High-efficiency ultrathin flexible organic solar cells with a bilayer hole transport layer

Abstract

The storage stability and mechanical durability are two key parameters for the application of flexible organic solar cells (OSCs), which are considered a promising power source for wearable electronics. However, most of the high-efficiency flexible OSCs are fabricated based on the poly(3,4-ethylenedioxythiophene):poly(styrene–sulfonate) (PEDOT:PSS) hole transport layer, which hinders the long-term operation, especially under cyclic bending or stretching. Herein, we develop an ultrathin flexible OSC (with a total thickness of less than 1.5 μm) based on the bilayer hole transport layer, incorporating a MoO₃ interlayer between PEDOT:PSS and ITO, which can simultaneously improve the efficiency, storage stability and mechanical stability of ultrathin flexible OSCs. The ultrathin OSC based on the bilayer HTL achieves a power conversion efficiency (PCE) of 17.0% and a power-per-weight ratio of 39.3 W g⁻¹, compared to single-layer HTL devices with a PCE of 16.4%. To the best of our knowledge, this is one of the highest efficiencies among all ITO-based ultrathin OSCs. Furthermore, the best-performing ultrathin OSCs show PCE retentions of 89.1% and 84.4% after 1000 cycles of bending (with a bending radius of 1 mm) and 1000 cycles of compression–stretching tests, respectively.