A research team led by Researcher Liang Jia of Fudan University published a research paper titled "Iodide Management and Oriented Crystallization Modulation for High-Performance All-Air Processed Perovskite Solar Cells" in Nature Communications. Team member Li Tianpeng is the first author of the paper, and Researcher Liang Jia is the corresponding author.
Key Highlights: This paper proposes a novel electron transport layer based on a metal chalcogenide (Sn(S0.92Se0.08)2) to address the low VOC issue caused by energy level mismatch in non-lead perovskite (tin-based perovskite) solar cells. The resulting non-lead perovskite solar cell achieves a PCE of up to 11.78% and a high VOC of 0.73 V. The device also maintains a high stability, retaining over 95% of its initial efficiency after 1632 hours.
Tin-based perovskite solar cells have attracted attention due to their biocompatibility, narrow bandgap, and long hot carrier lifetime. However, n-i-p-type tin-based perovskite solar cells (TPSCs) have performed poorly, largely due to the indiscriminate use of metal oxide electron transport layers (METLs) originally designed for n-i-p-type lead-based perovskite solar cells. This poor performance is primarily due to two factors: the desorption of oxygen molecules from oxygen vacancies, which leads to the oxidation of Sn2+ to Sn4+ in the tin-based perovskite, and the energy level mismatch of TiO2 ETLs, which results in a reduced VOC. To address these issues, the team led by Researcher Liang Jia from Fudan University introduced an ETL, a metal mixed chalcogenide of Sn(S0.92Se0.08)2, into n-i-p-type TPSCs. Both experimental and theoretical structures demonstrate that the Sn(S0.92Se0.08)2 ETL not only prevents the desorption of O2 molecules but also hinders the reaction between Sn2+ in the tin-based perovskite and O2 present in air, providing a shallower CBM position, improved morphology, enhanced conductivity, and increased electron mobility. These properties significantly improve the VOC of the n-i-p TPSC with a Sn(S0.92Se0.08)2 ETL, from 0.48 V to 0.73 V, and boost the PCE from 6.98% to 11.78%, an improvement of over 65%. Furthermore, this ETL significantly enhances the operational stability of the n-i-p TPSC.
Finally, the researchers examined the long-term stability of n-i-p TPSCs with TiO2, SnS2, and Sn(S0.92Se0.08)2 ETLs under ambient conditions. The PCE of the n-i-p TPSCs encapsulated with TiO2, SnS2, and Sn(S0.92Se0.08)2 ETLs varied with aging. Clearly, the degradation levels of the three devices differed significantly. The PCE of n-i-p TPSCs using TiO2 ETL dropped rapidly after 912 h, and only retained 40% of the initial efficiency after 1080 h; the n-i-p TPSCs using SnS2 ETL still retained more than 80% of the initial efficiency after 1632 h; and the n-i-p TPSC using Sn(S0.92 Se0.08 )2 ETL still retained more than 95% of its initial efficiency after 1632 h, which is of great significance for practical applications.
Fig. 1 | Oxygen vacancies in TiO2 ETLs. a) Schematic diagram of the buried interface between the TiO2 ETL and Sn-based perovskite layer. Oxygen desorption from OVs in the TiO2 ETL accelerates the oxidation of Sn2+ to Sn4+ within the Sn-based perovskite. b) EPR spectra of the TiO2 ETL, confirming the existence of OVs. c ) Highresolution XPS spectra in the O 1 s region of the TiO2 ETL, further supporting the existence of OVs. High-resolution XPS spectra of Sn-based perovskite films on (d) FTO and (e) FTO/TiO2 substrates after aging for 14 days, respectively. This distinct difference observed suggests that desorbed oxygen from TiO2 films leads to severe oxidation in Sn-based perovskites.
Fig. 2 | Metal chalcogenide ETLs. UPS spectra of VBM onset and photoemission cutoff energy boundary of (a) SnS2 and (b) Sn(S0.92Se0.08)2 ETLs. The Sn(S0.92Se0.08)2 ETL shows the shallowest CBM position, highlighting its potential as the preferred ETL candidate for nip-type TPSCs. c ) KPFM curves and images of the TiO2, SnS2 and Sn(S0.92Se0.08)2 ETLs. The scalebars are 1 μm. d) UV-vis optical transmission spectra of TiO2, SnS2 and Sn(S0.92Se0.08)2 ETLs, revealing similar optical transparency between the Sn(S0.92Se0.08)2 ETL and the TiO2 ETL throughout the spectrum. e) J-V curves at the trap-free SCLC regime of TiO2, SnS2 and Sn(S0.92Se0.08)2 ETLs, fitted with the Mott-Gurney law. The results suggest that the mobility of the Sn(S0.92Se0.08)2 ETL is an order of magnitude higher than that of the TiO2 ETL.
Fig. 3 | Strong interaction between metal chalcogenide ETLs and Sn-based perovskite layers. The electron density distribution of Sn-based perovskites interacting with (a) O2, (b) SnS2 and (c) Sn(S0.92Se0.08)2 molecules, indicating that the Sn(S0.92Se0.08)2 ETL not only circumvents O2 molecules desorption, but also inhibits the reaction between Sn2+ ions in Sn-based perovskites and O2 molecules present in air. GIWAXS patterns of the Sn-based perovskite films grown on (d) TiO2, (e) SnS2, and (f) Sn(S0.92Se0.08)2 ETLs respectively. These results indicate that the Sn(S0.92Se0.08)2 ETL induces the highest crystalline phase purity at the buried interface due to the strong interaction. g) The Sn4+/Sn2+ ratios in the Sn 3d5/2 and Sn 3d3/2 regions of the Sn-based perovskite films deposited on different ETLs, including TiO2, SnS2 and Sn(S0.92Se0.08)2 ETLs. The Sn-based perovskite with the Sn(S0.92Se0.08)2 ETL shows the lowest values, indicative of the strongest interaction between the two. h) PL and (i) TRPL spectra of Sn-based perovskite films deposited on TiO2, SnS2, and Sn(S0.92Se0.08)2 ETLs, respectively. Both results suggest the fastest electron transfer in the structure of Sn-based perovskite films deposited on Sn(S0.92Se0.08)2 films.
Fig. 4 | Photovoltaic performance of TPSCs with metal chalcogenide ETLs. a) Schematic diagram of nip-type TPSCs with the structure of FTO/ETL/Sn-based perovskite/PTAA/Ag, utilizing TiO2, SnS2, and Sn(S0.92Se0.08)2 films as ETLs. b )J–V curves of nip-type TPSCs with TiO2, SnS2 and Sn(S0.92Se0.08)2 ETLs, respectively. c) A comparison of PCE between this work and other reported PCEs (over 6.5%) of niptype TPSCs. The impressive PCE of the nip-type TPSC with the Sn(S0.92Se0.08)2 film significantly surpasses those of previously reported nip-type TPSCs with TiO2 films.d) EQE spectra and integrated Jsc values of the nip-type TPSCs with TiO2, SnS2 and Sn(S0.92Se0.08)2 ETLs, respectively. e) Nyquist plots. f dark J–V curves, and (g) stabilized power output of nip-type TPSCs with TiO2, SnS2 and Sn(S0.92Se0.08)2 ETLs respectively. These result indicate that the nip-type TPSC with the Sn(S0.92Se0.08)2 ETL showcases the reduced charge transfer resistance, fastest electron transport, and lowest defect density among the three types ETLs. h) Normalized PCE of unencapsulated nip-type TPSCs with TiO2, SnS2 and Sn(S0.92Se0.08)2 ETLs for over 1600 h in an N2 glovebox. These findings collectively support the potential of metal chalcogenide ETLs, particularly Sn(S0.92Se0.08)2, for advancing the performance and stability of nip-type TPSCs.
本文来源：DOI: 10.1038/s41467-024-53713-4
https://doi.org/10.1038/s41467-024-53713-4