A highly flexible and durable transparent graphene electrode with thermal stability was developed via the direct integration of polyimide (PI) on graphene. Due to the high transparency of PI-integrated graphene electrode and intimate contact between graphene and PI substrate, high-efficiency flexible organic solar cell with a PCE of 15.2% and outstanding mechanical robustness was obtained.

Metal-based transparent conductive electrodes (TCEs) are attractive candidates for application in indium tin oxide (ITO)-free solar cells due to their excellent electrical conductivity and cost effectiveness. In perovskite solar cells (PSCs), metal-induced degradation with the perovskite layer leads to various detrimental effects, deteriorating the device performance and stability. Here, we introduce a novel flexible hybrid TCE consisting of a Cu grid-embedded polyimide film and a graphene capping layer, named GCEP, which exhibits excellent mechanical and chemical stability as well as desirable optoelectrical properties. We demonstrated the critical role of graphene as a protection layer to prevent metal-induced degradation and halide diffusion between the electrode and perovskite layer; the performance of the flexible PSCs fabricated with GCEP was comparable to that of their rigid ITO-based counterparts and also exhibited outstanding mechanical and chemical stability. This work provides an effective strategy to design mechanically and chemically robust ITO-free metal-assisted TCE platforms in PSCs.

exceeds 25% for the conventional structure. [5] The inverted structured PSCs also show great promises with advantages such as low-temperature processability and ionic dopant-free hole transport layer, which can contribute toward fabricating flexible devices or improving the operational stability. [6-14] Recently, Zheng et al. reported stable inverted PSCs exhibiting a PCE of 23.0%. [15] Meng et al. demonstrated a highly flexible inverted PSCs with a PCE of 19.9%. [16] Despite such rapid progresses in PSCs, the stability of perovskite still remains below commercialization standards, because perovskite is inherently unstable under ambient environmental conditions such as ultraviolet (UV) irradiation, and is particularly degraded by humidity and heat. Perovskite is hydrophilic, meaning that moistures can readily infiltrate along the grain boundaries of its crystals, triggering severe decomposition of the constituent elements and a consequent decline in device performance. [17,18] In addition, the constituent atomic species of perovskite materials are thermally decomposed at elevated temperatures, even under protective encapsulation layers. The decomposed organic and halide ions preferentially migrate along the grain boundaries of the perovskite crystals and into the adjacent charge transporting layers, or even into the metal electrodes of the solar cell. These behaviors readily lead to defect states (e.g., cations and halide vacancies) and metal halide formations, which severely degrade the device performance. [19,20] Moreover, the unfavorable volume expansion of the perovskite lattice under continuous thermal stresses accelerates the moisture diffusion, further deteriorating the quality of perovskite film. [21] Thus, improving the stability of PSCs in moist and thermally elevated environments is greatly demanded. Defects in perovskite crystals, such as the vacancies of perovskite constituent, grain boundaries, and uncoordinated Pb 2+ ions, become the source of nonradiative recombination centers, which can adversely affect the device performance of PSCs as well as the operational stability. However, pristine perovskite films are typically known to be quite vulnerable to intrinsic defect generation. [22,23] Therefore, to minimize the defect formation and thus achieve high-quality perovskite layers with large grain size and uniform surface morphology, researchers have added cations or anions, applied antisolvent treatments, and modified neighboring layers. [24,25] Chemical additives have Significant efforts have been devoted to modulating the grain size and improving the film quality of perovskite in perovskite solar cells (PSCs). Adding materials to the perovskite is especially promising for high-performance PSCs, because the additives effectively control the crystal structure. Although the additive engineering approach has substantially boosted the efficiency of PSCs, instability of the perovskite film has remained a primary bottleneck for the commercialization of PSCs. Herein, a newly conceived bithiophene-based n-...

Two-dimensional Ruddlesden–Popper (RP) phase perovskite is gaining increasing attention for passivating the defects of the bulk absorber layer in perovskite solar cells (PSCs). However, owing to its anisotropic structural features,...

Flexible semitransparent perovskite solar cells (ST-PSCs) have great potential for use in high-density energy systems, such as building or vehicle integrated photovoltaics, considering the great features of PSC devices, including high performance, light weight, thin-film processability, and high near-infrared transmittance. Despite numerous efforts toward achieving efficiency and flexibility in ST-PSCs, the realization of high-performance and operational stability in ST-PSCs still require further development. Herein, we demonstrated the development of highly efficient, stable, and flexible ST-PSCs using polyimide-integrated graphene electrodes via a lamination-assisted bifacial cation exchange strategy. A high-quality perovskite layer was obtained through the cation exchange reaction using the lamination process, and ST-PSCs with 15.1% efficiency were developed. The proposed ST-PSC device also demonstrated excellent operational stability, mechanical durability, and moisture stability owing to the chemically inert and mechanically robust graphene electrodes. This study provides an effective strategy for developing highly functional ST-perovskite optoelectronic devices with high-performance and long-term operational stability.