Lattice stabilization and strain homogenization in Sn-Pb bottom subcells enable stable all-perovskite tandems solar cells

Abstract

All-perovskite tandem solar cells (PTSCs) offer a promising approach to surpass the Shockley-Queisser (SQ) limit, driven by efficiently reducing thermalization and transmission losses. However, the efficiency and stability of the narrow-bandgap (NBG) subcells, which are essential for PTSC performance, remain severely constrained by challenges such as lattice instability, strain accumulation and halide migration under illumination. This study introduces a rigid sulfonate-based molecule, sodium naphthalene-1,3,6-trisulfonate (NTS), into tin-lead (Sn-Pb) perovskites, where it strengthens the Sn-I bond through Sn-trisulfonate coordination and reduces light-induced dynamic lattice distortions via the rigid NTS backbone. These molecular interactions alleviate strain heterogeneity within the lattice and homogenize the Sn-Pb compositional gradient, thereby enhancing the structural integrity and long-term stability of Sn-Pb perovskites under operational conditions. As a result, Sn-Pb single-junction perovskite solar cells (PSCs) achieve a power conversion efficiency (PCE) of 23.2%. When integrated into a tandem configuration, the device attains an impressive PCE of 29.6% (certified PCE of 29.2%, one of the highest certified efficiencies to date), with 93.1% of the initial efficiency retained after 700 h of continuous operation. By stabilizing the lattice structure, this work lays a solid foundation for achieving both high efficiency and long-term durability in next-generation perovskite photovoltaics.

Fig. 1. Controlling lattice expansion via Sn-I bond strengthening.

a Chemical structures of SDS, SBS, NSA, NDS and NTS. b–d Raman spectra of the control, SDS and NTS modified films. e–g Pseudo-color maps of temperature-dependent photoluminescence (TD-PL) spectra for the control, with SDS, and with NTS films across a temperature range of 100–190 K. h Temperature dependence of the full width at half maximum (FWHM) of PL peaks for the respective films. i, j Schematic representations of lattice distortions under AIMD simulations at 10 ps for the control and films incorporating NTS. k, l Computational results for bond angle variance (BAV) and distortion index (DI) to quantify lattice distortions. m, n Photoluminescence (PL) spectra of the control and films modified with NTS under different aging conditions (0–50 h of continuous light exposure).

Fig. 2. Regulating lattice strain to suppress ion migration.

Integrated differential phase contrast (IDPC) images, geometric phase analysis (GPA) strain maps(e_xy), and fast Fourier transform (FFT) patterns of the perovskite lattice for a control, b SDS modified, and c NTS modified films after 20 h of light exposure. d Stress statistics of control, SDS modified, and NTS modified perovskite films before and after 20 h of illumination, derived from Grazing incidence X-ray diffraction (GIXRD) analysis. e Arrhenius plots of conductivity for control, SDS modified, and NTS modified perovskite films. Time-of-flight secondary ion mass spectrometry (TOF-SIMS) depth profiles of halide migration under light 40 h for f pristine perovskite film and g perovskite film with NTS.

Fig. 3. Performance and stability of NBG single-junction PSCs.

a Binding energies (E_b) of SDS and NTS with Sn, FA and I vacancy defects (V_Sn, V_FA and V_I), I interstitial defects (I_i^-) and I substituted at the Sn site (I_Sn) on the perovskite surface and their defect formation energies (E_f). Scanning electron microscopy (SEM) images of the perovskite film without illumination and after illumination for 40 h pristine perovskite film (b) and NTS perovskite film (c). Transient photovoltage (TPV) decay curves (d). Transient photocurrent (TPC) decay curves (e). f Trap density (N_t) values for control, SDS-treated, and NTS-treated Sn-Pb perovskite films determined using space-charge-limited current (SCLC) analysis. g Recombination lifetime of devices under different biases derived from the Nyquist plots (Supplementary Fig. 39). The statistical PCE of Sn-Pb PSCs with different treatments (h). J-V curves (i) of the best performing devices under control and modified with NTS. j MPP tracking of control devices and devices with NTS under 1 sun illumination in the N₂ environment. k Long-term stability test of control devices and devices with NTS Sn–Pb PSCs stored in an N₂-filled glovebox.

Fig. 4. Performance and stability of 2T PTSCs.

a Cross-section SEM image of PTSCs with NTS modification. b J-V curves of the best-performing PTSCs. c Histogram of PCEs for 50 PTSCs. d MPP tracking of control device and device with NTS under 1 sun illumination in the N₂ environment. e Long-term stability test of control device and device with NTS PTSCs stored in a N₂-filled glovebox.