Layered Mixed Tin–Lead Hybrid Perovskite Solar Cells with High Stability

Abstract

For neat Pb perovskites, two-dimensional (2D) hybrid perovskites, where n layers of inorganic material are separated by a long-chain organic cation, generally exhibit greater stability but have lower photovoltaic performance characteristics, motivating the study of 2D/3D mixeddimension systems to realize both high efficiency and stability. In this Letter, we demonstrate such optimal compromise between performance and stability using formamidinium, cesium, and t-butylammonium as A-site cations with Pb:Sn mixed-metal low-band-gap perovskites. Perovskite solar cells based on n = 4 and 5 lead−tin perovskites achieved power conversion efficiencies of up to 9.3 and 10.6%, respectively, and correspondingly retained 47 and 29% of their initial efficiency during storage in nitrogen for 2000 h. A similar stability trend for n = 4 over n = 5 was also observed for unencapsulated devices during continuous operation under a combined air atmosphere and temperature for 10 h, resulting in improved stability over the 3D lead−tin counterpart.

Extending Carrier Lifetimes in Lead Halide Perovskites with Alkali Metals by Passivating and Eliminating Halide Interstitial Defects

“…They have been the focus of intense recent attention owing to their remarkable photoelectric properties, including large charge carrier diffusion lengths, long charge carrier lifetimes, small exciton binding energies, and high absorption coefficients . Combined with simple synthetic procedures, these unique optoelectronic characteristics lead to diverse applications in photoelectric devices, such as sensors, light‐emitting diodes, photocatalytic water‐splitting assemblies, and solar cells . In particular, the power conversion efficiency of HOIP solar cells has rapidly increased from 3.8 % to 25.2 % in recent years, close to that of single‐crystalline silicon solar cells .…”

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.…”

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

“…Incorporation of layered perovskites to form 2D/3D hybrid structures is a promising approach to resolve this dilemma, as seen in lead‐based PSCs 17–21. Layered perovskites have the chemical formula of A 2 (FA/MA/Cs) n −1 (Pb/Sn) n (Br/I) 3 n +1 , where A is the bulky organic cation attached to the corner‐sharing [PbI 6 ] or [SnI 6 ] octahedral framework.…”

“…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…”