Available on-demand - F.EL08.08.09
Impurity Control as a Pathway Towards Controllable, Up-Scalable Co-Evaporation of Methylammonium Perovskite Thin-Film Solar Cells
Juliane Borchert1,Ievgen Levchuk2,Lavina Snoek1,Mathias Rothmann1,Henry Snaith1,Christoph Brabec2,Laura Herz1,Michael Johnston1
University of Oxford1,Friedrich-Alexander Universität Erlangen-Nürnberg2
Show Abstract
Since their emergence in 2009 perovskites solar cells have reached a remarkable efficiency of 25.2 % [1]. Metal-halide perovskites exhibit low Shockley-Read-Hall recombination rates, high absorption coefficients across much of the solar spectrum as well as high charge-carrier diffusion lengths and mobilities [2]. These properties are ideal for a wide range of applications, including solar cells, transistors, light-emitting devices and lasers. A particularly simple and popular design for perovskite solar cells is the planar architecture, which was first fabricated using co-evaporation of methylammonium lead iodide (MAI) and lead iodide (PbI2) [3]. Co-evaporation makes it possible to deposit perovskite thin-films that are smooth, very planar and pin-hole-free over large areas [4]. This makes evaporated thin-films advantageous for the fabrication of perovskite solar cells and for detailed studies of the optoelectronic properties of the material. Furthermore, no solvents are required which makes this method fully additive and prevents damage to underlying layers. This is important both for the manufacturing of tandem solar cells and the upscaling of perovskite solar cells. While this method was initially mainly used for the deposition of MAPbI3, it has recently been extended to other perovskite materials including formamidinium lead iodide (FAPbI3) [4], triple-cation perovskites [5] and perovskites incorporating tin [6]. Despite this progress, several hurdles remain on the way to large-area co-evaporated perovskite solar cells. One issue are challenges with the evaporation of MAI [7]. Especially the rate control with conventional quartz micro balances (QMBs) does not work reliably for this material. Furthermore, it has been reported that impurities in MAI influence the film morphology and efficiency of solution-processed perovskite solar cells [8]. Therefore it is important to study the evaporation mechanics of MAI and the influence of impurities in-depth, which we set out to do in this contribution [9]. We compared two different MAIs, an impure one, and a highly purified MAI. A wide range of techniques was employed to characterise the precursors and deposited films, including nuclear magnetic resonance (NMR), infra red spectroscopy and mass spectroscopy. We were able to identify impurities in MAI and track their presence over the course of an evaporation. Furthermore, we characterised the purity of commercially available MAI and found drastic differences between manufacturers. Finally we fabricated solar cells with MAI of different purity and characterised their performance. We found that impurities critically influence the process control during the co-evaporation of perovskite thin-films. Based on this finding we give recommendations to improve the control over the evaporation and therefore the reproducibility of the process. These insights pave the way towards the upscaling of co-evaporated perovskite solar cells. [1] https://www.nrel.gov/pv/cell-efficiency.html [2] MB Johnston, LM Herz (2016) Acc. Chem. Res., 49: [3] Liu, M., Johnston, M. B., & Snaith, H. J. (2013). Nature, 501(7467), [4] Borchert, J., Milot, R. L., Patel, J. B., Davies, C. L., Wright, A. D., Martínez Maestro, L., Johnston, M. B. (2017). ACS En. Lett., 2(12), [5] Gil-Escrig, L., Momblona, C., La-Placa, M.-G., Boix, P. P., Sessolo, M., & Bolink, H. J. (2018). Adv. En. Mat., 8(14), [6] Ball, J., Buizza, L., Sansom, H., Farrar, M., Klug, M., Borchert, J., Patel, J.B., Herz, L.M., Johnston, M.B. and Snaith, H.J., 2019. ACS En. Lett. (2019) 4, [7] Borchert, J., Boht, H., Fränzel, W., Csuk, R., Scheer, R. and Pistor, P., (2015). J. of Mat. Chem. A, 3(39), [8] Levchuk, I., Hou, Y., Gruber, M., Brandl, M., Herre, P., Tang, X., Hoegl, F., Batentschuk, M., Osvet, A., Hock, R. and Peukert, W., 2016 Adv. Mat. Int., 3(22), [9] Borchert, J., Levchuk, I., Snoek, L.C., Rothmann, M.U., Haver, R., Snaith, H.J., Brabec, C.J., Herz, L.M. and Johnston, M.B., 2019. ACS AMI, 11(32)