A simple all-inorganic hole-only structure for trap density measurement in perovskite solar cells

Abstract

One of the critical challenges in enhancing the performance of perovskite solar cells is reducing the density of trap states in the light-absorbing perovskite layer. These trap states lead to increased charge carrier recombination, thus dropping device efficiency. Space charge limited current (SCLC) analysis serves as a valuable method to study trap density, requiring structures capable of selectively transporting either electrons or holes. By analyzing current-voltage (I-V) characteristics and identifying the voltage at which the slope changes, trap density can be calculated effectively. Traditional organic polymer hole transport layers such as Spiro-OMeTAD, PEDOT: PSS, and PTAA face challenges, including moisture instability, low charge mobility, low conductivity, and high costs. This work introduces a novel hole-only device structure utilizing inorganic materials, offering improved stability, straightforward fabrication, and reduced costs compared to conventional structures. This device comprises a nanostructured NiOx layer, a perovskite layer, a copper indium selenide (CIS) layer, and an Au electrode on an ITO substrate. The performance of this structure is assessed by fabricating various perovskite layers under different experimental conditions. The trap density was successfully determined using the proposed hole-only device structure. Analysis of the photovoltaic properties revealed a clear correlation between trap density in the perovskite layers and the overall performance of the solar cells.