A Design Based on a Charge-Transfer Bilayer as an Electron Transport Layer for Improving the Performance and Stability in Planar Perovskite Solar Cells

Abstract

Among the n-type metal oxide materials used in the planar perovskite solar cells, zinc oxide (ZnO) is a promising candidate to replace titanium dioxide (TiO 2 ) due to its relatively high electron mobility, high transparency, and versatile nanostructures. Here, we present the application of low temperature solution processed ZnO/Al-doped ZnO (AZO) bilayer thin film as electron transport layers (ETLs) in the inverted perovskite solar cells, which provide a stair-case band profile. Experimental results revealed that † A Design Based on Stair-case Band Alignment of Electron Transport Layer for Improving Performance and Stability in Planar Perovskite Solar Cells 1 arXiv:1708.03153v1 [physics.app-ph] 10 Aug 2017 the power conversion efficiency (PCE) of perovskite solar cells were significantly increased from 12.25 to 16.07% by employing the AZO thin film as the buffer layer.Meanwhile, the short-circuit current density (J sc ), open-circuit voltage (V oc ), and fill factor (FF) were improved to 20.58 mA/cm 2 , 1.09V, and 71.6%, respectively. The enhancement in performance is attributed to the modified interface in ETL with staircase band alignment of ZnO/AZO/CH 3 NH 3 PbI 3 , which allows more efficient extraction of photogenerated electrons in the CH 3 NH 3 PbI 3 active layer. Thus, it is demonstrated that the ZnO/AZO bilayer ETLs would benefit the electron extraction and contribute in enhancing the performance of perovskite solar cells.

Influence of Chloride/Iodide Ratio in MAPbI3-xClx Perovskite Solar Devices: Case of Low Temperature Processable AZO Sub-Layer

“…As regards ZnO, developed systems showed poor stability [16], and the attention has now shifted to aluminum doped ZnO (AZO) [17][18][19], that results in a more stable interface with perovskite [20]. Aluminium doping also causes a shift in energy of the Fermi level towards the conduction band, thus reducing AZO work function [21]. Carrier concentration and electron mobility are also increased, improving the conductivity of the material.…”

Chemically Stable Semitransparent Perovskite Solar Cells with High Hydrogen Generation Rates Based on Photovoltaic–Photoelectrochemical Tandem Cells

“…Optoelectronic properties such as conductivity, energy‐level alignment, and transmittance can be improved by inserting an appropriate interlayer to suppress charge recombination. [ 34–39 ] For instance, a PCBM interlayer effectively suppressed the thermal decomposition of the perovskite layer, enhancing its PCE from 17.5% to 19.07% due to the reduced interfacial barrier. [ 37 ] However, PCBM/ZnO showed instability due to PCBM aggregation during the annealing process, revealing the limitations of using thermally unstable organic materials as interlayers.…”

Device Physics of the Carrier Transporting Layer in Planar Perovskite Solar Cells

“…Schematic illustration of field‐effect‐induced band bending in the heterojunctions of a) ZnO/CH 3 NH 3 PbI 3 and b) ZnO/AZO/CH 3 NH 3 PbI 3 without illumination (solid blue line) and with illumination (dashed green line). Reproduced with permission . Copyright 2017, American Chemical Society.…”

“…After the incorporation of the AZO interlayer, the cascade energy level will eliminate the band bending and favor the charge separation process at the ZnO/AZO/perovskite interface compared with the ZnO/perovskite interface, which allows more electrons to be efficiently extracted from the CH 3 NH 3 PbI 3 active layer. The improved carrier extraction and suppressed interface charge carrier recombination ultimately enhanced the PCE from 12.3% to 16.1% . Another work has proposed the deposition of a thin layer of MgO on the ZnO layer to inhibit the interfacial recombination and subsequently, the further introduction of protonated ethanolamine (EA) to promote efficient electron transport from perovskite to ZnO (Figure c).…”

“…Regarding the inorganic semiconductor materials, metal oxides possess superior stability and tunable optical and electrical properties compared with the organic semiconductor materials. The various metal oxides such as titanium dioxide (TiO 2 ), zinc oxide (ZnO), and tin oxide (SnO 2 ) are commonly used as the electron transport layer (ETL), while nickel oxide (NiO x ), copper oxide (Cu 2 O), copper (I) thiocyanate (CuSCN), copper gallium oxide (CuGaO 2 ), and nickel cobalt oxide (NiCoO x ) serve as the hole transport layer (HTL) in the PVSCs . Meanwhile, several theoretical studies based on different approaches to the device models have also been reported, focusing on the underlying physics of the efficiency loss, hysteresis phenomena, etc., which are substantially affected by the carrier transport layer (CTL) properties.…”