Electrode-induced impurities in tin halide perovskite solar cell material CsSnBr3 from first principles

Abstract All-inorganic lead-free CsSnBr₃ is attractive for applications in solar cells due to its nontoxicity and stability, but the device performance to date has been poor. Besides the intrinsic properties, impurities induced from electrodes may significantly influence the device performance. Here, we systematically studied the stability, transition energy levels, and diffusion of impurities from the most commonly used electrodes (Au, Ag, Cu, graphite, and graphene) in CsSnBr₃ based on density functional theory calculations. Our results reveal that, whereas graphite and graphene electrodes exhibit negligible influence on CsSnBr₃ due to the relatively high formation energies for carbon impurities in CsSnBr₃, atoms from the metal electrodes can effectively diffuse into CsSnBr₃ along interstice and form electrically active impurities in CsSnBr₃. In this case, a significant amount of donor interstitial impurities, such as $$Ag_i^ +$$, $$Cu_i^ +$$, and $$Au_i^ +$$, will be formed under p-type conditions, whereas the Sn-site substitutional acceptor impurities, namely $$Au_Sn^{2 -} $$, $$Ag_Sn^{2 -} $$, and $$Cu_Sn^{2 -} $$, are the dominant impurities, especially under n-type conditions. In particular, except for $$Au_i^ +$$, all these major impurities from the metal electrodes act as nonradiative recombination centers in CsSnBr₃ and significantly degrade the device performance. Our work highlights the distinct behaviors of the electrode impurities in CsSnBr₃ and their influence on the related devices and provides valuable information for identifying suitable electrodes for optoelectronic applications.