Abstract
AbstractThe measurement of the ideality factor (nid) is a popular tool to infer the dominant recombination type in perovskite solar cells (PSC). However, the true meaning of its values is often misinterpreted in complex multilayered devices such as PSC. In this work, the effects of bulk and interface recombination on the nid are investigated experimentally and theoretically. By coupling intensity‐dependent quasi‐Fermi level splitting measurements with drift diffusion simulations of complete devices and partial cell stacks, it is shown that interfacial recombination leads to a lower nid compared to Shockley–Read–Hall (SRH) recombination in the bulk. As such, the strongest recombination channel determines the nid of the complete cell. An analytical approach is used to rationalize that nid values between 1 and 2 can originate exclusively from a single recombination process. By expanding the study over a wide range of the interfacial energy offsets and interfacial recombination velocities, it is shown that an ideality factor of nearly 1 is usually indicative of strong first‐order non‐radiative interface recombination and that it correlates with a lower device performance. It is only when interface recombination is largely suppressed and bulk SRH recombination dominates that a small nid is again desirable.
Highlights
Halide perovskite solar cells (PSC) have the potential to trigger a revolution in the photovoltaic sector due to their lowcost production and outstanding efficiention on the nid are investigated experimentally and theoretically
Our combined experimental/simulation study focusses on p-i-n type “triple cation” perovskite solar cells, where the ≈450 nm thick perovskite absorber is sandwitched between a ≈10 nm thick hole-transporting layer (HTL) polymer and 30 nm thick electron-transporting layer (ETL).[32]
We demonstrated the application of intensity dependent quasi-Fermi level splitting (QFLS) measurements on perovskite/transport layer junctions to gain a comprehensive understanding of the processes determining the ideality factor in perovskite solar cells
Summary
Halide perovskite solar cells (PSC) have the potential to trigger a revolution in the photovoltaic sector due to their lowcost production and outstanding efficiention on the nid are investigated experimentally and theoretically. We found the ideality factor of devices using poly[bis(4-phenyl) (2,4,6-trimethylphenyl)amine] (PTAA) as hole-transporting layer (HTL) to be around 1.3, which we could consistently attribute to trap-assisted recombination regardless of involving radiative second-order recombination Another process affecting the ideality factor is the recombination at the metal contacts, which may lead to a saturation of the VOC despite increasing the carrier density in the bulk, resulting in nid approaching a value of 1 (or even decreasing below unity) at high intensities (typically above 1 sun). Based on an analytical model, we explain how Shockley–Read–Hall (SRH) recombination at the perovskite/TL interface accounts for the rather low nid of all devices in this study In this picture, the ideality factor of the cell depends essentially on the asymmetry of the electron and hole quasi-Fermi levels at the dominant recombination site.
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