Insights into Recombination Processes from Light Intensity–Dependent Open‐Circuit Voltages and Ideality Factors in Planar Perovskite Solar Cells

Abstract

To analyze the dominant recombination, researchers often consider the diode ideality factor (nid), determined from the fitting of a semi‐log plot of light intensity–dependent open‐circuit voltage (Voc(lnI/I0)) to a linear dependence. This value is called “nid,Voc”. Theoretically, nid is the exponential dependence factor in the recombination rate function of the split of quasi‐Fermi levels. This nid is called “nid,C”. Herein, correlations between nid,Voc, nid,C, and the dominant recombination are reconsidered using a validated numerical drift–diffusion model and a diode current analysis in perovskite solar cell devices having accumulations of charged defects near the carrier transporting interfaces. It is found that the interplay between the recombination processes affects the linearity of the Voc(lnI/I0) plots. Devices having a single dominant recombination process exhibit Voc(lnI/I0) plots that appear to be linear, resulting in nid,Voc ≈ nid,C of the dominant recombination. Conversely, bends in the Voc(lnI/I0) curves indicate that different (multiple) recombination mechanisms dominate at different light intensities, so nid,Voc is an effective nid of the total diode current whose value is not consistent with any nid,C values. This work provides more understanding of nid and how to interpret a Voc(lnI/I0) curve more correctly for the insights into recombination mechanisms.

Light Intensity Analysis of Photovoltaic Parameters for Perovskite Solar Cells

“…Continuing to keep symmetrical interfacial defects, we characterize the changes of the V oc over the range of light intensity when both bulk and interface recombination is introduced into the PV system. The light intensity dependency of V oc and the ideality factor are intensively described in the literature, [50,[52][53][54] but here we split bulk and interface recombination and correlate our findings with the FF.…”

Unveiling the Influence of the Spectral Irradiance of Indoor Light‐Emitting Diodes on the Photovoltaics of a Methylammonium Lead Iodide‐Based Device

“…The nature of the illumination spectra (whether it is from an incandescent light, fluorescent light, or LED light source) will significantly affect the determination of device efficiency, which is done by simulating the current-voltage ( J-V ) plot by solving the Poisson drift-diffusion equation subject to appropriate continuity equations. [26,27] To understand how LED illumination influences the number of free carriers in a perovskite absorbing layer, we follow our previous work, [26] which used optical transfer matrix analysis [27] to calculate the free carrier generation rate (G(x)) from wavelengthdependent optical constants. For example, we used the carrier generation profiles of the MAPbI 3 perovskite that were based on the absorption of wavelengths between 300 and 800 nm, in which a previous drift-diffusion code and an LED spectral irradiance spectrum at 3 W m À2 was used as input data in an opensource transfer matrix model.…”

“…A further correlation of G(x) to a more accurate photocurrent density ( J ph ) in regard to the perovskite thickness can be obtained through the use of the following equation [26,28] J ph ¼ q…”

Universal Passivation Strategy for the Hole Transport Layer/Perovskite Interface via an Alkali Treatment for High‐Efficiency Perovskite Solar Cells

“…From a light intensity–dependent V oc measurement, one can distinguish between bimolecular and trap‐assisted recombinations. [ 44,45 ] The ideality factor ( n ) was determined from the slope of V oc versus the light intensity. If the value of n is close to unity, trap‐assisted carrier recombinations are considered to be largely absent.…”