Inkjet Printing All Inorganic Halide Perovskite Inks for Photovoltaic Applications

Dieter Weber synthesized the first organic-inorganic hybridhalideperovskites in 1978^1,2. Roughly 30 years later in 2009, Akihiro Kojima and collaborators fabricated photovoltaic devices using the same organic-inorganic hybridhalideperovskites synthesized by Weber, namely, CH₃NH₃PbI₃ and CH₃NH₃PbBr₃³. These experiments were the beginning of a subsequent tidal wave of research focusing on the photovoltaic properties of organic-inorganic hybrid halide perovskites. From 2009 to 2018, the device power conversion efficiency dramatically increased from 3.8%³ to over 23%⁴, making organic-inorganic hybridhalide perovskites comparable to Si-based solar cells. As with the organic-inorganic halide-based perovskites, the inorganic halide-based perovskites started gaining traction in the research community around 2012 when the first photovoltaic device efficiency was measured to be 0.9%⁵. Since 2012 the all inorganic halide-based perovskites have come a long way with some device efficiencies measured to be over 13% as in the 2017 study by Sanehira et al.⁶Both the organic-based and inorganic-based perovskites find applications related to lasers^7,8,9,10, light emitting diodes^11,12,13, high energy radiation detection¹⁴, photo detection^15,16, and of course photovoltaic applications^5,15,17,18. Over almost the past decade, many different synthesis techniques have emerged from scientists and engineers ranging from solution processed methods to vacuum vapor deposition techniques^19,20,21. The halideperovskites synthesized using a solution-processed method are advantageous as they can easily be employed as inks for inkjet printing¹⁵.

In 1987, the first reported use of inkjet printing of solar cells was presented. Since then, scientists and engineers have sought ways to successfully print all inorganic solar cells with attractive performance properties and low implementation costs²². There are many advantages to inkjet printing solar cells, as compared to some of the common vacuum based fabrication methods. An important aspect of the inkjet printing method is that solution-based materials are used as inks. This opens the door for trials of many different materials, such as inorganicperovskite-based inks, which can be synthesized by facile wet chemical methods. In other words, inkjet printing of solar cell materials is a low-cost route to rapid prototyping. Inkjet printing also has the advantages of being able to print large areas on flexible substrates and print by design at low temperatures in atmospheric conditions. Furthermore, inkjet printing is highly suitable for mass production allowing for realistic low cost roll-to-roll implementation^23,24.

In this article, we first discuss the steps involved with synthesizing inorganicperovskite quantum dot inks for inkjet printing. Then, we describe the additional steps for preparing inks for printing and the actual procedures for inkjet printing a photoactive film using a commercially available inkjet printer. Finally, we discuss the characterization of the printed films which is necessary to ensure the films are of proper chemical and crystal composition for high quality device performance.