Metal–organic framework nanosheets for enhanced performance of organic photovoltaic cells

Metal–organic framework nanosheets (MONs) are an emerging class of two-dimensional materials whose diverse and readily tunable structures make them ideal for use in optoelectronic applications. Here, liquid exfoliation is used to synthesize ultrathin zinc-porphyrin based MONs with electronic and optical properties ideally suited for incorporation into a polythiophene–fullerene (P3HT–PCBM) organic solar cell. Remarkably, the addition of MONs to the photoactive layer of a photovoltaic device results in a power conversion efficiency of 5.2%, almost twice that for reference devices without nanosheets with a simultaneous improvement of Jsc, Voc and FF. Our analysis indicates that the complimentary electronic, optical and structural properties of the MONs allows them to act as a surface to template the crystallization of P3HT leading to a doubling of the absorbance, a tenfold increase in hole mobility and reduced grain size. These results demonstrate the potential of MONs as a tunable class of two-dimensional materials for enhancing the performance of a broad range of organic solar cells and other electronic devices

High-efficiency spray-coated perovskite solar cells utilizing vacuum-assisted solution processing

We use ultrasonic spray-coating to fabricate cesium-containing triple-cation perovskite solar cells with a power-conversion efficiency of up to 17.8%. Our fabrication route involves a brief exposure of the partially wet spray-cast films to a low vacuum, a process that is used to control film crystallization. We show that films that are not vacuum-exposed are relatively rough and inhomogeneous, while vacuum-exposed films are smooth and consist of small and densely packed perovskite crystals. The process techniques developed here represent a step toward a scalable and industrially compatible manufacturing process capable of creating stable and high-performance perovskite solar cells

High-Performance Multilayer Encapsulation for Perovskite Photovoltaics

An encapsulation system comprising of a UV‐curable epoxy, a solution processed polymer interlayer, and a glass cover‐slip, is used to increase the stability of methylammonium lead triiodide (CH3NH3PbI3) perovskite planar inverted architecture photovoltaic (PV) devices. It is found this encapsulation system acts as an efficient barrier to extrinsic degradation processes (ingress of moisture and oxygen), and that the polymer acts as a barrier that protects the PV device from the epoxy before it is fully cured. This results in devices that maintain 80% of their initial power conversion efficiency after 1000 h of AM1.5 irradiation. Such devices are used as a benchmark and are compared with devices having initially enhanced efficiency as a result of a solvent annealing process. It is found that such solvent‐annealed devices undergo enhanced burn‐in and have a reduced long‐term efficiency, a result demonstrating that initially enhanced device efficiency does not necessarily result in long‐term stability