Metal halide perovskite solar cells have achieved efficiencies exceeding 26%, at par with crystalline Silicon. However, concerns of long-term stability and open questions about upscaled manufacturing persist. I will show how atomic layer deposition (ALD) can unlock further progress towards increased efficiency and long-term stability. Permeation barriers prepared by ALD as integral part of the device architecture suppress thermally driven decomposition of the perovskite and inhibit detrimental diffusion of halide species [1]. At the same time, ALD enables novel processing options for the preparation of semitransparent cells [2] and ultra-thin loss-less interconnects for tandem architectures [3] with the prospects to reach efficiency levels beyond 30% [4].
As ALD is originally a vacuum-based batch-processing technique, I will address the prospects of upscaling ALD for high-throughput manufacturing by the introduction of spatial ALD (S-ALD).
[1] K. O. Brinkmann et al., Nat. Comms. 2017, 8, 13938.
[2] T. Gahlmann et al., Adv. Energy Mater. 10, 1903.
[3] K. O. Brinkmann et al., Nature 604, 280 (2022).
[4] K.O. Brinkmann et al. Nat. Rev. Mater. DOI: 10.1038/s41578-023-00642-1.
Aqueous dispersions of silver nanowires state an environmentally friendly avenue for highly conductive, yet transparent top electrodes for semi-transparent perovskite solar cells. However, for the well-known chemical instability of halide perovskites upon exposure to water, there are no reports of successful aqueous processing on top of perovskite devices. Here, we show that electron extraction layers of AZO/SnOx [1,2], with the SnOx grown by low temperature atomic layer deposition, provide outstanding protection layers, which even afford the spray coating of AgNW electrodes (sheet resistance Rsh =15 Ohm/sq and a transmittance of 90%) from water-based dispersions without damage to the perovskite.
The layer sequence of the inverted cells is ITO/PTAA/perovskite/PCBM/AZO/SnOx/top-electrode. In devices without the ALD SnOx, aqueous spray processing decomposes the perovskite layers. Interestingly, the direct interface of Ag-NW/SnOx comprises a Schottky barrier, with characteristics strongly dependent on the charge carrier density of the SnOx. For a carrier density below 10^18 cm^-3, S-shaped J-V characteristics are found, that successively vanish upon UV-light soaking. For our low-T SnOx with 10^16 cm^-3, the insertion of a thin interfacial layer with a high charge carrier density (10^20 cm^-3), e.g. 10nm of ITO, is found to afford high performance semitransparent PSCs with an efficiency of 15%. Most importantly, compared to ITO electrodes Ag-NW based electrodes provide a key to achieve a higher transmittance in the IR, which is desirable for tandem Si/PSCs.
[1] K. Brinkmann et al., Nat. Commun. 8, 13938 (2017).
[2] L. Hoffmann et al. ACS Applied Mater. & Interfaces 10, 6006 (2018).
The recently re-discovered class of organometal-halide perovskites hold great promise for solar cells, LEDs and lasers.[1] Today, their potential has not been fully unlocked partially because of the lack of suitable nano-patterning techniques, which are mandatory to create resonator structures, waveguides etc. with a maximum level of precision directly into perovskite layers. Their chemical and thermal instability prevents the use of established wet-chemical patterning techniques.[2] In contrast to conventional inorganic semiconductors, crystal binding in these perovskites includes significant contributions of van der Waals interactions among the halide atoms and Hydrogen bonding.[3] The formation enthalpy per unit cell is only about 0.1eV in MAPbI3.[4] Here, we take advantage of the “soft-matter properties” of organo-metal halide perovskites and demonstrate that photonic nano-structures can be prepared by direct thermal nano-imprint lithography in MAPbI3 and MAPbBr3 at relatively low temperatures (<150°C). The resulting periodic patterns provide distributed feedback resonators, which afford lasing in MAPbI3 with ultra-low threshold levels on the order of 1 μJ/cm2.[5] Moreover, our results also state the first DFB lasers based on MAPbBr3. We will discuss the applicability of thermal imprinting for perovskite solar cells and LEDs.
[1] B. R. Sutherland et al. Nat Photon 2016, 10, 295.
[2] D. Lyashenko et al. physica status solidi (a) 2017, 214, 10.1002/pssa.201600302.
[3] D. A. Egger et al. Journal of Physical Chemistry Letters 2014, 5, 2728.
[4] A. Buin et al. Nano Lett 2014, 14, 6281.
[5] N. Pourdavoud et al. Adv Mater 2017, 10.1002/adma.201605003.
Perovskite solar cells (PSCs) suffer from decomposition of the active material in the presence of moisture or heat. In addition, the corrosion of metal electrodes due to halide species needs to be overcome.[1,2]
Here, we introduce ALD-grown tin oxide (SnOx) as impermeable electron extraction layer (EEL), which affords air resilient and temperature stable MAPbI3 PSCs. Being conductive, SnOx is positioned between the metal electrode and the perovskite. Its outstanding permeation barrier properties protect the perovskite against ingress of moisture or migrating metal atoms, while simultaneously the metal electrode is protected against leaking halide compounds.[2] Therefore, SnOx is also excellently suited to sandwich and protect ultra-thin metal layers (Ag or Cu) as cost efficient Indium-free semitransparent electrodes (SnOx/metal/SnOx) in PSCs. Using photoelectron spectroscopy, we unravel the formation of a PbI2 interfacial layer between a SnOx EEL and the perovskite. The resulting interface dipole between SnOx and the PbI2 depends on the choice of oxidant for ALD (water, ozone, oxygen plasma). SnOx grown by using ozone affords hysteresis-free devices with a stable efficiency of 16.3% and a remarkably high open circuit voltage of 1.17 V.[3] Finally, we fabricated semitransparent PSCs with efficiency >11% (Tvis = 17%) and an astonishing stability > 4500h under ambient conditions (>50% RH) or elevated temperatures (60°C).[4]
[1] Y. Kato et al., Adv. Mater. Interf. 2015, 2, 150019
[2] K. Brinkmann et al., Nat. Commun. 8, 13938
[3] T. Hu et al. Adv. Mat. (submitted)
[4] J. Zhao et al. Adv. Energ. Mat. (in press)
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