Charge Selective Contacts for Halide Perovskite Semiconductors

It has been well documented in previous reports that optoelectronic properties of perovskites can be altered by the substrate (or selective contact) underneath [1], however so far, we do not dispose of any conclusive picture explaining this effect. In the conventional solar cell stack, a thin perovskite layer is usually buried between charge selective layers, making it very challenging to probe its properties.<br/>Here, we fabricated a functional lateral heterojunction device, which consists of a substrate with two laterally arranged selective contacts (TiO_x as an electron transport layer and NiO_x as a hole transport layer), onto which a continuous methyl ammonium lead iodide (MAPbI₃) perovskite layer is deposited. Taking advantage of now exposed perovskite surface, we used a series of surface sensitive techniques and advanced optical characterisation techniques, such as ultraviolet and X-ray photoemission spectroscopy (UPS/XPS), X-ray absorption spectroscopy, Kelvin probe force microscopy, and hyperspectral imaging, to measure how substrate selectivity is affecting the optoelectronic properties of the perovskite.<br/>We find evidence suggesting that the contact selectivity is inducing a carrier concentration gradient in the perovskite layer across the junction connected to the functionality of the lateral device. Furthermore, we are able to show, that by varying selectivity of the contacts through different oxidation levels we can alter the magnitude of this gradient, which in turn influences built in potential within the sample and hence the device performance [2].<br/>This study provides a baseline for tailoring the selectivity of the contact materials for enhancing performance of perovskite solar cells and opening an avenue for new device architectures including buried cells terminals [3].<br/><b>_____________________</b><br/><b>Références </b><br/>1. P. Schulz, L.L. Whittaker-Brooks, B. A. MacLeod, D. C. Olson, Y.-L. Loo, A. Kahn, A. Adv. Mater. Interfaces <b>2015</b>, <i>2</i>, 1400532<br/>2. S. Dunfield, A. Bojar, et al., <i>Cell Rep. Phys. Sci..</i><b>2021</b>, <i>2, </i>100520<br/>3. D. Regaldo, A. Bojar, et al., <i>Prog. Photovolt.: Res. Appl.</i> <b>2021</b> https://doi.org/10.1002/pip.3529