  One of the most critical challenges in soaring the performance of perovskite
solar cells is decreasing the density of trap states in the light-absorbing
perovskite layer. These traps cause an increase in the recombination of charge
carriers and decrease the efficiency of devices. One of the methods to study
the trap density is space charge limited current (SCLC) analysis. For this
purpose, some structures are needed with the ability to transport only
electrons or holes. The trap density can be calculated by investigating the
current-voltage diagram and finding the voltage corresponding to the slope
change point. One of the challenges in these structures is using organic
polymers like Spiro-OMeTAD, PEDOT: PSS, and PTAA as hole transport layers. They
have problems like high acidity, lack of stability against moisture, low charge
mobility, low conductivity, and high cost. In this work, a hole-only device
structure is explained, made based on inorganic materials, which possesses high
stability, a simple preparation method, and reasonable cost compared to
conventional hole-only device structures. This structure is built by coating a
nanostructured NiOx layer, perovskite, CIS, and Au on the ITO substrate. To
investigate the performance of this structure, various perovskite layers were
made at different experimental conditions, and their trap density was obtained
by the proposed hole-only device structure. The analysis of the photovoltaic
characteristics of cells revealed a clear correlation between the perovskite
layer's trap density and the cells' performance. Our results show the
introduced structure is a simple and stable structure that can be utilized in
studying the trap density in perovskite layers to make more efficient cells.
