Influence of Acceptor Type and Polymer Molecular Weight on the Mechanical Properties of Polymer Solar Cells

Abstract

Nonfullerene acceptors (NFAs), that are smallmolecule acceptors (SMA) and polymer acceptors (PAs), have been extensively explored, which has yielded significant enhancements in the photovoltaic performance of polymer solar cells (PSCs). The mechanical robustness of the PSCs is of vital and equal importance to ensure long-term stability and enable their use as power-generators in flexible and stretchable electronics. Here, we report a comparative study of the mechanical properties of SMA-based, PA-based, and fullerenebased PSCs. We chose ITIC (SMA), P(NDI2OD-T2) (PA), and PCBM (fullerene) as three representative acceptor materials and blended them with the same polymer donor PTB7-Th. To understand the difference between the mechanical properties of SMA-based and PA-based PSCs, we control the number-average molecular weight (M n ) of P(NDI2OD-T2) from 15 to 163 kg mol −1 in all-PSCs. The all-PSCs-based high-M n PAs exhibit significantly higher cohesion energy (4.03 J m −2 ) than SMA-PSCs (1.19 J m −2 ) and PCBM-PSCs (0.29 J m −2 ). Notably, the all-PSCs exhibit a high strain at fracture of 31.1%, which is 9-and 28-fold higher than those of SMA-PSCs and PCBM-PSCs, respectively. The superior mechanical robustness of all-PSCs is attributed to using a PA above the critical molecular weight (M c ), which produces tie molecules and polymer entanglements that dissipate substantial mechanical strain energy with large plastic deformation. This work provides useful design guidelines for photovoltaic active materials in terms of the mechanical properties and highlights the importance of incorporating high-M n PAs above the M c for producing PSCs with excellent mechanical robustness and device performance.

Highly efficient, heat dissipating, stretchable organic light-emitting diodes based on a MoO3/Au/MoO3 electrode with encapsulation

“…Similar to the simulation results, the high mechanical reliability of the wrinkled structure in the device was also confirmed by various stability tests. Despite of the strain value of the device (<9%) in simulation, the actual device was not damaged in the stability tests since crack initiation and propagation was prevented by the adhesion of the sticky elastomer substrate [57][58][59] . The simulation result suggests that the geometrically wrinkled structure is suitable to fabricate stretchable OLEDs.…”

Sequential Blade‐Coated Acceptor and Donor Enables Simultaneous Enhancement of Efficiency, Stability, and Mechanical Properties for Organic Solar Cells

“…More importantly, mechanical property of the devices is an indispensable factor for achieving flexible and wearable OSCs . For example, OSCs used as wearable electronics should be able to withstand tensile strain of at least 20–30% . Several reviews have been published on the development of the mechanical property of OSCs, indicating that acceptor type, length of the alkyl side‐chain of polymer, polymer molecular weight, and additive will have an effect on the mechanical property of the device, which provide guidelines for the co‐optimization of both mechanical and photovoltaic properties .…”

Controlling Molecular Mass of Low-Band-Gap Polymer Acceptors for High-Performance All-Polymer Solar Cells

“…Among the various systems in non-fullerene PSCs, 16,17 all-polymer solar cells (all-PSCs), 18 which are composed of binary blends of conjugated polymer donor (P D ) and polymer acceptor (P A ), attract particular interest, because of enhanced polymer electronic structure tunability, excellent thermal stability, and mechanical bulk heterojunction (BHJ) film robustness. [19][20][21] In addition, all-polymer system maintains a good compatibility with large-area manufacture during operation and stress testing protocols. [22][23][24] Recently, the PCEs of all-PSCs have been dramatically enhanced to exceeding 11%.…”