30% efficient triple-cation perovskite solar cells under indoor illumination enabled by rare earth EuCl₃ doping

The huge market for Internet of Things (IoT) devices brings unprecedented opportunities for indoor photovoltaics (PV). Perovskite solar cells (PSCs) are one of the best candidates owing to their outstanding low-light conversion capability. However, their performance still suffers from trap-assisted recombination in cells, especially under low light levels. Here, for the first time, we developed and comprehensively investigated the impact of EuCl3 doping on the indoor PV performance of triple-cation (bandgap of 1.58 eV) n-i-p PSCs at various lux (lx) illuminance levels. EuCl3 doping reduced both volatile iodine (I)(0) species and unreacted residual PbI2, resulting in the formation of larger perovskite grains, more uniform films and fewer defects. Leakage currents were more than ten times lower resulting in suppressed carrier recombination and increased shunt resistance, with doubling of carrier lifetimes. Finally, the indoor power conversion efficiency (PCE) jumped to 25.0% from 22.8% at 200 lx, and to 30.0% from 27.4% at 1000 lx with the incorporation of EuCl3. Furthermore, under the thermal stress test at 85 & DEG;C, t(50) (the time at which PCE halves) was more than double that of cells fabricated without EuCl3. This work opens up new avenues for realizing efficient and stable indoor PSCs for Internet of Things applications.