Unusually Dispersed AgI Quantum Dots For Efficient HTL-Free CH₃NH₃PbI₃ Photovoltaics

The utilization of quantum dots (QDs) to improve the performance of perovskite solar cells is attracting much attention due to their unique optical and electronic properties. Most of QDs have to be prepared in advance and then incorporated into the perovskite hosts, which could not ensure the maintenance of their QD characteristics. In this work, we intelligently developed an in situ preparation strategy to disperse AgI QDs homogeneously in the perovskite host for the MAPbI₃:AgI(QDs) cross-blended layer directly on indium tin oxide (ITO) via a common and convenient spin-coating process. We combine transmission electron microscopy, X-ray photoelectron spectroscopy, and Raman techniques to demonstrate the cross-blended MAPbI₃:AgI(QDs) structure in the final perovskite devices. Furthermore, a series of simply inverted ITO/MAPbI₃:AgI(QDs)/PCBM/Ag devices have been designed and fabricated. The photovoltaic performance of these solar cells shows significantly improved short-circuit current density (J_sc) and a champion power conversion efficiency of 16.41% even without a hole transport layer. The current technique induced the crystal growth toward high-quality perovskite films with a homogeneous structure, good crystallinity, less grain boundaries and defects, increased optical path length, and uniform thickness for better solar cell performance. Besides, the impact of the current strategy also lies in an accommodation effect of the hole collection at the ITO side induced by AgI QDs, which modifies the Fermi level of perovskite films, leading to significantly decreased level difference in the Fermi level/work function between the perovskite layer and ITO substrates by ultraviolet photoelectron spectra analysis. More importantly, the charge carrier dynamics of such novel MAPbI₃:AgI(QDs) structures were also scrutinized by transient photovoltage analysis.