Wide-bandgap perovskites for multijunction solar cells: improvement of crystalline quality of Cs0.1FA0.9PbI1.4Br1.6 by using lead thiocyanate

Abstract

Top cells based on mixed iodide-bromide lead perovskites (Cs0.1FA0.9PbI1.4Br1.6) for multijunction solar cells (MJ SCs) were fabricated and characterized. Various lead thiocyanate (Pb(SCN)2) concentrations (0%, 1%, 2%, 3%, and 4%) were added into perovskite precursor solution to fabricate high quality Cs0.1FA0.9PbI1.4Br1.6 thin films. The bandgap energy of Pb(SCN)2-added Cs0.1FA0.9PbI1.4Br1.6 thin films was 1.87 eV determined from Tauc plots. The average grain size of the 2% Pb(SCN)2-added perovskite thin film was 2.27 μm, more than 16 times larger than that of the perovskite thin film without Pb(SCN)2 (0.134 μm). The intensity of the two main peaks (14.38° and 28.97°) was intensified with Pb(SCN)2-added perovskite thin films. The photoluminescence (PL) revealed higher intensity of perovskite thin films with Pb(SCN)2 due to a decrease in nonradiative recombination. The carrier lifetimes of Cs0.1FA0.9PbI1.4Br1.6 thin films sharply increased with the presence of Pb(SCN)2, from 25.92 ns at 0% Pb(SCN)2 to 224.27 ns at 2% Pb(SCN)2. The thickness of a Cs0.1FA0.9PbI1.4Br1.6-based absorber layer cell is 400 nm which is thin enough to obtain both high transparency and large current density. As a result, the addition of 2% of Pb(SCN)2 to the precursor of Cs0.1FA0.9PbI1.4Br1.6 perovskite solar cells resulted in a notable improvement in power conversion efficiency (PCE), increasing from 9.37% to 13.66%. This improvement was accompanied by a significant increase in both open-circuit voltage (Voc), which reached 1.27 V, and current density (Jsc,JV), which reached 14.19 mA cm−2 © 2023 The Royal Society of Chemistry.