Suppressing Nonradiative Recombination in Lead–Tin Perovskite Solar Cells through Bulk and Surface Passivation to Reduce Open Circuit Voltage Losses

Abstract

Lead−Tin perovskite solar cells (Pb/Sn PSCs) are limited by the intrinsic instability of Sn(II), which tends to oxidize forming Sn vacancies in perovskite films. Herein, a Lewis base β-guanidinopropionic acid (GUA) and hydrazinium iodide (HAI) are introduced to effectively passivate the perovskite bulk and surface, respectively. The synergistic approach leads to Pb/Sn PSCs with a promising power conversion efficiency of 20.5% owing to the significantly reduced nonradiative recombination and voltage losses. As a result, the V OC × FF product of PSCs is significantly improved, which is among the highest values documented in the literature, being favorable for perovskite-based tandem applications. Additionally, the strategy demonstrated in this work could also improve the stability of PSCs by enhancing the chemical robustness of the perovskite layer. These results emphasize the significance of bulk and surface passivation in the development of efficient and stable PSCs based on Pb/Sn perovskites.

Additive Engineering for Mixed Lead–Tin Narrow-Band-Gap Perovskite Solar Cells: Recent Advances and Perspectives

“…94 Therefore, effective defect suppression can be achieved by the surface passivation strategy through appropriate treating methods. 143 As mentioned before, the use of a 2D surface passivation layer can efficiently reduce the defect concentrations at GBs and on the film surface, which prohibited the corrosion of oxygen and water into the perovskite lattice to improve the cell performance. For instance, Hu et al have added a SnF 2 •3FACl additive into the all-inorganic CsPb 0.6 Sn 0.4 I 3 precursor solution to prohibit the Sn 2+ oxidation and functionalize GBs.…”

“…Therefore, several functional additives for the Sn 2+ cation stabilization, such as Sn metal powder, SnF 2 , and organic reducing agents, to the perovskite precursor solution effectively inhibited the Sn 2+ cation oxidation, reducing the defect density of Pb–Sn NBG PSCs. , For the Pb–Sn perovskites, it has been reported that the Sn 2+ oxidation mainly occurs at the GBs and on the surface of the perovskite film . Therefore, effective defect suppression can be achieved by the surface passivation strategy through appropriate treating methods . As mentioned before, the use of a 2D surface passivation layer can efficiently reduce the defect concentrations at GBs and on the film surface, which prohibited the corrosion of oxygen and water into the perovskite lattice to improve the cell performance.…”

“…147 Zhang et al have introduced a Lewis base β-guanidinopropionic acid (GUA) as an additive into MA 0.3 FA 0.7 Pb 0.5 Sn 0.5 I 3 precursor solution and hydrazinium iodide (HAI) into isopropanol (IPA) antisolvent to passivate the perovskite film surface before and after the thermal annealing, respectively. 143 It was found that the guanidine and carboxyl functional groups in the GUA additive effectively regulated the crystallization behavior of Pb−Sn perovskites by coordinating with Pb 2+ /Sn 2+ cations and reducing the amount of deep-level antisite defects. The reducing hydrazine group in the HAI additive introduced into IPA antisolvent remarkably inhibited the Sn 2+ oxidation, effectively passivating surface defects of the perovskite film.…”

“…In addition, CF3-PA-additive-engineered all-perovskite TSCs maintained 90% of primary PCE after 600 h of MPPT operation under 1 sun irradiation in ambient air, which was much more superior to that of the pristine cell (Figure e) . Zhang et al have introduced a Lewis base β-guanidinopropionic acid (GUA) as an additive into MA 0.3 FA 0.7 Pb 0.5 Sn 0.5 I 3 precursor solution and hydrazinium iodide (HAI) into isopropanol (IPA) antisolvent to passivate the perovskite film surface before and after the thermal annealing, respectively . It was found that the guanidine and carboxyl functional groups in the GUA additive effectively regulated the crystallization behavior of Pb–Sn perovskites by coordinating with Pb 2+ /Sn 2+ cations and reducing the amount of deep-level antisite defects.…”

DMSO‐Free Solvent Strategy for Stable and Efficient Methylammonium‐Free Sn–Pb Alloyed Perovskite Solar Cells

“…For another example, the Sn(IV) generated during aging process can migrate from the film and leave in situ ionic vacancy sites, leading to the unsaturated coordination in crystal lattice and accelerating the film decomposition rates. [11,12] More recently, Sargent et al observed that the Sn(IV) can be initially created during the dissolution of precursors and the annealing of the film, since the conventional solvent DMSO can oxidize Sn(II) at temperatures above 100 °C. [13] Therefore, more attention should be paid to find new friendly solvents to replace DMSO and suppress the oxidation process of Sn(II) at precursor annealing or film annealing stages.…”