Intrinsically‐Stretchable, Efficient Organic Solar Cells Achieved by High‐Molecular‐Weight, Electro‐Active Polymer Acceptor Additives

Abstract

tremendous progress in power conversion efficiency (PCE) and flexibility. [1a,2b,3] Although flexible OSCs exhibit high durability against bending, most of them are not suitable for application in wearable electronics due to the large tensile stress exerted on the devices by human body movements. Specifically, the human body consists of movable joints and elastic skin, which can exert a high stretchability of over 50% strain. [4] Consequently, it is imperative to develop stretchable OSCs beyond the flexible devices reported thus far.Although stretchable OSCs prepared via structural device engineering (i.e., a buckling method) have been reported by a few groups, [5] their manufacturing processes are typically complicated and expensive. Moreover, the stretching is limited to only one allowed direction, and it depends on the pattern of the wrinkled structures. [6] Intrinsically stretchable OSCs (IS-OSCs) have also been developed, utilizing electrodes from organic materials and liquid metal. All the constituent layers in the IS-OSCs can be stretched in every direction, distinguishable from the structurally engineered stretchable devices. [7] For example, Lipomi et al. reported IS-OSCs for the first time consisting of poly(3-hexylthiophene) (P3HT) and phenyl-C 61 -butyric acid methyl ester (PCBM) active layers on stretchable poly(dimethylsiloxane) substrates. [7c] Subsequently, Chen et al. prepared stretchable polymeric charge-transport layers consisting of poly[(9,9-bis(3′-(N,N-dimethylamino) propyl)-2,7-fluorene)-alt-2,7-(9,9-dioctylfluorene)] (PFN) and nitrile butadiene rubber (NBR) to construct IS-OSCs. The resulting device exhibited an initial PCE of 3% and maintained 94% of the performance under a 10% strain. [7a] Recently, we developed IS-OSCs with a higher PCE (≈11%) by using a thermoplastic polyurethane (TPU)-based substrate, a poly(3,4-ethylened ioxythiophene):poly(styrenesulfonate) (PEDOT:PSS)-based transparent anode, and a liquid metal-based cathode. [7b] Nevertheless, the normalized PCEs of the PM6:Y7-based IS-OSCs rapidly decreased to ≈52% under 15% strain during in situ stretching cycles. [7b] This stretchability falls short of the requirements for practical application as wearable devices on human bodies.The limited stretchability of IS-OSCs is mainly due to the use of a mechanically brittle active layer containing small-molecule acceptors (SMAs). The use of strong light-absorbing SMAs and Organic solar cells (OSCs) are promising wearable/stretchable power sources, but the development of high-performance intrinsically stretchable OSCs (IS-OSCs) has rarely been reported. Herein, IS-OSCs exhibiting high power conversion efficiencies (PCEs) (>12%) and excellent stretchability are developed by constructing efficient and mechanically robust active layers via the addition of a high-molecular weight polymer acceptor (P A ) to polymer donor:smallmolecule acceptor blends. P A addition significantly enhances the stretchability and PCEs of the blends as the long P A chains function as molecular bridges ...

Linker Engineering of Dimerized Small Molecule Acceptors for Highly Efficient and Stable Organic Solar Cells

“…The recent development of Y-family small-molecule acceptors (SMAs) featuring excellent light absorption and charge transport abilities has led to a remarkable increase (>18–19%) in the power conversion efficiency (PCE) of organic solar cells (OSCs), improving the commercial viability of OSC technology. − However, most SMA-based OSCs exhibit poor operational and thermal stability. ,− The poor stability of SMA-based OSCs is mainly associated with the degradation of the optimal bulk-heterojunction (BHJ) morphology of the active layers (polymer donor ( P D ):SMA blends) under external stress, including thermal/mechanical stress and light. − The degradation of the BHJ morphology of P D :SMA blends is accelerated by the rapid diffusion of constituent SMAs due to their low glass transition temperatures ( T g < 100 °C) and high diffusion coefficients ( D > 10 –17 cm 2 s –1 at 85 °C). − …”

Efficient and Nonhalogenated Solvent-Processed Organic Solar Cells Enabled by Conjugated Donor–Acceptor Block Copolymers Containing the Same Benzodithiophene Unit

“…Next, the mechanical properties of PBDB-T- b -PY5BDT and PBDB-T:PY5BDT films were investigated using a pseudo-free-standing tensile test. This method can be used to determine the intrinsic tensile properties of thin films, excluding the effects of underlying thick substrates. − The obtained stress–strain ( S – S ) curves and tensile parameters are presented in Figure c and Table . The PBDB-T:PY5BDT blend film exhibited a crack-onset strain (COS) of 3.8%.…”

Mechanically robust all-polymer solar cells enabled by polymerized small molecule acceptors featuring flexible siloxane-spacers

“…This testing method enables us to obtain the intrinsic tensile properties of thin films, excluding effects from thick substrates. 70–72 All blend films for the tensile testing were prepared under the same conditions as those of device fabrication. The PYSiO-0 blend showed COS and toughness values of 9.6% and 3.2 MJ m −3 , respectively.…”