Temperature-dependent studies of excitors binding energy and phase-transition suppress on in (Cs,FA,MA)Pb(I,Br)(3) perovskites

Rut, Fabian; Aygueler, Lieitem F.; Giesbrecht, Nadja; Rendenbach, Bettina; Magin, Alice; Docampo, Pablo; Kait, Heinz und Hetterich, Michael (2019): Temperature-dependent studies of excitors binding energy and phase-transition suppress on in (Cs,FA,MA)Pb(I,Br)(3) perovskites. In: Apl Materials, Bd. 7, Nr. 3, 031113

Abstract

Multiple-cation mixed-halide (Cs,FA,MA)Pb(I,Br)(3) perovskites containing cesium, formarnidinium (FA), and methylammonium (MA) possess excellent properties for a wide range of optoelectronic applications such as thin-film pliotovoltaics or lasers. We investigate the role of excitons and the excitor) binding energy E-B, relevant for the effectiveness of charge separation in solar cells, as well as the temperature dependent bandgap energy E-g which is used as an indicator for crystal phase transitions. Generalized Elliott fits of absorption spectra offer the possibility to determine both E-B and E-g. However, since excitonic effects are non-negligibk even at room temperature, a careful and detailed analysis of the spectra is crucial for a correct interpretation. Therefore, an additional evaluation based on a so-called f-sum rule is applied to achieve an improved reliability of the results at higher temperatures. The obtained EB values of 20-24 meV for Cs-contailaing mixed perovskite compounds are below the ones of 24-32 meV and 36-41 meV for pure methylammonium lead iodide (MAPbI(3)) and bromide (MAPbBr(3)), respectively, and, thus, facilitate charge-carner separation in photovoltaic applications. Furthermore, temperature-dependerit (T = 5-300 K) studies of E-g in (Cs,FA,MA)Pb(I,BrP)(3) indicate a suppressed crystal phase transition by the absence of any phase-transition related signatures such as the well-Imown jump of about 100 meV in MAPbI(3). We verify these results using temperature-dependent electroreflectance spectroscopy, which is a very reliable technique for the direct and non-destructive determination of optical resonances of the absorber layer in complete solar cells. Additionally, we confirm the suppression i of the phase transition in Cs-0.05(FA(0.83)MA(0.17))(0.95)Pb(I0.83Br0.17)(3) by ternperature-deperiderit X-ray diffraction. (C) 2019 Author(s).

• Dokumententyp: Zeitschriftenartikel
• Fakultät: Physik
• Fakultätsübergreifende Einrichtungen: Center for NanoScience (CENS)
• Themengebiete: 500 Naturwissenschaften und Mathematik > 530 Physik ; 500 Naturwissenschaften und Mathematik > 500 Naturwissenschaften
• ISSN: 2166-532X
• Sprache: Englisch