Improving the Photovoltaic Performance and Mechanical Stability of Flexible All-Polymer Solar Cells via Tailoring Intermolecular Interactions

Abstract

Naphthalene diimide (NDI)-based copolymers are promising polymer acceptors in all-polymer solar cells (all-PSCs), but their large crystal domains cause large-scale phase separation in all-polymer blend films. This limits the photovoltaic performance and mechanical stability of all-PSCs. Herein, we control all-polymer blend films by introducing a fluorinated copolymer of NDI and (E)-1,2-bis(3fluorothiophen-2-yl)ethene (FTVT) (PNDI−FTVT) as a polymer acceptor for flexible all-PSCs. The copolymer PNDI−FTVT has a less crystalline structure and higher electron mobility than its nonfluorinated copolymer counterpart (PNDI− TVT). A blended film incorporating PNDI−FTVT exhibits a well-mixed morphology and improves the chain interconnectivity with a polymer donor, providing better charge transport pathways and enhanced mechanical resilience. The PNDI−FTVTbased flexible all-PSC exhibits enhanced photovoltaic performance in comparison with a PNDI−TVT-based flexible all-PSC (5.11−7.14%) as well as excellent mechanical stability in a flexible all-PSC (7.14−5.78%), maintaining 81% of its initial performance at a bending radius of 8.0 mm after 1000 bending cycles.

High‐Performance All‐Polymer Solar Cells with a Pseudo‐Bilayer Configuration Enabled by a Stepwise Optimization Strategy

“…[ 3,6,20–22 ] However, some major problems, related to the blend morphologies of P D s and P A s, namely the bulk heterojunction (BHJ), which is generally formed during P D ‐ P A mixture solution casting, have been identified in all‐PSCs, including large‐scale demixing of P D / P A domains, [ 8,21 ] unoptimized P D / P A ordering, [ 23,24 ] and misaligned molecular orientation at P D ‐ P A interfaces. [ 25,26 ] Thus, reasonable use of different morphology control strategies, such as modification of molecular structures, [ 5,9,21,27 ] selection of solvent and additive, [ 6,20,28 ] thermal annealing, [ 6,22 ] and so on, to modify domain size and phase purity in all‐PSCs is critical. For instance, various random ternary copolymerization strategies were purposed to design P A derivatives, including naphthalene diimide (NDI)‐based N2200 derivatives (PNDI‐CBS 0.5 and BSS10), [ 21,29 ] and Y6‐like PSMAs (PTPBT‐ET 0.3 and PYE 0.2 ), [ 14,30 ] etc., for improving effectively phase‐separated BHJ morphologies.…”

High‐Performance All‐Polymer Solar Cells Enabled by n‐Type Polymers with an Ultranarrow Bandgap Down to 1.28 eV

“…As compared to other types of OSCs, allpolymer solar cells (all-PSCs), comprised of a p-type polymer as electron donor and an n-type polymer as electron acceptor in bulk heterojunction (BHJ) blend film, show several pronounced advantages, including superior mechanical flexibility/stretchability and improved device stability. [15][16][17][18][19] However, the PCEs of all-PSCs lag greatly behind OSCs based on wide bandgap polymer donors and narrow bandgap non-fullerene small molecule acceptors till now, which are mainly restricted by the weak and limited absorption of all-polymer blends in the near-infrared region (NIR). [20][21][22][23][24][25] Although enormous research efforts have been dedicated to developing high-performance polymer acceptors, [16,[26][27][28] very few can yield a PCE > 8% in all-PSCs and among them the acceptors with bandgap smaller than 1.3 eV have never been realized.…”

Strategic Halogen Substitution to Enable High‐Performance Small‐Molecule‐Based Tandem Solar Cell with over 15% Efficiency

“…In addition, the true paracrystal sizes ( L T ) of the BDTID‐X were calculated via a Hosemann plot to understand the charge transport associated with the crystallites of the BDTID‐X (Figure 4c). [ 41–43 ] The detailed explanation of Hosemann Plot is described in the Experimental Section. The L T values of the BDTID‐F, BDTID‐Cl, and BDTID‐Br were 162, 154, and 177 Å, respectively.…”