In situ growth of graphene on both sides of a Cu–Ni alloy electrode for perovskite solar cells with improved stability

The instability of rear electrodes undermines the long-term operational durability of efficient perovskite solar cells. Here, a composite electrode of copper–nickel (Cu–Ni) alloy stabilized by in situ grown bifacial graphene is designed. The alloying makes the work function of Cu suitable for regular perovskite solar cells. Cu–Ni is the ideal substrate for preparing high-quality graphene via chemical vapour deposition, which simultaneously protects the device from oxygen, water and reactions between internal components. To rivet the composite electrode with the semi-device, a thermoplastic copolymer is applied as an adhesive layer through hot pressing. The resulting devices achieve power conversion efficiencies of 24.34% and 20.76% (certified 20.86%) with aperture areas of 0.09 and 1.02 cm2, respectively. The devices show improved stability: 97% of their initial efficiency is retained after 1,440 hours of a damp-heat test at 85 °C with a relative humidity of 85%; 95% of their initial efficiency is retained after 5,000 hours at maximum power point tracking under continuous 1 sun illumination. The instability of contact layers for perovskite solar cells under operating conditions limits the deployment of the technology. Now, Lin et al. develop a Cu–Ni electrode sandwiched between in situ-grown graphene protective layers, enabling solar cells with improved stability under light, humidity and high temperature.