| Pacific Rim Symposium on Surfaces, Coatings and Interfaces (PacSurf 2016) | |
| Energy Harvesting & Storage | Tuesday Sessions |
| Session EH-TuM |
| Session: | Surfaces & Interfaces for Solar Cells and Solar Fuels |
| Presenter: | Philip Schulz, NREL, USA |
| Authors: | P. Schulz, NREL, USA A.A. Dameron, NREL, USA P.F. Ndione, NREL, USA M. Yang, NREL, USA K. Zhu, NREL, USA J.J. Berry, NREL, USA |
| Correspondent: | Click to Email |
Hybrid organic/inorganic perovskites define an emerging class of solar cell absorber materials which advances to the lead in maximum power conversion efficiencies in the area of thin-film solar cells.1 In the photovoltaic device the electronic interaction between the perovskite absorber and adjacent charge extraction and transport layers is key to maximize cell functionality. We identified that device characteristics such as the open circuit voltage can be affected by the alignment of the electronic energy levels of an organic charge extraction layer with the electronic transport levels in the perovskite film.2 Furthermore, we found that the doping characteristic of the underlying oxide substrate can be used to rigidly tailor the Fermi level position in a subsequently deposited perovskite film. For future applications such as the integration of a perovskite subcell into a tandem device, precise control over the electronic alignment processes is required.3
Here we present our recent findings in which we examine a selection of incrementally deposited oxide charge carrier transport layers on top of methylammonium and formamidinium lead iodide perovskite films. Functional n-type (e.g. TiO2, MoOx), p-type (e.g. NiO) and intrinsic oxides (e.g. Al2O3) are grown by pulsed laser and atomic layer deposition techniques on top of the perovskite absorber layer. We then use ultraviolet and X-ray photoemission spectroscopy (UPS/XPS) to determine the electronic energy level alignment at the oxide/perovskite interface while at the same time tracking changes in the interface chemistry. Using this approach we are able to explain band offset changes induced in the perovskite layer by chemical interactions with the oxide on top, changes in the electrostatic potential and the formation of defective surface layers. The results are not only used to give guidelines about how to embed oxide layers into perovskite photovoltaic devices but also inform to what extent the electronic structure of the perovskite is subject to extrinsic perturbations on a more universal scale.
[1] K. Emery, Best research‐cell efficiencies. http://www.nrel.gov/ncpv/images/efficiency_chart.jpg, Ed. NREL: 2016
[2] P. Schulz, E. Edri, S. Kirmayer, G. Hodes, D. Cahen, A. Kahn, Energy Environ. Sci.2014, 7, 1377
[3] P. Schulz. L. L. Whittaker-Brooks, B. A. MacLeod, D. C. Olson, Y.-L. Loo, A. Kahn, Adv. Mater. Interfaces 2015, 2, 1400532