Revealing the charge carrier kinetics in perovskite solar cells affected by mesoscopic structures and defect states from simple transient photovoltage measurements

Abstract

This report shows that, by using simple transient photovoltage (TPV) measurements, we can reveal a significant correlation between the TPV decay characteristics and the performance of these perovskite solar cells. TPV decay seems to be composed of a rising part in a short interval after photoexcitation and a long decaying part that extends up to tens of milliseconds. These decay behaviors look different depending on the mesoscopic structures and the perovskite morphology formed therein, as seen from their Scanning Electron Microcopy images and X-ray diffraction patterns. The decay part can be fitted with a three-exponential decay, which reflects different kinetics of electrons in the perovskite/TiO2 layer. On the other hand, the rising part must be fit by a decay equation derived by employing the convolution theorem, where the rising part can be assigned to the electron transport process inside the perovskite layer and the decaying part can be assigned to electron back-transfer. The characteristics can be then understood by considering the effect of crystal defects and trap states in the perovskite grains and perovskite interface with its transport layer, which is TiO2 in this study. Although the TPV decay occurs in a time range much longer than the primary process of photoexcitation as commonly observed in transient photoluminescence spectroscopy, the processes involved in this TPV strongly correlates with the performance of these perovskite solar cells.

Efficiency and Stability Enhancement of Perovskite Solar Cells Utilizing a Thiol Ligand and MoS2 (100) Nanosheet Surface Modification

“…The data henceforth were extrapolated by a biexponential decay function according to the previous reports. 48,49 The results that are depicted in Figure S19 indicate the increase of both time constants (τ 1 , τ 2 ) 49 for the devices with DTMoS 2 and MoS 2 . The results agree with SCLC and MS analyses, which also suggested the decrease of interface states and therefore reduced recombination for the devices with DTMoS 2 and MoS 2 .…”

“…To investigate the recombination in MoS 2 - and DTMoS 2 -modified devices, square-wave modulated transient photovoltage decay under different light intensities were measured at the frequency of 2 Hz. The data henceforth were extrapolated by a biexponential decay function according to the previous reports. , The results that are depicted in Figure S19 indicate the increase of both time constants (τ 1 , τ 2 ) for the devices with DTMoS 2 and MoS 2 . The results agree with SCLC and MS analyses, which also suggested the decrease of interface states and therefore reduced recombination for the devices with DTMoS 2 and MoS 2 .…”

High‐Performance Ternary Perovskite–Organic Solar Cells

“…To lessen the unbalanced character of charge transport, our strategy has been to incorporate n-type, low-optical-gap O6T-4F [34][35][36] molecules (see molecular structure in Scheme 1B) into 2D:3D mixed perovskite composites, which leads to the formation of ternary perovskite-organic composites. Scheme 1C illustrates the formation of the ternary quasi-2D (4F-BEA) x (MAPbI 3 ) 1−x :3D MAPbI 3 :O6T-4F composites.…”

“…The photoresponse at λ > 800 nm is attributed to efficient charge transport through the percolation pathways provided by O6T-4F. [34,35,40,42] Moreover, the significantly enhanced EQE in the NIR region is the signature of efficient exciton dissociation and charge transfer across the ternary active layers. The integrated photocurrents from the EQE spectra are consistent with the J SC values observed from the J-V curves (Figure 3A).…”

From Frequency Domain to Time Transient Methods for Halide Perovskite Solar Cells: The Connections of IMPS, IMVS, TPC, and TPV

“… 3 − 7 Meanwhile, time-domain measurements of the transient photocurrent (TPC) and transient photovoltage (TPV) in response to a short light pulse have also been widely reported and applied to derive fundamental parameters such as the electron lifetime. 8 − 14 The interpretation of data obtained by these methods in the area of PSCs is often very complicated, in particular by the influence of slow ionic motion that causes polarization at the interfaces. Accordingly, a number of unexpected phenomena like negative spikes in TPC and TPV 8 − 13 were explained with sophisticated physical models.…”