Defect Passivation and Lithium Ion Coordination Via Hole Transporting Layer Modification for High Performance Inorganic Perovskite Solar Cells

Metal halide inorganic perovskite solar cells (PSCs) have great potential to achieve high efficiency with excellent thermal stability. However, the surface defect traps restrain the achievement of high open circuit voltage (VOC) and power conversion efficiency (PCE) of the devices due to the severe nonradiative charge recombination. Moreover, the state-of-the-art hole transporting layer (HTL) significantly hampers device moisture stability, even though it renders the highest solar cell efficiency. Herein, a one-stone-two-birds strategy is proposed using a biocompatible material tryptamine (TA) as an additive in HTL. First, TA bearing electron rich moieties can favorably passivate the surface defects of inorganic perovskite films, significantly reducing trap density and prolonging charge lifetime. It results in a drastic improvement of VOC from 1.192 to 1.251 V, with a VOC loss of 0.48 V. The corresponding PSCs achieve a 21.8% PCE under 100 mW cm-2 illumination. Second, TA in HTL can coordinate with lithium cations, retarding their reaction with moisture and increasing the moisture stability of HTL. Consequently, the black phase of inorganic perovskite films is well preserved, and the corresponding PSCs maintain 90% of the initial PCE after 800 h storage at relative humidity of 25-35%, much higher than the control devices. Tryptamine as an additive is introduced in the hole transport layer. The molecular interactions of tryptamine with perovskite and lithium cation result in a drastic improvement of VOC from 1.192 to 1.251 V, yielding a high device power conversion efficiency of 21.8%, together with greatly enhanced moisture stability.image

Automated summary

The addition of biocompatible material tryptamine (TA) in the hole transporting layer (HTL) improves surface defects and moisture stability of inorganic perovskite films in metal halide solar cells. This strategy significantly enhances the open circuit voltage and power conversion efficiency of the devices, and increases the stability of the cells in humid environments.