Network-Stabilized Bulk Heterojunction Organic Photovoltaics

Abstract

Bulk heterojunction organic photovoltaic (OPV) devices are multilayer organic devices that can be fabricated using low-cost and scalable solution processing methods, but current devices exhibit poor mechanical stability and degrade under deformation due to cracking and delamination. Recent approaches to improve mechanical durability involve modifying the side-chain or main-chain structures of conjugated polymers in the active layer, but in general it is difficult to simultaneously optimize electronic properties, morphology, and mechanical stability. Here, we present a general approach to improve the mechanical stability of bulk heterojunction active layers through incorporation of an internal elastic network. Network-stabilized bulk heterojunction OPVs are prepared using reactive small molecular additives that are rapidly cross-linked through thiol−ene coupling after processing the active layer. Thiol−ene reactions catalyzed by a base or initiated through short exposure to UV light produce insoluble, elastic thiol−ene networks in the active layer. We show through a combination of crack onset strain measurements, morphological analysis, and OPV device testing that network-stabilized OPVs with up to 20% thiol−ene network exhibit improved deformability with no loss in PCE, and we implement networkstabilized bulk heterojunction OPVs to produce stretchable photovoltaic devices. This work represents a simple approach for improving the mechanical durability of bulk heterojunction OPVs.

Efficient Organic Solar Cells with a High Open‐Circuit Voltage of 1.34 V

“…Bulk heterojunction (BHJ) organic solar cells (OSCs) consisting of electron donor and electron acceptor as light absorbers have attracted broad attention due to their advantages of flexibility, light weight and low cost . Over the last thirty years, great efforts have been made to promote the rapid progress of OSCs, leading to over 17% power conversion efficiencies (PCEs) .…”

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

“…These thiol-ene reagents can be coupled in situ after deposition of the active layer through UV-initiated thiol radical addition or, in the case of DPPA, base-catalyzed thiol Michael addition reactions. [23] In the present study, thiol-ene networks were incorporated into the active layers by spin-casting a solution mixture of thiol-ene reagents along with PBDBT-2F and ITIC. After deposition, the active layer was thermally annealed (120 °C for 30 min) and exposed to UV light (5 min, 254 nm, 1.3 mW cm −2 , UVP Compact UV lamp, model UVGL-25) to crosslink the thiol-ene reagents.…”

“…We previously reported residual film thickness measurements and Fourier transform infrared (FTIR) measurements that confirmed the in situ formation of an interpenetrating network. [23] We first analyzed the impact of the interpenetrating network on the performance of bulk heterojunction OPVs fabricated on rigid ITO glass substrates through measurements of device PCEs. Our primary goal was to compare the performance of a series of devices rather than quantify the absolute PCE, and as such we did not measure external quantum efficiencies (EQEs) for each device.…”

“…We recently reported networkstabilized OPVs and showed that an elastic semi-interpenetrating network formed in the active layer of an P3HT:PCBM OPV enhanced mechanical durability. [23] The elastic network was synthesized using reactive small molecular additives which can form a crosslinked thiol-ene network. The additives were codeposited with the donor and acceptor in the active layer, and the elastic network was generated in situ either through UV-irradiation or base-catalyzed thiol Michael addition coupling.…”

Recent Progress in Flexible and Stretchable Organic Solar Cells

“…Meanwhile, the variation in morphology may attribute to the transitions of the mechanical properties. Unconventionally, Verduzco and co‐workers improved the mechanical robustness of the films though incorporating an internal elastic network, [ 143 ] using reactive small molecular additives to prepare the stretchable OSCs, where additives are rapidly crosslinked through the thiol‐ene coupling. Interestingly, the crack onset strain increased with the increasing concentration of the thiol‐ene.…”