Morphology Optimization via Side Chain Engineering Enables All-Polymer Solar Cells with Excellent Fill Factor and Stability

Abstract

All-polymer solar cells (all-PSCs) composed of conjugated polymers as both donor and acceptor components in bulk heterojunction photoactive layers have attracted increasing attention. However, it is a big challenge to achieve optimal morphology in polymer:polymer blends. In response, we report herein a new strategy to adjust the nanoscale organization for all-PSCs. Specifically, side chain engineering of the well-known naphthalene diimide (NDI)-based polymer N2200 is modulated by introducing a fraction of linear oligoethylene oxide (OE) side chains to replace branched alkyl chains on the NDI units and by synthesizing a series of NDI-based polymer acceptors NOE x, where x is the percentage of OE chain substituted NDI units relative to total NDI units. Compared to the reference polymer NOE0, OE-chain-containing polymer NOE10 offers a much higher power conversion efficiency (PCE) of 8.1% with a record high fill factor (FF) of 0.75 in all-PSCs. Moreover, the NOE10-based all-PSC exhibits excellent long-term and thermal stabilities with >97% of the initial PCE being maintained after 300 h of aging at 65 °C. This work demonstrates an effective morphology optimization strategy to achieve highly efficient and stable all-PSCs and shows the excellent potential of NOE10 as an alternative to commercially available acceptor polymers N2200.

Rational Strategy to Stabilize an Unstable High‐Efficiency Binary Nonfullerene Organic Solar Cells with a Third Component

“…2019, 9,1900376 techniques at the Advanced Light Source, Lawrence Berkeley National Laboratory. To have a complete picture of the blend morphology, the nanoscale packing, mesoscale spacing, and compositional variation of the blend films were characterized with X-ray based Adv.…”

“…The R-SoXS profiles of the fresh and aged samples exhibit lognormal distribution as shown in Figure 4d with slight differences in the background. 2019, 9,1900376 related to the production, recombination and collection of charges in operational solar cells. The long period of the fresh sample is found to be 38 nm, which slightly increases to 43 nm for the aged sample, indicating a slight change in domain size.…”

“…The ternary devices with 15 wt% PC 71 BM (IEICO-4F:PC 71 BM = 85:15) maintain more than 90% of the initial PCE after storing in the dark in a glove box for 90 days (Figure 6a). 2019, 9,1900376 of the ternary devices rules out the degradation of interlayers and electrodes as a factor for performance degradation of the PTB7-Th:IEICO-4F binary devices. The improved stability of the ternary devices mainly results from the robust FF of the aged devices.…”

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decades, heuristic approaches have been successfully used to enhance the performance of OSCs, including synthesis of new donor and acceptor molecules, [5][6][7][8][9][10] optimization of the interface and morphology, [11][12][13][14][15] ternary blending, [16][17][18][19] and device engineering. [20][21][22][23] As a result, power conversion efficiency (PCE) of OSCs has surpassed 15% for single-layer bulkheterojunction systems.

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“…2019, 9,1900376 Figure 1. a) Illustration of the effective Flory-Huggins interaction parameter (χ)-volume composition of acceptor (φ) phase diagram. Energy Mater.…”