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

TL;DR

The paper addresses trap-state limitations in perovskite solar cells and proposes an all-inorganic hole-only device (ITO/NiO_x/Perovskite/CIS/Au) to enable straightforward SCLC-based trap-density measurements. By comparing pristine and TEOS-modified perovskite films, the study shows preserved crystallinity and optical properties but reduced trap density due to amorphous silica passivation, which correlates with higher fill factors and overall efficiency. The approach demonstrates a simple, stable platform for quantifying trap densities and connects defect passivation to tangible performance gains in PSCs. This work offers a practical route to diagnose and improve perovskite layer quality, with implications for device stability and manufacturability.

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.

Figures (6)

• Figure 1: SEM image of perovskite (PS) layer. The scale bar represents 500 nm.
• Figure 2: X-ray diffraction (XRD) patterns of pristine and TEOS-modified perovskite films deposited on FTO-coated glass substrates. Diffraction peaks corresponding to the perovskite phase, residual PbI$_2$, and FTO are labeled with $\alpha$, *, and #, respectively.
• Figure 3: UV--vis absorption spectra of pristine and TEOS-modified perovskite layer.
• Figure 4: J--V characteristics of perovskite solar cells incorporating pristine and TEOS-modified perovskite layers.
• Figure 5: Photoluminescence emission spectra of pristine Cs$_{0.05}$(MA$_{0.17}$FA$_{0.83}$)$_{0.95}$Pb(I$_{0.83}$Br$_{0.17}$)$_3$ perovskite (PS) films and TEOS-modified PS films.