Passivation of 3D perovskites with fluorine compound for highly efficient perovskite solar cells

Perovskite solar cells (PSC) achieved a certified power conversion efficiency (PCE) that was 27 % for single junction cell, which demonstrated a great possibility of being next generation solar cells. However, different heterojunction interfaces generate the defect sites, which cause the nonradiative recombination, resulting in the decreases the device stability as well as an efficient charge extraction. One of the most effective strategies to reduce the defect sites is the surface passivation which suppress the nonradiative recombination at the interface and bulk of the perovskite layer. Herein, it was demonstrated that the ammonium trifluromethansulfonate (AFS), trifluoroacetamidine (TFA), and tetrahydrofurfuryamine (TFF) were applied into the (Cs_0.05MA_0.05FA_0.9Pb(I_0.95Br_0.05)₃) perovskite film in order to passivate the defect sites. AFS molecule that contains both Lewis acid and base exhibited effective binding to the defect sites as well as the grain boundaries among the tree molecules. It increases the grain size and intrinsic stability to the ambient stimuli. Thus, the AFS modified PSC demonstrated the highest PCE of 17.69 %. The anion and cation nature of AFS facilitates the decrease of the radiative recombination, which boosts the carrier lifetime. AFS modified PSC more importantly retains more than 80 % of its initial PCE after 2000 h of being tested without encapsulation at 30 % relative humidity and 25 °C. This study provides a design for the passivator molecule in order to effectively passivate the recombination sites in perovskite film, which resulted in an enlarged grain size and an increase of the intrinsic stability to the humidity condition.