This special series of the Journal of Photonics for Energy focuses on the science and technology of the so-called perovskite-based solar cells. These materials have been named for their perovskite crystal structure that adopts an ABX₃ composition, where for example A = formamadinium-FA, methylammonium-MA, Cs, and/or Rb; $\mathrm{B}={\mathrm{Pb}}^{2+}$, and/or ${\mathrm{Sn}}^{2+}$; and $X={\mathrm{Cl}}^{-}$, ${\mathrm{Br}}^{-}$, and/or ${\mathrm{I}}^{-}$. These materials have gained a lot of attention due to rapid rise in performance, reaching current record certified efficiencies of 22.1%.¹ In spite of their quickly achieved high efficiencies, there is still much to learn about the synthesis and properties of these materials. Here we display a series of new findings and perspectives on a variety of related topics.

The collection of papers were published in the Journal of Photonics for Energy, throughout Volumes 6 and 7:

Goudarzi et al. present a simulation of two different processing methods for the inverted perovskite solar cell geometry and report a drastically different interface defect density between the two preparations. Habibi et al. describe a spray coating method for sequentially depositing planer perovskite-based solar cells, addressing a critical need for scalable processing methods for these materials. Szostak et al. present a comprehensive study into the intramolecular exchange method for synthesizing perovskite-based ${\mathrm{MAPbI}}_3$ solar absorbers and propose a mechanism for the direct formation of the ${\mathrm{MAPbI}}_3$ film. Peng et al. explore the potential to replace ${\mathrm{TiO}}_2$ with CdS as a higher performing electron transport layer of a perovskite-based solar cell, achieving a photoconversion efficiency of 16.1%.

Ananthakumar et al. provide a review of the synthesis, properties, and applications for cesium lead halide perovskite quantum dots (QDs). These QDs have higher quantum yield (90%) than any other semiconductor QDs making them a promising candidate for a variety of device applications. Since this report researchers have reported ${\mathrm{CsPbI}}_3$ QD devices with a certified device efficiency of 13.43%,² a current QD device record. Hariz and Song et al. present two perspective views on perovskite-based solar cells and provide commentary on potential pathways to higher performance.

The articles in this special series provide a snapshot of the rapidly advancing field of perovskite-based solar cells. We hope these works provide inspiration for new areas of research while also providing a perspective outlook on this exciting field.