Tailored lead iodide growth for efficient flexible perovskite solar cells and thin-film tandem devices

Flexible perovskite solar cells (PSCs) hold great promise for the low-cost roll-to-roll production of lightweight single- and multijunction photovoltaic devices. Among the different deposition methods used for the perovskite absorber, the two-step hybrid vacuum-solution approach enables precise control over the thickness and morphology of PbI2. However, efficient conversion to perovskite is limited by diffusion of the organic cations in the compact lead halide layer. Herein, a multistage absorber deposition is developed by thermal evaporation of PbI2 and spin coating of CH3NH3I (MAI). The process relies on the different types of growth of vacuum-deposited PbI2 onto amorphous and crystalline surfaces. This approach represents a way to effectively increase the absorber thickness while tackling the limited MAI diffusion in the compact PbI2 film via a two-step deposition method. The efficiency of flexible PSCs is improved from 14.2 to 15.8% with multistage deposition. Furthermore, the use of an amorphous transparent conductive oxide (TCO), InZnO, enhances the mechanical resistance against bending with respect to conventional crystalline TCO-based flexible devices. Near-infrared transparent flexible PSCs are developed with an efficiency of 14.0% and average transmittance of ~74% between 800 and 1000 nm. Flexible perovskite/CIGS thin-film tandem devices are demonstrated with an efficiency of 19.6% measured in the four-terminal configuration. The efficiency of printable solar cells can be increased using a production method developed by researchers in Switzerland. Hybrid perovskites, a material that combines organic and inorganic components, are emerging as a competitive alternative to silicon for producing solar cells. One of their major advantages is that perovskite devices can be created on flexible substrates, making them compatible with a technology that prints devices on a roll of plastic. This means they can be cheaply mass produced, however their conversion efficiency needs to be improved. Stefano Pisoni and colleagues from the Swiss Federal Laboratories for Materials Science and Technology in Duebendorf constructed a perovskite solar cell using a two-step method that combined thermally evaporated lead iodide and a coating of methylammonium iodide. This design enabled better diffusion of the organic cations, which improved the device efficiency. Flexible perovskite solar cell with an efficiency of 15.8 % via tailoring of vacuum-deposited PbI2 growth morphology has been achieved. We demonstrated superior mechanical bending stability using amorphous TCO (retaining 80 % of the initial efficiency after 1000 bending cycles at 4 mm bending radius). Flexible NIR-transparent perovskite solar cell with an efficiency of 14.0 % and average transmittance of ~74 % between 800 and 1000 nm has been developed. Eventually, we proved a flexible perovskite/CIGS tandem solar cell with an efficiency of 19.6 % measured in four-terminal configuration.