Role of the Dopants on the Morphological and Transport Properties of Spiro MeOTAD Hole Transport Layer
The use of a solid hole transport layer (HTL) was transformational for the recent perovskite solar cell (PSC) revolution in solar energy technology. Often high efficiency PSC devices employ heavily doped hole transport materials such as spiro MeOTAD. Independent of HTL chemistry, lithium bis trifluoromethanesulfonyl imide (LiTFSI) and tert butylpyridine (TBP) are commonly used as additives in HTL formulations for PSCs. LiTFSI and TBP were originally optimized for dye sensitized solar cells, where their roles have been extensively studied. However, in the case of PSCs, the function of TBP is not clearly understood. In this study, properties of the HTL composite deposited on flat silicon substrates were systematically measured at several length scales, e.g. macroscopically (profilometry, 4 point probe conductivity, and thermogravimetry differential thermal analysis) microscopically, and at the nanoscale to investigate film morphology, conductivity, and dopant distribution. Microscopic distributions of spi.