Professor Tsai Chih-hao's research team at the University of Hong Kong published a research paper titled "Device deficiency and degradation diagnosis model of perovskite solar cells through hysteresis analysis" in the journal Nature Communications. Team member Wang Zishuai serves as the first author, and Tsai Chih-hao and Huang Zhixiang serve as corresponding authors.
Key Highlights: This paper proposes a method using a customized ion drift-diffusion simulator to comprehensively investigate the relationship between the current density-voltage (J-V) hysteresis characteristics of perovskite solar cells (PSCs) and key device issues. The paper also derives the root causes of device degradation, providing a new approach for addressing and optimizing the operational stability of PSCs.
Hysteresis is a unique and important characteristic of perovskite solar cells (PSCs) due to the slow dynamics of mobile ions within the perovskite film. This behavior results in undefined cell current density-voltage (J-V) curves, depending on the voltage sweep protocol. J-V characteristics provide rich information about device properties. For example, defects in the contact layer can be investigated by studying the severely S-shaped J-V curves. However, most measured J-V curves do not exhibit distinct features such as an S-shape, making them ineffective for directly diagnosing device performance.
Previous studies of the J-V characteristics of PSCs have identified factors contributing to solar cell efficiency losses and characterized radiative and nonradiative recombination, series and shunt resistance, and contact quality. However, these studies, while diagnosing bottlenecks in solar cells (including bulk/surface recombination losses, interface energy alignment, and carrier mobility), have overlooked the unique and important hysteresis caused by ion migration in PSCs. Interestingly, because device hysteresis is governed by the interplay between ion migration and various device defects, J-V hysteresis characteristics can reveal hidden information about the device (such as ion migration for electric field modulation, recombination, and transport). Therefore, simple analysis of hysteresis characteristics holds promise for rapidly uncovering device physics. Furthermore, in addition to identifying device defects, understanding the source of degradation is crucial for fabricating more stable devices.
In this study, researchers proposed and built a highly efficient, custom drift-diffusion simulator capable of comprehensively investigating the relationship between different J-V hysteresis characteristics and device defects, such as losses caused by defects on the perovskite surface and in the bulk, and low carrier mobility in the layer. Experimental results demonstrate that J-V hysteresis analysis can be used to diagnose device defects. For example, devices exhibiting specific hysteresis characteristics are diagnosed as suffering from extensive surface-recombination (SHR) recombination, potentially accompanied by low carrier mobility in the perovskite bulk region. These issues are attributed to film quality and bulk defects. Devices exhibiting Type D characteristics indicate extensive surface recombination at the interface, which can be eliminated through surface passivation due to surface defects. Devices exhibiting Type E characteristics suggest that the device issues reside in both the bulk and the interface. For Type F, it is suggested that the device issues may originate from bulk recombination and are associated with inefficient carrier extraction. Comparing hysteresis curves at the same voltage scan rate also allows for the assessment of the impact of bulk or surface recombination in the device.
Fig. 1 | Simulated hysteresis characteristics. a, b, c bulk recombination effect dependent hysteresis characteristics. d surface recombination dependent hysteresis characteristics. e, f synergetic effects induced hysteresis characteristics. “F” and “R” refer to forward and reverse voltage scans, respectively. The schematic diagram of simulated device configuration is inserted in (a).
Fig. 2 | Simulated hysteresis of the high-performance PSCs with different voltage scan rates and FR protocol. a device configuration diagram of simulated n-i-p PSC.
b scan rates dependent JV characteristics of PSC, where “Ref” refers to the reference device without mobile ion.
Fig. 3 | Simulated hysteresis originated from the dominated SRH recombination in perovskite bulk. a τSRH of 1 ns and (b) 10 ns. The simulated transient E-field in the middle of perovskite bulk vs applied voltage compared with the corresponding hysteresis curves of (c) 0.1 V/s and (d) 10 V/s scan in (a). “Ref” refers to the reference device without mobile ion. e, f the position-dependent potential and bulk recombination profiles under a bias of 0.8 V, respectively.
Fig. 4 | Simulated hysteresis originated from the dominated surface recombination. The interfaces recombination between perovskite and CTLs with (a) τsurf = 10 ns and (b)τsurf = 1 ns. The simulated transient E-field at perovskite/HTL interface vs applied voltage compared with the corresponding hysteresis curves of (c) 0.1 V/s and (d) 1 V/s in (a). “Ref” refers to the reference device without mobile ion.
Fig. 5 | Simulated hysteresis originated from low conductivity. a mobility of perovskite is μn(p) = 0.02 cm2 /Vs and (b) mobility of ETL is μn = 2 *10−5 cm2 /Vs.
Fig. 6 | Simulated hysteresis originated from surface and bulk recombination. a τSRH = 100 ns, τsurf = 10 ns and (b) τSRH = 10 ns, τsurf = 10 ns.
Fig. 7 | Comparison of the experimental and theoretical performances of the of PSCs with a large voltage loss. a experimental J–V hysteresis curves of the PSCs before and after the surface passivation treatment. b simulated J–V hysteresis curves of the PSCs with the same scan protocol as in experiments. The term “Control-F/R” denotes the control device under forward/reverse scan, respectively.
Fig. 8 | Comparison of the experimental and theoretical performances of PSCs suffering from degradation of perovskite bulk. a experimental J–V hysteresis curves of the PSCs before and after 300 h’ operation test. b simulated J–V hysteresis curves of the PSCs with the same scan protocol as in experiments.
本文来源：DOI: 10.1038/s41467-024-53162-z
https://doi.org/10.1038/s41467-024-53162-z