| AVS 63rd International Symposium & Exhibition | |
| Thin Film | Tuesday Sessions |
| Session TF-TuA |
| Session: | Thin Film Photovoltaics |
| Presenter: | Mariadriana Creatore, Eindhoven University of Technology, Netherlands |
| Authors: | V. Zardetto, Eindhoven University of Technology, Netherlands F. di Giacomo, Solliance/TNO, Netherlands R. Andriessen, Solliance/TNO, Netherlands T.M. Brown, University of Rome “Tor Vergata”, Italy A. di Carlo, University of Rome “Tor Vergata”, Italy W.M.M. Kessels, Eindhoven University of Technology, Netherlands M. Creatore, Eindhoven University of Technology, Netherlands |
| Correspondent: | Click to Email |
Within the class of emerging photovoltaic technologies, organo-metal halide perovskite solar cells have exhibited a sky-rocketing conversion efficiency above 20% in just a few years. In this contribution we will address the opportunities which ALD offers to perovskite solar cells by highlighting its merits of low temperature processing and compatibility with 3D-structures.
Specifically, we will present two studies aimed at the suppression of charge carrier recombination processes at the complex interface ITO/mesoscopic TiO2 scaffold/ mixed halide perovskite absorber.
In the first study we investigate the role of thin plasma-assisted ALD TiO2 blocking layers on PET/ITO substrates, developed at a substrate temperature of 150°C [1,2]. The ALD TiO2 layer is found to exhibit an excellent blocking behaviour towards charge carrier recombination at the above-mentioned interface, leading to open circuit voltage (Voc) values as high as 900 mV (with respect to the pristine PV device exhibiting no rectifying behaviour with a Voc of 50 mV) and superior device performance (9.2%) with respect to a sol-gel TiO2 blocking layer (4%).
In the second example we carry out few ALD cycles of Al2O3 in a 250 nm-thick mesoscopic TiO2 scaffold. Next to the conformality of the process, we demonstrate by means of electrochemical impedance spectroscopy that just one ALD cycle is sufficient to suppress the charge recombination processes. Specifically, the Voc is found to increase from 860 to 960 mV upon 1 ALD cycle of Al2O3.
This contribution will end by discussing the challenges yet to be met by ALD processing directly on perovskite. In all these cases, a careful interface engineering needs to include several aspects potentially affecting the opto-chemical and morphological stability of the active components of the device. For example, methylammonium lead iodide perovskite solar cells already degrade under prolonged (i.e. few hours) annealing at 80°C, as witnessed by the appearance of a PbI2-related peak in the XRD spectrum. However, when the Al2O3 plasma-assisted ALD process at 30°C is compared with the thermal process at 80°C, the plasma step is found to be responsible for abstraction of the methylammonium cation and the formation of iodate species. Instead, the thermal ALD process does not affect the chemistry of the perovskite. These selected examples point out that processing temperature and choice of reactant (moisture or plasma radicals) need to be carefully considered when dealing with processing of hybrid materials, such as perovskite solar cells.
[1] F. Di Giacomo et al., Adv. Energy Mat. 5, 1401808 (2015)
[2] V. Zardetto et al., ECS Transactions 69 (7), 15 (2015)