Lead-Free Perovskite Semiconductors Based on Germanium–Tin Solid Solutions: Structural and Optoelectronic Properties

Abstract

Solar cells and optoelectronics based on lead halide perovskites are generating considerable interest but face challenges with the use of toxic lead. In this study, we fabricate and characterize lead-free perovskites based on germanium and tin solid solutions, CH3NH3Sn(1–x)Ge x I3 (0 ≤ x ≤ 1). We show that these perovskite compounds possess band gaps from 1.3 to 2.0 eV, which are suitable for a range of optoelectronic applications, from single junction devices and top cells for tandems to light-emitting layers. Their thermodynamic stability and electronic properties are calculated for all compositions and agree well with our experimental measurements. Our findings demonstrate an attractive family of lead-free perovskite semiconductors with a favorable band-gap range for efficient single-junction solar cells.

Highly stable and efficient all-inorganic lead-free perovskite solar cells with native-oxide passivation

“…XPS maps (normal incidence angle) of Ge 3d (33.0 eV) and O 1s (532.0 eV) in Fig. 2c, d, respectively, of the same surface region show a strong correlation 30,31 , confirming the formation of a Ge(IV)-rich native oxide. Supplementary Fig.…”

The Physics of Light Emission in Halide Perovskite Devices

“…However, these materials have typically exhibited low PLQEs. For example, methylammonium tin iodide has a reported PLQE of 5.3%, phenethylammonium tin iodide up to 0.24%, methylammonium germanium‐tin iodide up to 2%, and methylammonium bismuth iodide ≈0.4% . There are therefore only few examples of room‐temperature electroluminescence from these materials and, in the examples that exist, the external quantum efficiency is low .…”

Lead-free hybrid perovskites for photovoltaics

“…The combination of Sn 2+ and Ge 2+ in single HPs results in solid-solution CH 3 NH 3 Sn (1− x ) Ge x I 3 compounds with a bandgap tunable from 1.3 eV ( x = 0) to 2.0 eV ( x = 1) [146]. …”