(604a) Highly Stable Perovskite Solar Cells Fabricated Using Aerosol-Based Technique

Authors: 
Kavadiya, S., Washington University in Saint Louis
Biswas, P., Washington University in St. Louis
Organometallic perovskite (based on CH3NH3PbI3 and its analogues) have attracted substantial attention due to their low-cost synthesis and various applications. Perovskite-based solar cells have shown rapid increase in the efficiency over a short period of time. However, material’s instability under ambient condition is a key challenge for their large-scale applications. Previous studies focused on improving the stability use additives or encapsulation methods and are performed in controlled environment, which restricts the large-scale production of perovskite solar cells. We present a simple, scalable and novel aerosol-based technique, electro-hydro atomization, to fabricate highly stable perovskite solar cells under ambient conditions (room temperature, humidity and atmosphere), without use of any additives or encapsulation. A two-step deposition method is used to form the perovskite layer, where PbI2 is spin coated and CH3NH3I (MAI) is electro-sprayed on the PbI2 layer. The electro-sprayed perovskite film was then annealed at 100 °C for 5 min. A detailed investigation of the effect of various electrospray parameters such as, deposition time, MAI concentration, substrate-to-nozzle distance, and flow rate (droplet size), on the performance of the solar cells is carried out.

The key features of the electrospray-based deposition are: 1) precisely controlled reaction between the two precursors, by gradually supplying MAI nanoparticles onto the PbI2 layer and 2) intermediate phase formation during the electrospray of MAI nanoparticles. Both of these characteristics lead to the formation of ultra-smooth and moisture-resistant perovskite film. Smoothness of the film is examined by atomic force microscopy (root mean square roughness is 31 nm for electrosprayed perovskite film and 58.9 nm for spin coated film over a large area of 50 μm × 50 μm) and moisture-resistance is examined by contact angle measurement (66.09° for electrospray film and 33.01° for spin coated sample). The intermediate phase formation is characterized by X-ray diffraction (XRD) and change in the XRD pattern is observed during annealing. The cells fabricated using the electrospray are more efficient (up to 12%) and highly stable (up to 5.5 months) under ambient condition than the cells prepared using a conventional spin coating method. Additionally, the electrospray-deposited film exhibits self-healing behavior when exposed to moisture. Material stability is also investigated by monitoring the amount of PbI2 generating from the perovskite degradation and is correlated to the device stability. Electrospray also provides precise control over the material required to form the perovskite layer, reducing material loss. Therefore, electrospray technique is promising for the large-scale fabrication of stable and efficient perovskite solar cells under ambient condition. Details of the electrospray-assisted system and highly stably perovskite formation using this technique will be presented.

Reference:

Kavadiya, S. et al., Advanced Energy Materials, 10.1002/aenm.201700210