Improved Mechanical Durability of High‐Performance OPVs Using Semi‐Interpenetrating Networks

Organic photovoltaic (OPV) devices offer a number of unique advantages over conventional single crystal silicon solar cells, such as simple and low-cost fabrication, significantly reduced weight, high flexibility, and semitransparency. However, OPV devices exhibit poor durability to mechanical deformations. Here, the use of an elastic semi-interpenetrating network is studied to improve the mechanical durability of the active layer of OPV devices based on the high-performance poly[(2,6-(4,8-bis(5-(2-ethylhexyl-3-fluoro)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)]:2,2 '-[[6,6,12,12-tetrakis(4-hexylphenyl)-6,12-dihydrodithieno[2,3-d:2 ',3 '-d ']-s-indaceno[1,2-b:5,6-b ']dithiophene-2,8-diyl]bis[methylidyne(3-oxo-1H-indene-2,1(3H)-diylidene)]]bis[propanedinitrile] donor:acceptor blend (PBDBT-2F:ITIC). The elastic interpenetrating network is synthesized in situ through the UV photoinitiated crosslinking of thiol-ene additives in the active layer. The effects of strain as a function of bending on the network-stabilized active layer structure are systematically investigated. The elastic interpenetrating network suppresses crack formation and improves durability to high-curvature and repeated bending deformations. Performance measurements show that network-stabilized devices outperform pristine devices above a critical bending strain and number of bending deformations. The photovoltaic performance in general decreases with the increase in the network content, and the best performing devices are obtained using network forming reagents that are most compatible with the donor:acceptor system. This work describes an effective route to flexible devices using semi-interpenetrating polymer networks and provides insight into the design of the networks to maximize photovoltaic performance.