Quantitative Characterization of Ultrasonic Spray Coating of PbI2 for Perovskite Solar Cell Fabrication
Yabing Qi a, Shijin Zhang a, Sonia Ruiz Raga a, Mikas Remeika a
a Okinawa Institute of Science and Technology, 1919-1 Tancha Onna-son, Okinawa, 904-0495, Japan
Asia-Pacific International Conference on Perovskite, Organic Photovoltaics and Optoelectronics
Proceedings of International Conference Asia-Pacific Hybrid and Organic Photovoltaics (AP-HOPV17)
Yokohama-shi, Japan, 2017 February 2nd - 4th
Organizers: Tsutomu Miyasaka and Iván Mora-Seró
Poster, Mikas Remeika, 051
Publication date: 7th November 2016

Ultrasonic spray coating is a promising pathway to scaling-up of perovskite solar cell production because it can be applied on scales from < 1 cm2 laboratory samples to continuous roll-to-roll production.  The capability to optimize a scalable process in under laboratory conditions is particularly important because of dramatically lower cost of process development with table-top machines rather than large-scale industrial equipment.  Several groups have demonstrated fabrication of perovskite solar cells by ultrasonic spray coating, however the publications so far included only machine-specific parameters required to achieve optimal performance. Due to its inherent scalability, design of ultrasonic spray systems varies considerably, and settings on one machine are not necessarily meaningful on another. Even environmental factors and coated substrate area may considerably affect processing conditions and film quality for the same type of spray coating machine.

To identify machine-independent parameters that determine film quality, we demonstrate that spray-coated wet-film thickness and evaporation rate strongly correlate with dry film morphology and large-scale uniformity. To realize machine-independent process characterization, we demonstrate a system for in-situ measurement of wet film thickness and evaporation rate immediately after spray coating. We further demonstrate that with limited data, modeling can be used to compute wet film evaporation rate under conditions where in-situ measurement is not practical.  Monitoring wet film evaporation rate and thickness parameters directly would allow a process to be replicated between laboratories or manufacturing sites without the need for extensive re-optimization.  Furthermore, we demonstrate that the PbI2 films that were fabricated by the optimized process are suitable for high-performance perovskite solar cell fabrication under ambient conditions. Solar cells and modules are demonstrated with device active area between 1 cm2 and 2 cm2 and PCE up to 13% with negligible hysteresis. 

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