Failure of Stretchable Organic Solar Cells under Monotonic and Cyclic Loading

Abstract

Results of experimental and computational studies of failure of stretchable organic solar cells (SOSCs) are presented here. The SOSCs are produced by the deposition of poly(3,4-ethylenedioxythiophene):polystyrene sulfonate (PEDOT:PSS) anodic layers on prestretched poly(dimethyl-siloxane) (PDMS) substrates. This is followed by the deposition of active organic bulk heterojunction layers and cathodic eutectic gallium indium (EGaIn). Wrinkled structures are then formed by releasing the prestretched PDMS. The underlying failure associated with the formation of the wrinkled films is discussed, along with the subsequent mechanisms of deformation and cracking under monotonic and cyclic loading. Effects of monotonic and cyclic loading on the optical transmittance of the PEDOT:PSS layer and photoconversion efficiencies of the multilayered SOSC structures are also examined. An increase in the transmittance is observed as strain is applied to flatten the wrinkled structures. This enhances the power conversion efficiencies of the SOSCs as the strains increase from 0% to 32%. However, beyond this initial strain regime, the onset of overstretching decreases the optical transmittance and photoconversion efficiencies. The fatigue lifetimes of the layered SOSCs also decrease with increasing fatigue strain ranges between 10% and 25%. The decrease in the fatigue lifetimes is associated with a higher incidence of cracking and delamination.