Tin-Based Defects and Passivation Strategies in Tin-Related Perovskite Solar Cells

Abstract

Tin (Sn)-based and mixed tin−lead (Sn−Pb) perovskites have attracted increased attention as promising candidates for new generation lead-free perovskite and all-perovskite tandem solar cells. However, as an inevitably critical issue, Sn(II) induced serious defects and oxidation and caused poor photovoltaic performance and unsatisfactory stability for Sn-based and mixed Sn−Pb perovskites. Herein, a comprehensive understanding on defect classification, defect formation, defect effect on performance, and defect passivation strategies is reviewed on the Sn(II) induced defects. The Sn(II)-based defects can be classified from the aspects of defect dimensions and shallow/deep levels in energy structure according to three main origins, i.e. low defect tolerance, oxidation, and fast crystallization. Then, the state-of-the-art defect passivation strategies including surface Lewis acid/base coordination, low/mixed dimensional perovskite design, composition regulation and crystal orientation modulation, and reducing agent assistance are summarized systematically. Lastly, several key scientific issues and future research prospectives are proposed for achieving stable and high-performance Sn-related perovskite photovoltaics.

Optoelectronic Properties of Tin–Lead Halide Perovskites

“…A full discussion of these is beyond the scope of this review, and we refer the reader to several existing reviews for full details. 25 , 48 − 50 Currently, the most frequently utilized approach involves the addition of SnF 2 to the precursor solution, which reduces the formation prospects of tin-poor stoichiometries. 28 , 29 , 42 As Figure 1 illustrates, SnF 2 addition to tin–lead halide perovskites considerably lowers the density of background holes (p-type doping), 28 , 29 , 42 in particular for tin-rich stoichiometries.…”

Crystallization Dynamics of Sn‐Based Perovskite Thin Films: Toward Efficient and Stable Photovoltaic Devices

“…So far, there are many comprehensive reviews in this field focusing on the current development and future perspective of Sn-based perovskite in terms of preparation, stability, and efficiency of their PSCs. [23,25,31,32] However, although some parts of the reported reviews involve the brief discussion on the crystallization of Sn-based perovskite film, none of them pay particular attention and give a full-view on the crystallization dynamics of Sn-based perovskite film, which is expected to provide more practical guideline for further improvement of Sn-based PSCs. Therefore, it is of urgency at this stage to give a timely topic review to summary the current development of crystallization dynamics regulation on Sn-based perovskite film and their impact on the photovoltaic performance of PSCs.…”

“…[12,20] It should be noted that the uncontrollable crystallization process of Sn-based perovskites does not directly lead to poor solar cell performance, but the formed defects, film morphology, crystallinity and orientation, structural distribution, and residual strains induced during crystallization do, which are the direct factors affecting the performance of PSCs. [21][22][23][24][25] For Sn-based perovskite, the uncontrollable crystallization process mainly originates from the unique property of Sn 2+ , including high Lewis acidity and easy oxidation of Sn 2+ . [26,27] On the one hand, due to the higher energy of 5p orbital compared to 6p orbital, the Lewis acidity of Sn 2+ is higher than that of Pb 2+ , resulting in the fast reaction rate of SnI 2 with MAI or FAI.…”

A Perspective on the Commercial Viability of Perovskite Solar Cells

“…[ 79,80 ] Substitution of lead (Pb) by tin (Sn) in the B‐site of the perovskite lattice further narrowed the energy gap from 1.31 to 1.1 eV (Figure 2d), with a PCE of ≈12% for Pb:Sn = 1:1. [ 81–85 ] Even though pure tin‐based halide has a narrower energy gap compared with its lead‐based counterpart, with the highest PCE recorded at 12.4%, the stability needs to be further improved for commercialization. [ 86–88 ]…”

“…[79,80] Substitution of lead (Pb) by tin (Sn) in the B-site of the perovskite lattice further narrowed the energy gap from 1.31 to 1.1 eV (Figure 2d), with a PCE of %12% for Pb:Sn ¼ 1:1. [81][82][83][84][85] Even though pure tin-based halide has a narrower energy gap compared with its lead-based counterpart, with the highest PCE recorded at 12.4%, the stability needs to be further improved for commercialization. [86][87][88] Other than flexibility in energy gap tuning, ambipolar transport properties of halide perovskite materials have also attracted considerable attention for applications other than PVs.…”