Understanding and Optimizing the operational stability of perovskite solar cells.

Professor Choy, Wallace Chik Ho   (Principal Investigator (PI))

Professor NAZEERUDDIN Mohammad Khaja   (Co-Investigator)

Professor Yin Wanjian   (Co-Investigator)

36

2022-01-01

838393

Understanding and Optimizing the operational stability of perovskite solar cells.

device optimization, drift-diffusion model, perovskite solar cells, stability prediction, trap evolution

Photonics

Engineering (E)

17200021

General Research Fund (GRF)

2021

On-going

1 Establishing the trap evolution and DTDD coupled model for the study of PSC degradation. We propose to establish an experimentally verified spatial and temporal trap evolution model coupled with DTDD model to address the degradation of PSCs beyond the limitation of typical solar cell (SC) models. As the interaction between the mobile ions/atoms and the trap state evolution has not been fully elucidated, we will study the trap effects on the diffusion of mobile ions/atoms in the whole device, which can be from the diffused particles in a PSC, as well as the decomposition and halide/cation segregation of a perovskite (all of which are widely considered as the dominant photo- and thermal- induced degradations). We will then introduce time- and space- dependent trap states and the corresponding trap-assisted recombination into DTDD model, and comprehensively study the effects of carriers (mobile ion, electron, hole) and trap states on the degradation of PSCs. The model will then be experimentally verified. Consequently, the coupled model will provide the fundamental and insightful device physics on the trap evolution and trap-assisted recombination loss in PSC degradation. 2 Diagnosing the device flaws in PSCs. Under continuous operation, the PSC deterioration is dominantly caused by the device flaws, including surface recombination at two interfaces of perovskites, bulk recombination of perovskite and low conductivity of PSC layers. Meanwhile, the interaction between the mobile ion migration induced electric field and the device flaws will result in various features found in J-V hysteresis. We therefore introduce the J-V hysteresis with rich information on PSC electrical properties as an indicator for the device flaws. By re-visiting and understanding the different general J-V hysteresis features, we can qualitatively investigate each of the device flaws by theoretical study through the coupled model, and by experimental study through designing and characterizing specific PSCs. With these comprehensive studies, we will not only consolidate the physical understanding of the device flaws but also validate the coupled model study on the J-V hysteresis as an effective and quick diagnosis to identify device flaws of PSCs. 3 . Identifying the origins of PSC operational degradation. Since identifying the origins of PSC degradation and efficiency losses during the device operation is very desirable for optimizing PSC performances, we will introduce the diagnostic method in Objective 2 for in-situ real-time study of the origins of PSC degradation during the long-term stability test which will shorten the time and cost of device optimization. Importantly, through optical correction of the coupled model using detailed balance theory, we will qualitatively and quantitatively evaluate the classified efficiency losses by the weighted contribution from each loss term, including the bulk recombination loss in perovskite, surface recombination loss at each interface of perovskite, optical loss, and loss from the low conductivity in the different layers. Meanwhile, we will investigate the electroabsorption spectroscopy of cross sections of PSCs at different degradation stages with the coupled model study to determine the degradation components/locations. Overall, the studies will offer the in-situ and effective diagnosis on the operational stability of PSCs, and allow as to determine and understand the degradation origins, qualitative and quantitative efficiency losses, and degraded locations. 4 Optimization of the operational stability of PSCs. Based on the coupled model offering comprehensive PSCs degradation physics, we will experimentally and theoretically study various CTL materials, to realize highly performed and stable PSCs made from various perovskites.