Strontium-Doped Low-Temperature-Processed CsPbI₂Br Perovskite Solar Cells

Cesium (Cs) metal halide perovskites for photovoltaics have gained research interest due to their better thermal stability compared to their organic–inorganic counterparts. However, demonstration of highly efficient Cs-based perovskite solar cells requires high annealing temperature, which limits their use in multijunction devices. In this work, low-temperature-processed cesium lead (Pb) halide perovskite solar cells are demonstrated. We have also successfully incorporated the less toxic strontium (Sr) at a low concentration that partially substitutes Pb in CsPb_1–<i>x</i>Sr_<i>x</i>I₂Br. The crystallinity, morphology, absorption, photoluminescence, and elemental composition of this low-temperature-processed CsPb_1–<i>x</i>Sr_<i>x</i>I₂Br are studied. It is found that the surface of the perovskite film is enriched with Sr, providing a passivating effect. At the optimal concentration (<i>x</i> = 0.02), a mesoscopic perovskite solar cell using CsPb_0.98Sr_0.02I₂Br achieves a stabilized efficiency at 10.8%. This work shows the potential of inorganic perovskite, stimulating further development of this material

Water-Free, Conductive Hole Transport Layer for Reproducible Perovskite–Perovskite Tandems with Record Fill Factor

State-of-the-art perovskite–perovskite tandem solar cells incorporate a water-based poly(3,4-ethylenedioxythiophene):polystyrenesulfonate (PEDOT:PSS) hole transport layer in its low bandgap subcell. However, there is a limitation regarding its use due to the moisture sensitivity of perovskites and the insulating property of PSS. Here, we overcome the limitation by using a water-free and PSS-free PEDOT-based hole transport layer for low bandgap single-junction perovskite solar cells and in perovskite–perovskite tandems. The champion tandem cell produces an efficiency of 21.5% and a fill factor of 85.8%, the highest for any perovskite-based double-junction tandems. Results of photoelectron spectroscopy, Fourier-transform infrared spectroscopy, and conductive atomic force microscopy reveal evidence of enhanced conductivity of water-free and PSS-free PEDOT compared to its conventional counterpart. The use of water-free and PSS-free PEDOT also eliminates decomposition of high bandgap subcell with its interfacing layer stack in a tandem that otherwise occurs with conventional PEDOT:PSS. This leads to enhanced reproducibility of perovskite–perovskite tandems