene‐based HTMs in Table S3, Supporting Information.…”

Recent Applications of Carbon Nanotubes in Organic Solar Cells

“…The photovoltaic parameters of OSCs with CNT-based ETLs, discussed in this study, are summarized in Table 4 . From these, the highest PCE of 14.37% was achieved by OSCs with the ZnO:ASP-SWCNTs ETL ( Lee et al, 2020 ), demonstrating the suitability of CNT-based ETLs in the fabrication of highly efficient devices.…”

“…Recently, alcohol-soluble polyfluorene (ASP)-wrapped SWCNTs have been incorporated into ZnO NPs and employed as composite ETLs in OSCs ( Lee et al, 2020 ). ASP facilitated the individual dispersion of SWCNTs in solution, which resulted in smooth films with low R rms as shown in Figure 11 , thereby addressing the issue of leakage current due to short-circuits, originating from the agglomeration and bundling of poorly dispersed SWCNTs in rough films.…”

“… AFM micrographs of (A) pristine ZnO NPs and (B) ASP-SWCNTs on ZnO NPs. Adapted with permission ( Lee et al, 2020 ). Copyright 2020, American Chemical Society.…”

A pH‐Neutral Polyelectrolyte Hole Transport Layer for Improved Energy Band Structure at the Anode/PTB7 Junction and Improved Solar Cell Performance

“…[ 8–11 ] Recently reported research has focused on developing new interlayer materials with stable physical properties and adequate energy levels between the interfaces to increase charge selectivity at the corresponding electrode and prevent undesirable charge recombination. [ 12–15 ]…”