Abstract
Recently, the 2D perovskite layer is employed as a capping/passivating layer in the perovskite solar cells (PSCs). The 2D perovskite layer is prepared by inserting a large-sized hydrophobic cation spacer into the perovskite crystal lattice. The large-sized cation in the 2D perovskite lattice can successfully suppress the moisture intrusion and hence improve the stability of the PSCs. However, a deep understanding of the interfacial mechanisms at the 2D/3D heterojunction and the relative contributions of the mobile ions and trapped charge carriers is still lacking. In this work, deep levels transient spectroscopy (DLTS) and reverse DLTS (RDLTS) have been performed to characterize the n-i-p structured 3D and 2D/3D PSCs. DLTS and RDLTS have been used to distinguish between the spectral contribution made by mobile ionic species, electron/hole traps, and to investigate the presence of ordinary deep electron and hole traps in the bandgap of perovskite. Besides, the PSCs have been characterized by photoinduced voltage transient spectroscopy (PIVTS) to study the decay of the open-circuit voltage (VOC) under illumination. For both 3D and 2D/3D PSCs, the contribution of mobile ions was found to be dominant; however, in the case of 2D/3D samples, the intensity of the mobile ions signal was several times lower. The lower intensity can be correlated with a lower amplitude of slow tails in VOC decay curves in 2D/3D solar cells as compared to 3D solar cells. The PIVTS study also endorses the 2D/3D structures as more robust than the 3D structures.
Highlights
Hybrid organic-inorganic perovskite materials with structural for mula ABX3 are rapidly progressing candidates for the fabrication of costeffective solar cells
It can be seen that in good agreement with the data of Table 1, the short circuit photocurrent ISC, the VOC values and the magnitude of hysteresis in I–V characteristics were similar for both samples and close to the measurements results presented in Table 1, but with ISC and VOC consistently slightly higher for the 2D/3-dimen sional (3D) samples
The results suggest that the films are n-type and that the high-frequency plateau in capacitance versus fre quency (C-f) characteristics in Fig. 4 corresponds to the depletion of the bulk region of the films up to the accumulation region near the electron transport layer (ETL), with the band bending determined by the built-in voltage of the hole transport layer (HTL)/ perovskite heterojunction which is similar to the open-circuit voltage VOC of the I–V characteristics measured under illumination
Summary
Hybrid organic-inorganic perovskite materials with structural for mula ABX3 are rapidly progressing candidates for the fabrication of costeffective solar cells These perovskite materials possess interesting properties, such as tunable bandgaps, high absorption coefficient, large diffusion length of charge carriers, and high tolerance to defects [1]. The most successful method implemented (by Nazeeruddin group) [16] produced the power conversion efficiency (PCE) of 20.75% This method involves the depositing of a bulk organic cation on a pre-formed 3D perovskite surface to induce the in-situ growth of a 2D layer, forming a heterostructure [15,17]. It was very interesting to assess the relative importance of the mobile ions contribution and charge trapping/emission via usual deep centers in the forbidden gap in such heterostructures
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