[18p-Z20-1~12] 12.5 Organic solar cells

▲ [18p-Z20-8] Combining surface passivation and Br anion addition to achieve efficiency more than 22% in tin-lead perovskite solar cells

〇(P)Gaurav Kapil¹, Takeru Bessho², Qing Shen¹, Hiroshi Segawa², Shuzi Hayase¹ (1.Uni. of Electr-Comm., 2.Uni. of Tokyo)

Keywords:Tin-lead perovskite, Surface passivation, Low voltage loss

Tin-lead (Sn-Pb) perovskite solar cells (PSCs) are now getting great attention due to the rapid increase in photoconversion efficiency (PCE) more than 20%, which brings them near to their Pb counterparts [1]. They possess the bandgap of 1.2-1.3 eV, which is according to Shockley-Queisser (SQ) limit can give higher PCE than Pb-PSCs where bandgap lies in between 1.45-1.55 eV. Also, according to SQ limit the Voc of 0.9-1 eV is possible for the solar absorbing materials with a bandgap of 1.2-1.3 eV [2]. In our previous work, we have reported a PCE of 20.4% using Cs_0.025FA_0.475MA_0.5Sn_0.5Pb_0.5I₃ (1.27 eV) perovskite as the absorber layer in PSCs with a Voc of 0.81 V [3]. In the work, we revealed that lattice strain relaxation is one of the important properties to look for cation mixing at A position of ABX₃ (where, A is monovalent cation, B is bivalent cation and X is halide anion) perovskite. Therefore, following the same strategy, in the present research, we added a small fraction of Br anion with I anion at X position that led to further decrease in lattice strain and reduction of urbach energy that resulted into increase in Voc. In addition to this, we used Lewis base surface passivation that solved the two major problems of Sn-Pb perovskite, first is the reduction in formation of amount of Sn⁴⁺ and second is neutralization of positive surface of perovskite due to I anion vacancy.
References
K. Xiao and H. Tan et al., Nature Energy, 2020, 5, 870-880.
W. Shockley, H. J. Queisser, J. Appl. Phys. 1961, 32, 510.
G. Kapil and S. Hayase et al., ACS Energy Letters, 2019, 4, 1991-1998.