Probing Perovskite Carrier Dynamics under Sunlight

Understanding the nature of photogenerated carriers and their subsequent dynamics in perovskites is important for the development of related materials and devices. Most ultrafast dynamic measurements on the perovskite materials were conducted under high carrier densities, which likely obscures the genuine dynamics at low carrier densities under solar illumination conditions. In this study, we presented a detailed experimental study of the carrier density-dependent dynamics in hybrid lead iodide perovskites using a highly sensitive transient absorption spectrometer. We found that the carrier lifetime was about a hundred nanosecond in the linear response range, representing sunlight excitation, which was much longer than under high carrier densities. We also elucidated that the fast carrier decay (<1 ps) and the medium decay processes (tens of ps) occurred via the defect state trapping, and we determined its effects on the utilization percentage of photogenerated carriers through quantitative analysis. Furthermore, we obtained the Shockley-Queisser limit that took into account the carrier trapping effect, which directly reflected the material performance.

Carrier dynamics in two-dimensional perovskites: Dion-Jacobson vs. Ruddlesden-Popper thin films

Quasi-two dimensional perovskites have emerged as candidates of high-performance materials for various optoelectronic applications due to the unique excitonic properties in their multilayer structures. Both Dion–Jacobson perovskites and Ruddlesden-Popper phases...

Atomistic Origin of Lattice Softness and Its Impact on Structural and Carrier Dynamics in Three Dimensional Perovskites

The soft lattices of lead-halide perovskites (LHPs) are responsible for their unique material properties, including polaron formation, defect tolerance, anharmonic vibration, and large electrostrictive response, which result in exotic carrier...

Effect of ligand groups on photoexcited charge carrier dynamics at the perovskite/TiO2 interface

First principles modeling of excited state dynamics of charge carriers at the interface between the perovskite and electron transport layer in perovskite solar cells identifies an effect of the interface morphology onto efficiency of charge transfer.

Polarization-Dependent Ultrafast Carrier Dynamics in GaAs with Anisotropic Response

The transient dynamics of anisotropic properties of GaAs is systematically studied by polarization-dependent ultrafast time-resolved transient absorption. Our findings revealed that the anisotropy of reflectivity was enhanced in both pump-induced and probe-induced processes, suggesting an extraordinary resonance absorption of photon-phonon coupling (PPC) with intrinsic anisotropic characteristic in carrier relaxation, regardless of the concrete crystallinity and orientation of GaAs sample. The results, delivering in-depth cognition about the polarization-dependent ultrafast carrier dynamics, also proved the paramount importance of interaction between polarized laser and semiconductor.

Charge carrier dynamics and photovoltaic properties of near-infrared absorbing squaraine incorporated solution-processed additive-free PTB7:PCBM based ternary solar cells

The introduction of a third component vehemently modifies the morphology and charge carrier dynamics in the blend of a donor-acceptor pair, thereby affecting the photovoltaic properties of organic solar cells (OSCs). Combining steady-state, impedance, and transient spectroscopic measurements, photovoltaic properties of 2,4-bis[4-(N,N-diisobutylamino)-2,6-dihydroxyphenyl] squaraine (DIB SQ) incorporated additive-free PTB7:PC70BM OSCs are assessed. As observed from steady-state measurements, concomitant enhancement in open-circuit voltage and short-circuit current has caused 33% enhancement in power conversion efficiency with good reliablity and reproducibility. On introducing 25 wt.% SQ to the OSCs, VOC has increased from 0.74 to 0.80 V while JSC has improved from 11.3 to 13.9 mAcm-2 with an increment in exciton dissociation probability rate from 81.5% to 94.9%. However, the fill factor values show inconsistent marginal variations with SQ addition. Equivalent circuit modeling of bias-voltage dependent impedance spectra along with transient photovoltage measurements reveal an improvement in effective charge carrier lifetime for the SQ incorporated OSCs, in comparison to the binary device. The addition of SQ also ensures better charge transport and extraction, as evidenced from photo-CELIV and transient photocurrent analysis. Atomic force microscopic (AFM) images confirm effective tuning of the morphology of the active layer when SQ is introduced into the binary blend, favoring efficient charge dissociation and transport. The possible operation mechanism of SQ incorporated ternary OSCs is proposed based on photoluminescence and AFM measurements. Moreover, the un-encapsulated OSC with 25 wt.% SQ has retained 91% of the initial PCE, while for the binary device, the PCE has declined to ~ 75% of the initial value after 200 hours of continous 1 sun illumination from a white LED in ambient atmosphere.