Efficient, inexpensive, lightweight and flexible solar cells are desired to help meet the world’s growing energy needs. Organometal halide perovskite (OMHP) photovoltaic (PV) cells have shown dramatic increases in solar cell efficiencies increase over the last 5 years. OMHP PV cells have attracted significant attention due to their broad absorption spectra, high electron and hole mobility, and low production cost. The interface between hole transporting layer (HTL) and perovskite thin films have a significant influence on charge transfer and overall solar cell performance. 2,2’,7,7’-tetrakis(N,N-di-p-methoxyphenylamine)9,9’-spirobifluorene (Spiro-OMeTAD) is a small molecule largely used as HTL in perovskite solar cells. However, this material suffers from low charge-carrier mobilities and inappropriate energy level alignments with some perovskites. In this work we investigate the effect of the HTL energetics on the performance of perovskite solar cells. This is accomplished through employing a range of HTLs with varying ionization energies (IEs). We find that the solar cell device performance is relatively insensitive to the IE of the HTL within a 0.4 eV range. We also demonstrate that modification of the HTL surface with different alcohols helps in increasing the solar cell performances
