Lightweight and ultra-flexible perovskite solar cells with 'sandwich' perovskite layer based on graphene-carbon nanotube electrodes

Flexible perovskite solar cells (FPSCs) have fired widespread research enthusiasm due to their great potential in the booming field of flexible electronics and portable devices. A lot of research has been conducted on the performance, flexibility, and stability of FPSCs, but the synergistic improvement between them is still terribly difficult. In this work, we have achieved the lightweight and ultra-flexible perovskite solar cell (LWUF PSC) with high performance and remarkable stability. Specifically, in addition to using a 1.5 µm-thick polyetherimide film as flexible substrate, the improved scheme mainly includes designing a "sandwich" architecture with multifunctionality to take advantage of perovskite quantum dots and polycrystalline perovskite, employing a flexible electrode of graphene-carbon nanotube film, and a hole transport layer of CuCrO₂ nanoparticles containing nickel to facilitate the transfer of photogenerated charge carriers. The resultant device demonstrates a stable power conversion efficiency (PCE) of 17.4% and a power-per-weight of 31.1 W g^-1. In particular, after 10,000 bending cycles with a curvature radius of 1 mm, the PCE of the LWUF PSC has sustained at 92.8% of its initial level, and after 32 days in an atmosphere with a relative humidity of 35%, it has remained at 93.0% of its initial level. The unique device’s structure design gives the LWUF PSC high PCE, significant power-per-weight, excellent mechanical flexibility and outstanding environmental stability – one of the best performance to date of LWUF PSCs without indium tin oxide electrodes.