Side Chain Engineered Naphthalene Diimide-Based Terpolymer for Efficient and Mechanically Robust All-Polymer Solar Cells

Abstract

The recent evolution of new polymer acceptors (P A s) using small-molecule building blocks with high light absorption has significantly increased the power conversion efficiency (PCE) of all-polymer solar cells (all-PSCs), but their mechanical properties are typically poor. Thus, poly[[N,N′-bis(2octyldodecyl)-naphthalene-1,4,5,8-bis(dicarboximide)-2,6-diyl]alt-5,5′-(2,2′-bithiophene)] (N2200) is still considered one of the most successful P A s in all-PSCs. Herein, we report the development of new naphthalene dimide-based P A s (NDI-P A s) that enable the achievement of both superior PCEs and mechanical robustness of all-PSCs compared to those of N2200-based devices. Our approach is very simple and effective for constructing a series of P A s [PNDIHD/DT-x, where x = 0−1], consisting of two NDI units with different side chains (2-hexyldecyl (HD) and 2decyltetradecyl (DT)). The PNDIHD/DT-0.41-based all-PSCs with the poly [(2,6-(4,8-bis(5-(2-ethylhexyl)thiophen-2-yl)benzo[1,2-b:4,5-b′]dithiophene))-alt-(5,5-(1′,3′-di-2-thienyl-5′,7′-bis(2-ethylhexyl)benzo[1′,2′-c:4′,5′-c′]dithiophene-4,8-dione))] (PBDB-T) polymer donor achieve a PCE of 9.3%, which outperforms the N2200-based device (PCE = 7.7%). This is mainly attributed to the enhanced charge generation and transport abilities of the PNDIHD/DT-0.41-based all-PSCs, as a result of optimal domain size and purity as well as high electron mobility. Importantly, the PBDB-T:PNDIHD/DT-0.41 blend shows excellent mechanical robustness, with a crack onset strain (COS) of 30% and a toughness of 7.5 MJ m −3 . In addition, a flexible polymer solar cell (FPSC) device with the PBDB-T:PNDIHD/DT-0.41 blend shows a high initial PCE of 6.73%, which is maintained over 6% even after bending 1500 times.

Polymer Acceptors with Flexible Spacers Afford Efficient and Mechanically Robust All‐Polymer Solar Cells

“…To investigate the P A aggregation property depending on the FCBS unit content, the temperature‐dependent UV–vis absorption spectra in CB solution were measured (Figure S3, Supporting Information). [ 28,47–50 ] PYTS‐0.0, PYTS‐0.1, and PYTS‐0.3 exhibited blueshifted absorption maxima and gradually decreased absorption intensity as temperature increased, which indicates that the P A s tend to being aggregated at room temperature, but being disaggregated at high temperatures. [ 51 ] However, PYTS‐0.0 has the lowest solubility and merely soluble even in hot CB solution (Figure S2 and Table S1, Supporting Information).…”

High-Molecular-Weight Electroactive Polymer Additives for Simultaneous Enhancement of Photovoltaic Efficiency and Mechanical Robustness in High-Performance Polymer Solar Cells

“…Notably, the scattering peaks got more distinct and sharper with increasing P A content, suggesting gradational development of independent phases of the blend components. 70 For a more quantitative analysis, we estimated the relative domain purity of each blend, which is proportional to the square root of the integrated scattering intensity (√ISI) ( Table S7 ). 71 To note, the addition of 10 wt % of the P A increased the relative domain purity to 0.20.…”

Tailoring polymer acceptors by electron linkers for achieving efficient and stable all-polymer solar cells

“…As with the above-discussed optical properties, the crystalline correlation lengths (CCLs) of these three P A s also exhibit a linear increase (CCL PY-O = 16.71 Å, CCL PY-S = 18.05 Å, CCL PY-Se = 18.42 Å) according to the sequential chalcogen elements. This result reflects the crystallinity behaviors of the neat P A films and the strength of intermolecular interactions in the solid-state and also implies their charge transport properties [ 43 , 44 ]. Thus, the electron mobilities of the neat P A s films were further measured using the space-charge-limited-current (SCLC) method (Fig.…”