Determination of dominant recombination site in perovskite solar cells through illumination‐side‐dependent impedance spectroscopy

Abstract

Perovskite solar cells (PSCs) have attracted wide attention due to their capacity to achieve high‐power conversion efficiencies. However, the high trap‐assisted recombination taking place in the active layer leads to performance loss in PSCs. In particular, the excessive recombination at the interface between the perovskite active layer and the carrier selective contacts can be especially problematic. Therefore, the identification of the dominant recombination pathways in a given PSC architecture is of significant importance for the mitigation of losses and enhancement of device performance. Here, we introduce an approach for identifying the dominant recombination pathways in PSCs by applying illumination‐side‐dependent impedance spectroscopy (ISD‐IS) measurements on the devices with a semi‐transparent top electrode. We validate this technique using coupled ionic‐electronic numerical simulations and apply it experimentally on a standard PSC structure. Overall, this approach could be of significant importance for pinpointing the performance bottlenecks in PSC devices under operationally relevant conditions and providing a more detailed picture of the losses in a complete PSC device by examining its behaviors under illumination from both sides at different operation conditions, which could allow for a more targeted optimization strategy of PSCs to improve their performance.

Identification of Asymmetric Interfacial Recombination in Perovskite Solar Cells through Impedance Spectroscopy

“…An R eh value close to or equal to 1 indicated that either the bulk recombination is dominant or that both perovskite interfaces have the same recombination rate. The more the R eh value increases above 1, the more the HTM interface recombination would dominate, and the more it decreases below 1, the more the ETM interface recombination would dominate . It can be seen from Figure that under OC conditions there is a significant difference between the Nyquist plots of the device measured under illumination from each side.…”

“…The more the R eh value increases above 1, the more the HTM interface recombination would dominate, and the more it decreases below 1, the more the ETM interface recombination would dominate. 18 It can be seen from Figure 3 that under OC conditions there is a significant difference between the Nyquist plots of the device measured under illumination from each side. It is seen that when the device is illuminated from the c-TiO 2 side, a higher rate of recombination in the device is present, as suggested by the smaller semicircle and the smaller recombination resistance value R (see Table S1).…”

“…17 In a previous work, we presented the use of an illuminationside-dependent impedance spectroscopy (ISD-IS) measurement to identify the dominant recombination site in PSCs and examine the quality of the perovskite interface with the CTMs in fully functioning devices. 18 In this approach, the impedance spectra of the PSCs (fabricated with a semitransparent top electrode) are measured under illumination from the top and bottom sides, respectively, while maintaining the same device operation condition (e.g., same V oc , J sc ) in each measurement. Then, the recombination resistance of the device is extracted by fitting and comparing the Nyquist plots of the two measurements and identifying the dominant recombination sites inside the device.…”

Two Quasi-interfacial p-n Junctions Observed by a Dual-Irradiation System in Perovskite Solar Cells

“…Thus, the J sc values from both the FTO and ITO sides show a linear relationship (Fig. S4b and S5b) with the simulated light intensity, indicating the charge carriers recombination caused by defects is low in the device [32][33][34][35][36] .…”

“…To examine the photophysics of such a dual-irradiation PSC system, the time of ight (TOF) photoconductivity, small perturbation transient photovoltaic (TPV), nite-difference time-domain (FDTD) optical simulations were performed, collectively revealing that fast interfacial charge extraction and transportation occurring at the two quasi p-n interfaces are responsible for this PCE enhancement. Furthermore, the illumination-side-dependent impedance spectroscopy (ISD-IS) 32 was used to infer the dominant recombination pathway (e.g., interface or bulk) and validate the presence of two quasi-interfacial p-n junctions in the PSC. Our new PSC structure with a dual-irradiation con guration offers a new insight into perovskite photovoltaic physics and device integration, and this type of novel PSC dual-irradiation systems is potentially useful for many applications.…”