Interface Studies of Metal Oxides Grown Directly on Hybrid Perovskite by Atomic Layer Deposition
Claire Burgess a, Farzad Mardekatani Asl a, Valerio Zardetto b, Herbert Lifka b, Sjoerd Veenstra b, Mariadriana Creatore a
a Department of Applied Physics, Eindhoven University of Technology, P.O. Box 513, 5600 MB Eindhoven, The Netherlands
b TNO - Solliance, High Tech Campus 21, 5656 AE, Eindhoven, The Netherlands
Proceedings of International Conference on Hybrid and Organic Photovoltaics (HOPV19)
Roma, Italy, 2019 May 12th - 15th
Organizers: Prashant Kamat, Filippo De Angelis and Aldo Di Carlo
Oral, Claire Burgess, presentation 166
Publication date: 11th February 2019

In the field of perovskite solar cells, atomic layer deposition (ALD) is an increasingly important tool for the deposition of metal oxides on top of perovskite. The chemical reactions of the ALD precursors with a surface allow low temperature growth of layers with unsurpassed uniformity. Moreover, the process is facile to scale, offering the choice of deposition under vacuum (conventional) or at atmospheric pressure (spatial ALD).[1] The potential value of adopting ALD for layer growth directly on perovskite was earlier established with the application of an ultrathin Al2O3 layer on methylammonium lead iodide.[2] We have recently further corroborated this by deposition of Al2O3 on wide bandgap, mixed cation, mixed halide perovskite, boosting the Voc of cells by over 100mV.[3] Next to the case study of Al2O3, several other ALD metal oxides have been successfully implemented in perovskite solar cells, among which is SnO2. It is well known that the latter, grown on perovskite with an organic interlayer between,[4] operates as both an effective electron transport layer (ETL) and as a barrier to the diffusion of chemical species through the cell. However, when ALD SnO2 is grown directly on top of perovskite, the solar cell performance is worse, although this can be mitigated to a certain degree by adjustment of the perovskite composition.[5]

In this contribution, we therefore select Al2O3 and SnO2 and report on an in-depth study of their growth behavior on (Cs,FA)Pb(I,Br)3 perovskite, with the purpose of providing insight on the chemical changes at the perovskite/metal oxide interface, responsible for poor cell performance with SnO2 but surface passivation with Al2O3.

ALD allows controlled monolayer by monolayer growth on a substrate, so through x-ray photoelectron spectroscopy, including angle resolved measurements, it is possible to study the changing composition at the perovskite interface as metal oxide is grown.[6] Exposure of the (Cs,FA)Pb(I,Br)3 perovskite to water (the shared oxygen source in our ALD processes) at a substrate temperature of less than 100° C, does not significantly affect the surface composition of the perovskite.  Instead, the precursor used as the metal source is found to be of greater consequence. For SnO2 growth (using tetrakis(dimethylamino)tin), we prove that the bulk of the (Cs,FA)Pb(I,Br)3 perovskite is unchanged compared to pristine perovskite, but at the interface between the two materials a layer consisting of some perovskite constituents (namely Pb, Br and decomposed FA) is gradually formed. Upon deposition of a layer of thickness representative of an ETL (> 10nm SnO2), it is found that the interface layer (after exposure using a peel-off technique) consists of approximately 10% decomposed FA, 70% Pb and 20% Br, and is < 1nm thick. For the growth of Al2O3 on (Cs,FA)Pb(I,Br)3 using trimethylaluminum precursor, this interface developed is thinner. To determine the factors affecting the formation of interfaces we vary deposition parameters and also compare metal sources, for example slower Al2O3 nucleation is observed with dimethylaluminum isopropoxide than trimethylaluminum precursor. The comparison of the interfaces of SnO2 and Al2O3 with perovskite, along with other contributing factors such as the band alignment, the inherently different thickness of metal oxide and cell configurations (p-i-n vs. n-i-p) employed are discussed with reference to the differing cell performance.

© Fundació Scito
We use our own and third party cookies for analysing and measuring usage of our website to improve our services. If you continue browsing, we consider accepting its use. You can check our Cookies Policy in which you will also find how to configure your web browser for the use of cookies. More info