Enhanced Selective Charge Collection with Metal–Insulator–Semiconductor Junction in Electron Transport Layer‐Free Perovskite Solar Cells

Abstract

Electron transport layer (ETL)‐free perovskite solar cells (PSCs) have witnessed great progress via material and interface engineering. Enlighten by the wisdom from an old story of efficient silicon solar cells design, highly efficient MINP (metal/insulator/n‐type perovskite/p‐type spiro‐MeOTAD) PSC with polar insulating inter‐layer (PIIL) modified fluorine‐doped tin oxide (FTO) is reported as electron selective contact. The PIIL forms metal‐insulator‐semiconductor (MIS) junction with FTO and perovskite layer, while the n‐type perovskite forms P‐N junction with p‐type spiro‐MeOTAD. Unlike the classic MINP silicon solar cells where the I‐layer is usually neutral tunneling layer, the PIIL here optimizes the energy level alignment at the FTO/perovskite interface with its intrinsic electronic polarity while acting as an effective tunneling layer. Also, the functional group of the PIIL passivates the FTO/perovskite interface defects thus suppressing carrier recombination thereof and enhancing all device performance parameters simultaneously. Accordingly, the power conversion efficiency is greatly improved from 12.82% to 19.75%. With the enhanced electron collection and decreased carrier recombination of the MIS junction, this collaborative effect of interface engineering and defect passivation contribute to more stable ETL‐free PSC with less hysteresis. This work highlights the potential of novel device and interface design for simple‐structured, efficient and cost‐effective PSCs.

Advances on the Application of Wide Band‐Gap Insulating Materials in Perovskite Solar Cells

“…[30] M-S contacts tend to form Schottky barriers, which are usually eliminated by forming Ohmic contacts. Therefore, for cathodes collecting electrons, we need to reduce its work function, [189] while for anodes collecting holes, we need to increase its work function to eliminate or lower Schottky barrier. [16,87] For example, Huang et al modified FTO with RbF to form a dipole layer to reduce its work function, thus eliminating the electron transport barrier and effectively blocking the hole injection (Figure 6d).…”

Perovskite Metal–Oxide–Semiconductor Structures for Interface Characterization

“…Moreover, the use of electrical measurements on MOS devices could be further extended for the study of perovskite/HTL interfaces as well. Perovskite MOS structures were not used to extract such parameters in the literature, but, instead, were used to study the hysteresis induced by ion movement; [50,51] to use the MOS structure as photodetector; [49] to use the MOS as a light-emitting diodes (PeLEDs) [55,56] and to use ETL-free PSCs, [57,58] just to name a few examples. In this work, electrical measurements will be performed on inverted MOS devices, as a proof of concept that allows to extract important interface parameters.…”

Cascaded band gap design for highly efficient electron transport layer-free perovskite solar cells

“…This makes the charge transfer and extraction at the interfaces lack driving force and the charge recombination is serious; on the other hand, the insufficient coverage and pinholes of the perovskite will lead to the ohmic contact of other layers with TCO, acting as shunt paths and causing current leakage. 10 To solve these issues, many efforts have been paid to improving the photovoltaic performance of ETL-free PSCs. One strategy is to optimize the mismatched energy level alignment by TCO modification and perovskite component engineering.…”

“…This makes the charge transfer and extraction at the interfaces lack driving force and the charge recombination is serious; on the other hand, the insufficient coverage and pinholes of the perovskite will lead to the ohmic contact of other layers with TCO, acting as shunt paths and causing current leakage. 10…”