Charge transport affected by energy level alignment in perovskite solar cells

The electron transport layer is very critical to the device performance in perovskite solar cells. In this work, we use a solution-processed method to prepare uniform Zn2SnO4, SnO2, and ZnO thin films using very similar experimental conditions. Perovskite solar cells (PSCs) based on different electron transporting layers are fabricated and compared. Three different energy level alignments produced by Zn2SnO4, SnO2, and ZnO are realized by the corresponding bandgap structures. Meanwhile, energy loss and driving force caused by the three materials are two important factors that affect charge transport. We use this system to test which factor is dominant in terms of charge transport and device performance. The optimal efficiency of PSCs based on Zn2SnO4 is 16.9%, which is much higher than SnO2 (13.4%) and ZnO (5.9%) prepared by a similar method. Therefore, we attribute the high efficiency to the reduced energy loss during charge transfer from the perovskite layer to Zn2SnO4. The large driving force of the PSC based on SnO2 and ZnO cannot achieve high efficiency. Therefore, energy loss is a dominant factor in the presence of a driving force. This work presents an understanding of the efficient charge transfer in the devices, which proposes a direction to optimize charge transfer in optoelectronic devices toward high efficiency.

Automated summary

The study utilized a solution-processed method to prepare Zn2SnO4, SnO2, and ZnO thin films as electron transport layers, with Zn2SnO4 showing higher efficiency. Energy loss was identified as one of the main factors affecting charge transport.