Cs4CuSb2Cl12−x I x (x = 0–10) nanocrystals for visible light photodetection

Abstract

Lead-free layered double perovskite nanocrystals (NCs) with tunable visible range emission, high carrier mobility and low trap density are the need of the hour to make them applicable for optoelectronic and photovoltaic devices. Introduction of Cu2+ in the high band gap Cs3Sb2Cl9 lattice transforms it to the monoclinic Cs4CuSb2Cl12 (CCSC) NCs having a direct band gap of 1.96 eV. The replacement of 50% Cl− by I− ions generates <5 nm Cs4CuSb2Cl6I6 (C6I6) monodispersed NCs with an unchanged crystal system but with further lowering of the band gap to 1.92 eV. The p-type C6I6 NCs exhibit emission spectra, lower trap density, appreciable hole mobility and most importantly a lower exciton binding energy of only 50.8 ± 1.3 meV. The temperature dependent photoluminescence (PL) spectra of the C6I6 NCs show a decrease in non-radiative recombination from 300 K down to 78 K. When applied as the photoactive layer in out-of-plane photodetector devices, C6I6 NC devices exhibit an appreciable responsivity of 0.67 A W−1 at 5 V, detectivity of 4.55 × 108 Jones (2.5 V), and fast photoresponse with rise and fall time of 126 and 94 ms, respectively. On the other hand, higher I- substitution in Cs4CuSb2Cl2I10 NCs (C2I10) degrades the lattice into a mixture of monoclinic and trigonal crystal phases, which also lowers the device performance.