We propose to perform high-resolution fluorescence-detected XANES (HERFD-XANES) at the Pb and Bi L3 edges to clarify how Bi3+ heterovalent doping changes the electronic structure and electron transport properties of a one-dimensional hybrid halide pseudo-perovskite, (TMSO)PbI3 (TMSO = (CH3)3SO+), either undoped, lightly or heavily doped. In this way, we will get helpful information about the doping-electron properties relationship and, ultimately, about the fundamental understanding of hybrid perovskites in thermoelectric or optoelectronic devices.