The emergence of perovskite solar cells has been surprisingly rapid, and provide greater than 20% energy conversion efficiency, although they are produced by a simple spin coating technique. Recently, perovskite solar cell research has become increasingly popular in the field of solar cells.

Perovskite solar cells were first developed in 2005 at the Miyasaka laboratory in the Toin University of Yokohama. Although methylammonium lead halide perovskite materials are well known as highly luminescent materials, the combination between them and titanium oxide to produce solar cells had not been realized until 2005. Perovskite solar cells have been used in plastic-film-type dye-sensitized solar cells, which are prepared by a low-temperature printing process under ambient conditions. In this tutorial presentation, I would like to introduce a brief history of perovskite solar cells and several issues that we had to overcome in the first stages of the development of perovskite solar cells.

Recently, low-temperature processed plastic perovskite solar cells have been developed in our research group. In this tutorial course, I will also introduce some recent topics in perovskite research; for example, flexible solar cells, lead-free perovskite solar cells, and other relevant research topics.

Hybrid organic-inorganic perovskites are potential candidates to replace traditional silicon panels. They have captured the interest of solar researchers and energy policy experts because of their rapidly improving performance and low cost. On the market, the efficiency of the silicon panels ranges from about 17 to 20 percent . In the laboratory, perovskite cells have already surpassed 22 percent, and many researchers are confident that 25 percent could be reached soon . They are superior to silicon at absorbing light and can be fabricated using printing and roll-to-roll compatible techniques. This is in contrast with the costly and energy-intensive fabrication of traditional crystalline silicon-based photovoltaics. Perovskite solar cells have a great commercial potential, but there still remain a few challenges, which need to be resolved to prove the viability of the technology. Some of the well-known issues include material stability and presence of lead in the active layer. Furthermore, cost-effective, reliable fabrication process capable of delivering highly efficient, large-area perovskite modules is yet to be demonstrated. In my lecture, I would like to address practical aspects of bringing perovskite solar cells from a lab to the market. We will discuss viability and maturity of the technology from business perspective.

Theoretical conversion efficiency of a single-junction solar cell which band-gap is Eg1 is determined by transparency loss of low energy photons (hν<Eg1), thermal loss (hν-Eg1) of high energy photons (hν>Eg1) and diode losses (FF<100%, Voc<Eg1). Fundamental of higher efficiency multi-junction solar cells is to reduce the transparency loss and the thermal loss. Theoretical limit of conversion efficiency of single-junction and multi-junction solar cells is explained. Technologies for improving efficiency of Silicon and III-V compound solar cells are described. History of improving Silicon cell structure is to reduce the area of high carrier concentration region and metal contact region. Recent approach for Si is selective-contact which is to reduce recombination loss at the contact region. Compared with Si, there is big space to reduce the recombination loss in III-V cells. Recent technique for high efficiency III-V cells is photon-recycling which is to utilize luminescence due to radiative recombination. Fundamental technologies for high efficiency multi-junction solar cells such as current-matching are also described.

High efficiency, multi-junction (MJ) III-V solar cells are the preferred technology to provide power to the majority of spacecraft launched today. They are also a key component in terrestrial high-concentration PV applications, regularly achieving efficiencies greater that 40% under 500-1500x concentrated sunlight. In this tutorial, we will discuss key considerations in establishing and operating a foundry to produce MJ III-V solar cells.

Metal Organic Vapor Phase Epitaxy (MOVPE) is the preferred method for growing the active device layers in III-V MJ solar cells. We will discuss the design of an MOVPE facility including reactor types and selection, effluent handling and abatement, critical concerns for safety infrastructure, and high-level approaches to process control and quality assurance.

Having completed MOVPE growth, epitaxial wafers proceed through a series of wafer processing operations to convert them into finished solar cells. These steps include the deposition of anti-reflective coating layers to steer light into the device and contacting and metallization layers to efficiently extract the power generated in the solar cell. Unique aspects of III-V solar cell wafer processing, including the handling of thin germanium substrates and the challenges of accurately testing III-V MJ solar cells will also be discussed.