Experiments showed that monocrystals of lead-halide perovskites made from aqueous solutions or from cost-effective solvents have the same quality like the cadmium telluride semiconductors in use today – whereas the production process for the latter is far more complex and thus expensive.
Nevertheless, the new solution was not an easy one, explains Maksym V. Kovalenko, professor at ETH Zurich and research team leader at EMPA. The reason: It is rather difficult to identify suitable substances; crystals to be used to detect gamma rays at ambient temperature need to have a very high electronic quality, that is, the charge carriers in the crystal must have a very high mobility and a long lifetime to be able to reliably transmit the signal as an electric impulse. In addition, in order to be able to catch the high-energy gamma radiation, the crystal must consist of heavy elements. Last but not least it must be possible to grow large monocrystals from the desired material, and these crystals must me insensitive against cracks and temperature variations.
Hitherto in the first place cadmium telluride (CdTe) was known to meet these requirements. The material also used to produce thin film solar cells is not soluble in water and needs temperatures above 1000°C to melt. These properties make production of detector crystals very expensive and complex. Kovalenko and his team now succeeded in creating semiconductor crystals of a complete different materials class (lead-halide perowskites) in classical beakers chemistry. The highly sensitive detector crystals can visualize gamma rays at a price of just a few bucks per crystal, the research team reported in “Nature Photonics”.