B-Site Co-Alloying with Germanium Improves the Efficiency and Stability of All-Inorganic Tin-Based Perovskite Nanocrystal Solar Cells

Colloidal lead-free perovskite nanocrystals have recently received extensive attention because of their facile synthesis, the outstanding size-tunable optoelectronic properties, and less or no toxicity in their commercial applications. Tin (Sn) has so far led to the most efficient lead-free solar cells, yet showing highly unstable characteristics in ambient conditions. Here, we propose the synthesis of all-inorganic mixture Sn-Ge perovskite nanocrystals, demonstrating the role of Ge2+ in stabilizing Sn2+ cation while enhancing the optical and photophysical properties. The partial replacement of Sn atoms by Ge atoms in the nanostructures effectively fills the high density of Sn vacancies, reducing the surface traps and leading to a longer excitonic lifetime and increased photoluminescence quantum yield. The resultant Sn-Ge nanocrystals-based devices show the highest efficiency of 4.9 %, enhanced by nearly 60 % compared to that of pure Sn nanocrystals-based devices.

The Role of Thickness Control and Interface Modification in Assembling Efficient Planar Perovskite Solar Cells

Perovskite solar cells (PSCs) have achieved tremendous success within just a decade. This success is critically dependent upon compositional engineering, morphology control of perovskite layer, or contingent upon high-temperature annealed mesoporous TiO₂, but quantitative analysis of the role of facile TiCl₄ treatment and thickness control of the compact TiO₂ layer has not been satisfactorily undertaken. Herein, we report the facile thickness control and post-treatment of the electron transport TiO₂ layer to produce highly efficient planar PSCs. TiCl₄ treatment of TiO₂ layer could remove the surface trap and decrease the charge recombination in the prepared solar cells. Introduction of ethanol into the TiCl₄ aqueous solution led to further improved open-circuit voltage and short-circuit current density of the related devices, thus giving rise to enhanced power conversion efficiency (PCE). After the optimal TiCl₄ treatment, PCE of 16.42% was achieved for PSCs with TiCl₄ aqueous solution-treated TiO₂ and 19.24% for PSCs with TiCl₄ aqueous/ethanol solution-treated TiO₂, respectively. This work sheds light on the promising potential of simple planar PSCs without complicated compositional engineering and avoiding the deposition and optimization of the mesoporous scaffold layer.