Enhanced TiO2/MAPbI3Electronic Coupling by Interface Modification with PbI2

Organohalide lead perovskites are revolutionizing the landscape of emerging photovoltaic technologies. From their first application in 2009 by Kojima et al.1a as solar cells sensitizers and the first report of solid state solar cells by Kim et al.,1b photovoltaic devices based on these materials showed a fast and continuous increase in their efficiency,2,3 with very recent certified efficiency exceeding 22%.4 These materials can be solution-processed at low-temperature5 and vapor-deposited,2 realistically holding the promise to reach comparable efficiency as conventional thin-film photovoltaic technologies. Furthermore, they can be combined with organic electron acceptors/donors, to deliver flexible photovoltaic devices.6−8 Methylammonium leadiodide, hereafter MAPbI3, and the related mixed halide MAPbI3−xClx analogue have dominated the field. These perovskites can support both electron and hole transport,5,9,10 giving rise to a variety of device architectures, being employed as solar cell sensitizers when deposited on n-transporting mesoporous TiO2, or serving both as light absorber and electron transporter in meso-superstructured and planar heterojunction solar cells.