Three-dimensional organic–inorganic perovskites have emerged as one of the most promising thin-film solar cell materials owing to their remarkable photophysical properties1, 2, 3, 4, 5, which have led to power conversion efficiencies exceeding 20 per cent6, 7, with the prospect of further improvements towards the Shockley–Queisser limit for a single‐junction solar cell (33.5 per cent)8. Besides efficiency, another critical factor for photovoltaics and other optoelectronic applications is environmental stability and photostability under operating conditions9, 10, 11, 12, 13, 14, 15. In contrast to their three-dimensional counterparts, Ruddlesden–Popper phases—layered two-dimensional perovskite films—have shown promising stability, but poor efficiency at only 4.73 per cent13, 16, 17. This relatively poor efficiency is attributed to the inhibition of out-of-plane charge transport by the organic cations, which act like insulating spacing layers between the conducting inorganic slabs. Here we overcome this issue in layered perovskites by producing thin films of near-single-crystalline quality, in which the crystallographic planes of the inorganic perovskite component have a strongly preferential out-of-plane alignment with respect to the contacts in planar solar cells to facilitate efficient charge transport. We report a photovoltaic efficiency of 12.52 per cent with no hysteresis, and the devices exhibit greatly improved stability in comparison to their three-dimensional counterparts when subjected to light, humidity and heat stress tests. Unencapsulated two-dimensional perovskite devices retain over 60 per cent of their efficiency for over 2,250 hours under constant, standard (AM1.5G) illumination, and exhibit greater tolerance to 65 per cent relative humidity than do three-dimensional equivalents. When the devices are encapsulated, the layered devices do not show any degradation under constant AM1.5G illumination or humidity. We anticipate that these results will lead to the growth of single-crystalline, solution-processed, layered, hybrid, perovskite thin films, which are essential for high-performance opto-electronic devices with technologically relevant long-term stability.
At a glance
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Extended data figures and tables
Extended Data Figures
- Extended Data Figure 1: Layered perovskite thin-film morphology and device performance. (743 KB)
a, b, AFM images of surface morphology for room-temperature-cast (a) and hot-cast (b) films. Scale bars, 400 nm. c, d, SEM images of topography for room-temperature-cast (c) and hot-cast (d) films. Scale bars, 1 μm. e, J–V curve of Pb4I13 with C60 as a contact modification candidate shows the enhancement of VOC from 0.9 V to 1.055 V with the same device architecture. f, J–V curve for the (BA)2(MA)3Pb4I13 device using the room-temperature (RT) spin-cast method. FF, fill factor.
- Extended Data Figure 2: Absorption spectroscopy of layered 2D perovskites. (208 KB)
a–c, Local optical absorption characteristics of thin films using reflection/transmission experimental methods (see also refs 34, 35 for details of the modelling): results of the fitting of the reflection (R) and transmission (T) data (a); absolute absorption cross-section (b); and real (n; red line) and imaginary (k; black line) parts of the refractive index (c). d, Absorbance of thin films (grey circles) compared to that of optimized solar cells (red squares) measured using integrating sphere techniques (see details in ref. 36).
- Extended Data Figure 3: DFT computation. (124 KB)
a, b, Electronic band structures of (BA)2PbI4 (n = 1; a) and (BA)2(MA)2Pb3I10 (n = 3; b) calculated using DFT with a local-density approximation, including the spin–orbit coupling and a bandgap correction computed using the HSE (Heyd–Scuseria–Ernzerhof) functional. The energy levels are referenced to the valence band maximum.
- Extended Data Figure 4: Device performance of (BA)2(MA)2Pb3I10. (202 KB)
a, J–V curve and device parameters. b, EQE (red circles) and integrated JSC from EQE (blue dashed line).
- Extended Data Figure 5: Dark current transient and mobility. (194 KB)
The dark current transient (ΔJ/J0), measured using the CELIV technique, for a hot-cast (red) and a room-temperature-cast (‘As cast’, black) device, and the mobility value (μ) in each case.
- Extended Data Figure 7: Hysteresis tests for 2D pervoskite devices. (330 KB)
a–d, Tests with different bias sweep directions (a; (C/C0)−2 as function of DC bias, where C0 is the capacitance of a geometric capacitor), and after 10 h (b), 1,000 h (c) and 2,250 h (d) of constant illumination. The red and blue arrows indicate the forward and reverse sweep directions.
- Extended Data Figure 8: Simulation results and comparison of room-temperature-cast and hot-cast methods. (331 KB)
a, Experimental (‘Expr.’) J–V characteristics of room-temperature-cast (‘As cast’) and hot-cast methods and corresponding simulation (‘Sim.’) results. The hot-cast method shows a current density with a larger magnitude and higher fill factor (area below the J–V curve). b, Integrated recombination inside three layers of a solar cell. Peak recombination shifts toward the PCBM/perovskite interface because the barrier for generated carriers is less in the hot-cast case than in the room-temperature-cast case. c, d, Energy band diagram of hot-cast (c) and room-temperature-cast (d) methods. Generated carriers face a lower barrier in the hot-cast case, especially close to the PEDOT/perovskite interface. EC, conduction band; EV, valence band; EFN, electron quasi-Fermi level; EFP, hole quasi-Fermi level.
- Extended Data Figure 9: Heat stress tests. (159 KB)
a, b, Spectra of 2D (a) and 3D (b) perovskite thin films under 80 °C in darkness after the lengths of time indicated (spectra are offset for clarity; ‘ref.’ refers to freshly made thin film, measured after 0 h of heat stressing). c, Ratio of the PbI2 (2θ = 12.7°) and perovskite (2θ = 14.2°) main peaks in the spectra in a and b for the two perovskite materials (2D, blue; 3D, red) over 30 h of heating at 80 °C.
- Supplementary Information (401 KB)
This file contains a Supplementary Discussion, Supplementary Tables 1-4 and Supplementary References.