Ultralow Self-Doping in Two-dimensional Hybrid Perovskite Single Crystals

Unintentional self-doping in semiconductors through shallow defects is detrimental to optoelectronic device performance. It adversely affects junction properties and it introduces electronic noise. This is especially acute for solution-processed semiconductors, including hybrid perovskites, which are usually high in defects due to rapid crystallization. Here, we uncover extremely low self-doping concentrations in single crystals of the two-dimensional perovskites (C₆H₅C₂H₄NH₃)₂PbI₄·(CH₃NH₃PbI₃)_n-1 (n = 1, 2, and 3), over three orders of magnitude lower than those of typical three-dimensional hybrid perovskites, by analyzing their conductivity behavior. We propose that crystallization of hybrid perovskites containing large organic cations suppresses defect formation and thus favors a low self-doping level. To exemplify the benefits of this effect, we demonstrate extraordinarily high light-detectivity (10¹³ Jones) in (C₆H₅C₂H₄NH₃)PbI ₄·(CH₃NH₃PbI₃)_n-1 photoconductors due to the reduced electronic noise, which makes them particularly attractive for the detection of weak light signals. Furthermore, the low self-doping concentration reduces the equilibrium charge carrier concentration in (C₆H₅C₂H₄NH₃)₂PbI₄·(CH₃NH₃PbI₃)_n-1, advantageous in the design of p-i-n heterojunction solar cells by optimizing band alignment and promoting carrier depletion in the intrinsic perovskite layer, thereby enhancing charge extraction.