Stable Sn/Pb-Based Perovskite Solar Cells with a Coherent 2D/3D Interface

Abstract

SummaryLow-band-gap metal halide perovskite semiconductor based on mixed Sn/Pb is a key component to realize high-efficiency tandem perovskite solar cells. However, the mixed perovskites are unstable in air due to the oxidation of Sn2+. To overcome the stability problem, we introduced N-(3-aminopropyl)-2-pyrrolidinone into the CH3NH3Sn0.5Pb0.5IxCl3-x thin film. The carbonyl group on the molecule interacts with Sn2+/Pb2+ by Lewis acid coordination, forming vertically oriented 2D layered perovskite. The 2D phase is seamlessly connected to the bulk perovskite crystal, with a lattice coherently extending across the two phases. Based on this 2D/3D hybrid structure, we assembled low-band-gap Sn-based perovskite solar cells with power conversion efficiency greater than 12%. The best device was among the most stable Sn-based organic-inorganic hybrid perovskite solar cells to date, keeping 90% of its initial performance at ambient condition without encapsulation, and more than 70% under continuous illumination in an N2-filled glovebox for over 1 month.

Combining Efficiency and Stability in Mixed Tin–Lead Perovskite Solar Cells by Capping Grains with an Ultrathin 2D Layer

“…As seen in Table S1 (Supporting Information), the PCE improvement by the PEA cation passivation comes from an increased open‐circuit voltage which we associate with defect passivation; and increased FF that we assign further to the minimal formation of carrier‐retarding layered perovskite 27,37–39. The FF (76%) obtained here is higher than that for the layered perovskite‐based Sn–Pb PSCs (below 70%) 19,22…”

“…Until now, the conventional 2D/3D strategy has not translated into both stable and efficient Sn–Pb PSCs 19,22–24. It can increase stability in Sn–Pb devices, but such an excess of bulky organic cation was required that a low fill‐factor (FF < 70%) was obtained—presumably arising from blocked out‐of‐plane carrier transport in layered perovskites 25,26…”

Controlling the Growth Kinetics and Optoelectronic Properties of 2D/3D Lead–Tin Perovskite Heterojunctions

“…Our photophysical measurements here demonstrate the signature of this energy cascade process in these heterostructures, which could be used for LEDs operating more stably and with emission deeper in the NIR than the typical lead‐only systems . The uncontrolled degree of formation of 2D and 3D domains has limited the use of both of these applications for Pb:Sn systems to date . Such device applications will require tailored optimization of the heterostructures and will be the subject of future work.…”

“…The hydrophobicity of the large cations could be particularly beneficial for the Sn and mixed‐Pb:Sn systems as the 2D component could inhibit oxygen‐ and water‐induced degradation pathways, bringing substantial improvements in ambient stability. Indeed, recent works demonstrated substantial improvements in mixed‐Pb:Sn device operation and stability by employing 2D structures utilizing spacer molecules such as phenethylammonium (PEA) and other analogues . However, these device‐focused studies do not allow one to ascertain information about the formation of the 2D component, how the fraction of 2D can be controlled and how the 2D component can influence carrier recombination and material stability.…”

Triple-cation low-bandgap perovskite thin-films for high-efficiency four-terminal all-perovskite tandem solar cells

“…Therefore the Sn-Pb-based PSCs suffer from lower stability even in an inert atmosphere with a trace amount of oxygen. 18,25,26 The most common strategies to prevent oxidation are incorporating antioxidant additives such as SnF 2 , [26][27][28][29][30] SnBr 2 , 26,27,31 SnCl 2 , 27,32 GuaSCN, 17 ascorbic acid, 33 and sulfonic acid group, 34 applying 2D components as passivation layers, [35][36][37] compositional engineering, 38 as well as utilizing Sn-reduced precursor solutions. 18,39 In addition to the oxygen-induced degradation, other possible degradation mechanisms such as thermal decomposition, 40,41 light-induced degradation, 41,42 and crystal-structure transition 43,44 are less explored for Sn-Pb-based PSCs.…”