Large-area thin film deposition technologies for fabricating hybrid perovskite solar cells

Abstract

Organic-inorganic hybrid perovskite solar cells have attracted tremendous research interests due to their amazing light to electric power conversion efficiencies (PCEs). In the past four years, the PCE of perovskite solar cells has significantly increased up to 22.1%, which outperforms several other types of third-generation solar cells and becomes the most promising candidate to compete with the traditional silicon-based solar cells. This result is mainly owing to some excellent properties of the hybrid perovskite active layer, such as a high absorption coefficient, an appropriate band gap and a long carrier diffusion length. Nevertheless, most of the reported high efficiencies were only achieved with very small active areas in the range of 0.03 to 0.2cm2, which is likely to cause measurement errors. What is worse, the material utilization ratio is only 1% during film deposition, hindering the industrial production of perovskite solar cells in the future. Therefore, a large-scale production process has become a big challenge to realize the purpose of commercial applications. To date, the best certified PCE of 19.6% has been obtained with an active area exceeding 1cm2. The most important aspect is fabricating large-area uniform, pinhole-free and large crystal grain perovskite thin films for scaling up high PCE perovskite solar cells. To realize the purpose of large-area, high-quality perovskite film fabrication, a range of thin film fabrication techniques have been proposed, including spin-coating, vacuum flash-assisted solution process (VASP), doctor blading, slot-die coating, inkjet printing, spray coating, vapor assisted deposition and soft-cover deposition. This review aims at giving an overview of these thin film deposition techniques for the processing of perovskite thin film fabrication. By comparing the film quality and material utilization ratio corresponding to different film deposition methods, the studies on perovskite thin film fabrication techniques are summarized. Among these techniques, spin-coating has been widely used in laboratory for perovskite film fabrication, but the material utilization ratio is usually less than 1%, hindering the fabrication of perovskite film with large-area. Spin-coating combined with VASP exhibits an amazing result for high-quality perovskite film fabrication, but it still has a low material utilization ratio in spin-coating process. Other techniques, like doctor blading, slot-die coating and inkjet printing are suitable for large-area perovskite film fabrication with high material utilization ratio. Spray coating and soft-cover deposition also have shown great potential for large-area perovskite film fabrication. The PCEs of perovskite solar cells have reached 13% and 17% with an active area exceeding 1cm2, respectively. Particularly, a high-quality perovskite film with a large-area of 51cm2 was obtained by soft-cover deposition, which made this technique more promising for the development of perovskite solar cells in the future. Based on this review, we suggest that VASP is a suitable technique for depositing high-quality large-area perovskite film. It would be a promising technique to combine VSAP with other techniques, such as doctor blading, inkjet printing, etc., to enhance material utilization ratio for large-scale perovskite solar cells. In addition, some simpler and lower-cost techniques should be developed for the fabrication of perovskite solar cells in the future.