Self-Assembled Monolayer (SAM) Forming Hole Transport Materials

　Perovskite solar cells have developed significantly over the last 10 years, since the first report was published by Miyasaka et al.¹⁾ The power conversion efficiency has been demonstrated to be 25.2% for a small cell, 16.09% for a module, and 29.15% for a perovskite/silicon tandem.²⁾ One of the main bottlenecks to large-scale production is the hole transport layer. Many researchers have undertaken the challenged of stabilizing and upscaling perovskite solar cells for practical use. Conventional hole-transport materials such as Spiro-OMeTAD and PTAA are expensive and are destabilized by the addition of dopants to provide carrier transport.
　Recently, Getautis and Albrecht et al. have developed the hole-selective self-assembled monolayer (SAM) forming agents, 2PACz (1) and MeO-2PACz (2), for high-performance perovskite solar cells. 1 and 2 can form a monolayer on a metal oxide surface anchored by a phosphonic acid moiety. These materials are useful for tandem solar cell because they make allow conformal coverage of rough surfaces. A perovskite solar cell using a SAM hole transport layer can realize more than 20% efficiency without any dopants, and is very cost effective due to the extremely low material consumption.³⁾