A typical perovskite solar cell consists of a hole transporting layer (HTL), a perovskite light absorber and an electron transporting layer (ETL). The most commonly studied HTL’s are organic/polymeric materials such as Spiro-OMeTAD(2,2',7,7'-tetrakis-(N,N-di-4-methoxyphenylamino)-9,9'-spirobifluorene ) or PTAA(poly(triaryl amine)), which are expensive and unstable in the presence of water vapor.
This presentation describes the application to perovskite solar cells of a new kind of inorganic HTL synthesized using atomic layer deposition (ALD). By alloying TiO2 with IrOx in a super-cycle ALD process, we found that the electron transporting material TiO2 becomes an effective HTL. Atomic layer deposition offers the prospect of depositing such hole contact materials over a wide variety of substrate materials and geometries, and with excellent control of layer thickness and composition. Previous research  on ALD-grown alloys of TiO2 and RuO2 showed that a large work function (~ 5.2 eV) can be achieved as result of a ~ 10 mol% RuO2 addition. In the current work, a Cs0.17FA0.83Pb(Br0.17I0.83)3 PSC including a TiO2-IrOx HTL of composition 20mol% IrOx and ~ 10 nm thickness achieved a high power conversion efficiency of 13.4% with 1.004 V open circuit voltage, which is 100 mV higher than the Voc of the reference device using a PEDOT:PSS. These results indicate that ALD-grown TiO2-transition metal oxide alloys are promising HTL’s for perovskite photovoltaics.
 O.L. Hendricks, A.G. Scheuermann, M. Schmidt, P.K. Hurley, P.C. McIntyre, and C.E.D. Chidsey, “Isolating the Photovoltaic Junction: Atomic Layer Deposited TiO2–RuO2 Alloy Schottky Contacts for Silicon Photoanodes,” ACS Appl. Mater. Interfaces 8, 23763-73 (2016).