Intrinsic Photophysics Research Articles

Doping of Colloidal Nanocrystals for Optimizing Interfacial Charge Transfer: A Double-Edged Sword.

Doping of colloidal nanocrystals offers versatile ways to improve their optoelectronic properties, with potential applications in photocatalysis and photovoltaics. However, the precise role of dopants on the interfacial charge transfer properties of nanocrystals remains poorly understood. Here, we use a Cu-doped InP@ZnSe quantum dot as a model system to investigate the dopant effects on both the intrinsic photophysics and their interfacial charge transfer by combining time-resolved transient absorption and photoluminescent spectroscopic methods. Our results revealed that the Cu dopant can cause the generation of the self-trapped exciton, which prolongs the exciton lifetime from 48.3 ± 1.7 to 369.0 ± 4.3 ns, facilitating efficient charge separation to slow electron and hole acceptors. However, hole localization into the Cu site alters their energetic levels, slowing hole transfer and accelerating charge recombination loss. This double-edged sword role of dopants in charge transfer properties is important in the future design of nanocrystals for their optoelectronic and photocatalytic applications.

Absorption and fluorescence spectroscopy of cold proflavine ions isolated in the gas phase.

Proflavine, a fluorescent cationic dye with strong absorption in the visible, has been proposed as a potential contributor to diffuse interstellar bands (DIBs). To investigate this hypothesis, it is essential to examine the spectra of cold and isolated ions for comparison. Here, we report absorption spectra of proflavine ions, trapped in a liquid-nitrogen-cooled ion trap filled with helium-buffer gas, as well as fluorescence spectra to provide further information on the intrinsic photophysics. We find absorption- and fluorescence-band maxima at 434.2 ± 0.1 and 434.7 ± 0.3nm, corresponding to a Stokes shift of maximum 48cm-1, which indicates minor differences between ground-state and excited-state geometries. Based on time-dependent density functional theory, we assign the emitting state to S2 as its geometry closely resembles that of S0, whereas the S1 geometry differs from that of S0. As a result, simulated spectra involving S1 exhibit long Franck-Condon progressions, absent in the experimental spectra. The latter displays well-resolved vibrational features, assigned to transitions involving in-plane vibrational modes where the vibrational quantum number changes by one. Dominant transitions are associated with vibrations localized on the NH2 moieties. Experiments repeated at room temperature yield broader spectra with maxima at 435.5 ± 1nm (absorption) and 438.0 ± 1nm (fluorescence). We again conclude that prevalent fluorescence arises from S2, i.e., anti-Kasha behavior, in agreement with previous work. Excited-state lifetimes are 5 ± 1ns, independent of temperature. Importantly, we exclude the possibility that a narrow DIB at 436.4nm originates from cold proflavine cations as the band is redshifted compared to our absorption spectra.

Unveiling the Intrinsic Photophysics in Quasi-Two-Dimensional Perovskites.

The two-dimensional (2D) perovskites have drawn intensive attention due to their unique stability and outstanding optoelectronic properties. However, the debate surrounding the spatial phase distribution and band alignment among different 2D phases in the quasi-2D perovskite has created complexities in understanding the carrier dynamics, hindering material and device development. In this study, we employed highly sensitive transient absorption spectroscopy to investigate the carrier dynamics of (BA)2(MA)n-1PbnI3n+1 quasi-2D Ruddlesden-Popper perovskite thin films, nominally prepared as n = 4. We observed the carrier-density-dependent electron and hole transfer dynamics between the 2D and three-dimensional (3D) phases. Under a low carrier density within the linear response range, we successfully resolved three ultrafast processes of both electron and hole transfers, spanning from hundreds of femtoseconds to several picoseconds, tens to hundreds of picoseconds, and hundreds of picoseconds to several nanoseconds, which can be attributed to lateral-epitaxial, partial-epitaxial, and disordered-interface heterostructures between 2D and 3D phases. By considering the interplay among the phase structure, band alignment, and carrier dynamics, we have proposed material synthesis strategies aimed at enhancing the carrier transport. Our results not only provide deep insights into an accurate intrinsic photophysics of quasi-2D perovskites but also inspire advancements in the practical application of these materials.

Ultrafast transient absorption spectroscopy of 14 and 2.1 nm CsPbBr3 nanoparticles: Free carrier vs exciton

CsPbBr3 nanoparticles with averaged size of 14 and 2.1 nm (named as 14 and 2 nmNP, respectively) are synthesized capping with the ligand of dodecylbenzene sulfonic acid (DBSA). Using ultrafast transient absorption spectroscopy, free carriers in 14 nmNP characterize with the slow thermalization (∼0.76 ps) and long carrier cooling time (∼1 ns), which could be due to the phonon bottleneck effect. On the other hand, excitons are major photoexcitations in 2 nmNP, presenting with fast thermalization (<100 fs) and short cooling time (∼50 ps); this effective energy dissipation in 2 nmNPs can be ascribed to the involvement of phonons in DBSA ligands. In both 14 and 2 nmNP, we find that the photoexcitation accumulation leads to an increase in the bandgap that can be understood by the Burstein–Moss band filling effect. These results provide insights into the intrinsic photophysics of CsPbBr3 perovskite nanocrystals with different confinement effects, supplying direct implications for optoelectronic applications.

Stimulating Phonon Bottleneck Effect in Organic Semiconductors by Charge-Transfer-Mediated J-Aggregation.

Hot carriers rapidly lose kinetic energies on a subpicosecond time scale, posing significant limitations on semiconductors' photon-conversion efficiencies. To slow the hot carrier cooling, the phonon bottleneck effect is constructed prevalently in quantum-confined structures with discrete energy levels. However, the maximum energy separation (ΔEES) between the energy levels is in a range of several hundred meV, leading to unsatisfactory cooling time. To address this, we design a novel organic semiconductor capable of forming intermolecular charge transfer (CT) in J-aggregates, where the lowest singlet excited state (S1) splits into two states due to the significant interplay between the Coulomb interaction and intermolecular CT coupling. The ΔEES between the two states can be adjusted up to 1.02 eV, and an extremely slow carrier cooling process of ∼72.3 ps was observed by femtosecond transient absorption spectroscopy. Moreover, the phonon bottleneck effect was identified in organic materials for the first time, and CT-mediated J-aggregation with short-range interactions was found to be the key to achieving large ΔEES. The significantly prolonged carrier cooling time, compared to <100 fs in the isolated molecule (10-6 M), highlights the potential of organic molecules with diversified aggregation structures in achieving long-lived hot carriers. These findings provide valuable insights into the intrinsic photophysics of electron-phonon scattering in organic semiconductors.

Cross Relaxation Enables Spatiotemporal Color-Switchable Upconversion in a Single Sandwich Nanoparticle for Information Security.

Smart control of ionic interaction dynamics offers new possibilities for tuning and editing luminescence properties of lanthanide-based materials. However, it remains a daunting challenge to achieve the dynamic control of cross relaxation mediated photon upconversion, and in particular the involved intrinsic photophysics is still unclear. Herein, this work reports a conceptual model to realize the color-switchable upconversion of Tm3+ through spatiotemporal control of cross relaxation in the design of NaYF4:Gd@NaYbF4:Tm@NaYF4 sandwich nanostructure. It shows that cross relaxation plays a key role in modulating upconversion dynamics and tuning emission colors of Tm3+. Interestingly, it is found that there is a short temporal delay for the occurrence of cross relaxation in contrast to the spontaneous emission as a result of the slight energy mismatch between relevant energy levels. This further enables a fine emission color tuning upon non-steady state excitation. Moreover, a characteristic quenching time is proposed to describe the temporal evolution of cross relaxation quantitatively. These findings present a deep insight into the physics of ionic interactions in heavy doping systems, and also show great promise in frontier applications including information security, anti-counterfeiting and nanophotonics.

Cryogenic Ion Fluorescence Spectroscopy: FRET in Rhodamine Homodimers and Heterodimers.

The internal electronic communication between two or more light-absorbers is fundamental for energy-transport processes, a field of large current interest. Here we have studied the intrinsic photophysics of homo- and heterodimers of rhodamine cations where just two methylene units bridge the dyes. Gas-phase experiments were done on frozen molecular ions at cryogenic temperatures using the newly built LUNA2 mass spectroscopy setup in Aarhus. Both absorption (from fluorescence excitation) and dispersed-fluorescence spectra were measured. In the gas phase, there is no dielectric screening from solvent molecules, and the effect of charges on transition energies is maximum. Indeed, bands are redshifted compared to those of monomer dyes due to the electric field that each dye senses from the other in a dimer. Importantly, also, as two chemically identical dyes in a homodimer do not experience the same field along the long axis, each dye has separate absorption. At low temperatures, it is therefore possible to selectively excite one dye. We find that fluorescence is dominantly from the dye with the lowest transition energy no matter which dye is photoexcited. Hence our work unequivocally demonstrates Förster Resonance Energy Transfer even in homodimers where one dye acts as donor and the other as acceptor.

Thermalization and relaxation mediated by phonon management in tin-lead perovskites

Understanding and control of ultrafast non-equilibrium processes in semiconductors is key to making use of the full photon energy before relaxation, leading to new ways to break efficiency limits for solar energy conversion. In this work, we demonstrate the observation and modulation of slow relaxation in uniformly mixed tin-lead perovskites (MASnxPb1-xI3 and CsSnxPb1-xI3 nanocrystals). Transient absorption measurements reveal that slow cooling mediated by a hot phonon bottleneck effect appears at carrier densities above ~1018 cm−3 for tin-lead alloy nanocrystals, and tin addition is found to give rise to suppressed cooling. Within the alloy nanoparticles, the combination of a newly introduced high-energy band, screened Fröhlich interaction, suppressed Klemens decay and reduced thermal conductivity (acoustic phonon transport) with increased tin content contributes to the slowed relaxation. For inorganic nanocrystals where defect states couple strongly with carriers, sodium doping has been confirmed to benefit in maintaining hot carriers by decoupling them from deep defects, leading to a decreased energy-loss rate during thermalization and an enhanced hot phonon bottleneck effect. The slow cooling we observe uncovers the intrinsic photophysics of perovskite nanocrystals, with implications for photovoltaic applications where suppressed cooling could lead to hot-carrier solar cells.

Cryogenic Absorption and Emission Spectroscopy of the Oxyluciferin Anion In Vacuo.

Bioluminescence from fireflies, click beetles, and railroad worms ranges in color from green-yellow to orange to red. The keto form of oxyluciferin is considered a key emitter species in the proposed mechanisms to account for color variation. To establish the intrinsic photophysics in the absence of a microenvironment, we present experimental and theoretical gas-phase absorption and emission spectra of the 5,5-dimethyloxyluciferin anion (keto form) at room and cryogenic temperatures as well as lifetime measurements based on fluorescence. The theoretical model includes all 75 vibrational modes. The spectral impact of the large number of excited states at elevated temperatures is captured by an effective state distribution. At low temperature, spectral congestion is greatly reduced, and the observed well-resolved vibrational features are assigned to multiple Franck-Condon progressions involving different vibrational modes. An in-plane ∼60 cm-1 scissoring mode is found to be involved in the dominant progressions.

Probing the Genuine Carrier Dynamics of Semiconducting Perovskites under Sunlight.

Understanding the nature of photogenerated carriers and their subsequent dynamics in semiconducting perovskites is important for the development of solar cell materials and devices. However, most ultrafast dynamic measurements on perovskite materials were conducted under high carrier densities, which likely obscures the genuine dynamics under low carrier densities in solar illumination conditions. In this study, we presented a detailed experimental study of the carrier density-dependent dynamics in hybrid lead iodide perovskites from femtosecond to microsecond using a highly sensitive transient absorption (TA) spectrometer. From the dynamic curves with low carrier density in the linear response range, we observed two fast trapping processes that occurred in less than 1 ps and tens of picoseconds, attributed to the shallow traps, and two slow decays with lifetimes of hundreds of nanoseconds and longer than 1 μs, related to the trap-assisted recombination and trapping at deep traps. Further TA measurements clearly show that PbCl2 passivation can effectively reduce both shallow and deep trap densities. These results provide insights into the intrinsic photophysics of semiconducting perovskites with direct implications for photovoltaic and optoelectronic applications under sunlight.

A roadmap to decipher ultrafast photophysics in two-dimensional nanomaterials.

Atomically thin two-dimensional (2D) semiconductors are extensively investigated for optoelectronic applications that require strong light-matter interactions. In view of such applications, it is essential to understand how (photo)excitation alters the non-linear optical response of these materials under high carrier density conditions. Broadband transient absorption (TA) spectroscopy is by now a widely used tool to study the semiconductor physics in such highly excited systems. However, the complex interplay between different many-body interactions in 2D materials produces highly congested spectral information and an ensuing non-trivial non-linear photo-response, thereby masking the desired intrinsic photophysics. Herein, we outline a concise roadmap for analyzing such congested datasets based on examples of TA analysis of various 2D materials. In particular, we emphasize the synergy between an initial qualitative understanding of the transient photo-response based on line shapes and their derivatives and a consequent quantitative spectral deconvolution backed by such insights.

The impact of the chalcogen-substitution element and initial spectroscopic state on excited-state relaxation pathways in nucleobase photosensitizers: a combination of static and dynamic studies.

The substitution of oxygen with chalcogen in carbonyl group(s) of canonical nucleobases gives an impressive triplet generation, enabling their promising applications in medicine and other emerging techniques. The excited-state relaxation S2(ππ*) → S1(nπ*) → T1(ππ*) has been considered the preferred path for triplet generation in these nucleobase derivatives. Here, we demonstrate enhanced quantum efficiency of direct intersystem crossing from S2 to triplet manifold upon substitution with heavier chalcogen elements. The excited-state relaxation dynamics of sulfur/selenium substituted guanines in a vacuum is investigated using a combination of static quantum chemical calculations and on-the-fly excited-state molecular dynamics simulations. We find that in sulfur-substitution the S2 state predominantly decays to the S1 state, while upon selenium-substitution the S2 state deactivation leads to simultaneous population of the S1 and T2,3 states in the same time scale and multi-state quasi-degeneracy region S2/S1/T2,3. Interestingly, the ultrafast deactivation of the spectroscopic S3 state of both studied molecules to the S1 state occurs through a successive S3 → S2 → S1 path involving a multi-state quasi-degeneracy S3/S2/S1. The populated S1 and T2 states will cross the lowest triplet state, and the S1 → T intersystem crossing happens in a multi-state quasi-degeneracy region S1/T2,3/T1 and is accelerated by selenium-substitution. The present study reveals the influence of both the chalcogen substitution element and initial spectroscopic state on the excited-state relaxation mechanism of nucleobase photosensitizers and also highlights the important role of multi-state quasi-degeneracy in mediating the complex relaxation process. These theoretical results provide additional insights into the intrinsic photophysics of nucleobase-based photosensitizers and are helpful for designing novel photo-sensitizers for real applications.

Cryogenic Fluorescence Spectroscopy of Ionic Fluorones in Gaseous and Condensed Phases: New Light on Their Intrinsic Photophysics.

Fluorescence spectroscopy of gas-phase ions generated through electrospray ionization is an emerging technique able to probe intrinsic molecular photophysics directly without perturbations from solvent interactions. While there is ample scope for the ongoing development of gas-phase fluorescence techniques, the recent expansion into low-temperature operating conditions accesses a wealth of data on intrinsic fluorophore photophysics, offering enhanced spectral resolution compared with room-temperature measurements, without matrix effects hindering the excited-state dynamics. This perspective reviews current progress on understanding the photophysics of anionic fluorone dyes, which exhibit an unusually large Stokes shift in the gas phase, and discusses how comparison of gas- and condensed-phase fluorescence spectra can fingerprint structural dynamics. The capacity for temperature-dependent measurements of both fluorescence emission and excitation spectra helps establish the foundation for the use of fluorone dyes as fluorescent tags in macromolecular structure determination. We suggest ideas for technique development.

Approaching the intrinsic exciton physics limit in two-dimensional semiconductor diodes.

Two-dimensional (2D) semiconductors have attracted intense interest for their unique photophysical properties, including large exciton binding energies and strong gate tunability, which arise from their reduced dimensionality1-5. Despite considerable efforts, a disconnect persists between the fundamental photophysics in pristine 2D semiconductors and the practical device performances, which are often plagued by many extrinsic factors, including chemical disorder at the semiconductor-contact interface. Here, by using van der Waals contacts with minimal interfacial disorder, we suppress contact-induced Shockley-Read-Hall recombination and realize nearly intrinsic photophysics-dictated device performance in 2D semiconductor diodes. Using an electrostatic field in a split-gate geometry to independently modulate electron and hole doping in tungsten diselenide diodes, we discover an unusual peak in the short-circuit photocurrent at low charge densities. Time-resolved photoluminescence reveals a substantial decrease of the exciton lifetime from around 800 picoseconds in the charge-neutral regime to around 50 picoseconds at high doping densities owing to increased exciton-charge Auger recombination. Taken together, we show that an exciton-diffusion-limited model well explains the charge-density-dependent short-circuit photocurrent, a result further confirmed by scanning photocurrent microscopy. We thus demonstrate the fundamental role of exciton diffusion and two-body exciton-charge Auger recombination in 2D devices and highlight that the intrinsic photophysics of 2D semiconductors can be used to create more efficient optoelectronic devices.

Barrier-free reverse-intersystem crossing in organic molecules by strong light-matter coupling

Strong light-matter coupling provides the means to challenge the traditional rules of chemistry. In particular, an energy inversion of singlet and triplet excited states would be fundamentally remarkable since it would violate the classical Hund’s rule. An organic chromophore possessing a lower singlet excited state can effectively harvest the dark triplet states, thus enabling 100% internal quantum efficiency in electrically pumped light-emitting diodes and lasers. Here we demonstrate unambiguously an inversion of singlet and triplet excited states of a prototype molecule by strong coupling to an optical cavity. The inversion not only implies that the polaritonic state lies at a lower energy, but also a direct energy pathway between the triplet and polaritonic states is opened. The intrinsic photophysics of reversed-intersystem crossing are thereby completely overturned from an endothermic process to an exothermic one. By doing so, we show that it is possible to break the limit of Hund’s rule and manipulate the energy flow in molecular systems by strong light-matter coupling. Our results will directly promote the development of organic light-emitting diodes based on reversed-intersystem crossing. Moreover, we anticipate that it provides the pathway to the creation of electrically pumped polaritonic lasers in organic systems.

The nonlinear optical transition bleaching in tellurene

To date, outstanding linear and nonlinear optical properties of tellurene, caused by multiple two-dimensional (2D) phases and optical anisotropy, have attracted considerable interest for potential nanophotonics applications. In this work, the ultrafast nonlinear optical (NLO) properties of α-tellurene have been studied via Z-scan and pump-probe techniques at a broadband spectral region. Typical saturable absorption and band filling effects are observed in tellurene due to the Pauli exclusion principle. Analysis using density functional theory (DFT) computation shows the enhancements in NLO response within the ultraviolet-visible absorption spectral region are owing to the increased optical intraband transition in tellurene. Moreover, the effects of varying the photon energy of the probe pulse were explored. Our results indicated that probe pulses with higher photon energies can make smaller differential transmission signal, this effect is found to be negatively correlated with calculated joint density of states (JDOS). These results offer insights into the intrinsic photophysics of 2D tellurene, driving its applications in photonic and optoelectronic fields.

Intrinsic Exciton Photophysics of PbS Quantum Dots Revealed by Low-Temperature Single Nanocrystal Spectroscopy.

With a tunable size-dependent photoluminescence (PL) over a wide infrared wavelength range, lead chalcogenide quantum dots (QDs) have attracted significant scientific and technological interest. Nevertheless, the investigation of intrinsic exciton photophysics at the single-QD level has remained a challenge. Herein, we present a comprehensive study of PL properties for the individual core/shell PbS/CdS QDs emissive near 1.0 eV. In contrast to the sub-meV spectral line widths observed for II/VI QDs, PbS/CdS QDs are predicted to possess broad homogeneous line widths. Performing spectroscopy at cryogenic (4 K) temperatures, we provide direct evidence confirming theoretical predictions, showing that intrinsic line widths for PbS/CdS QDs are in the range of 8-25 meV, with an average of 16.4 meV. In addition, low-temperature, single-QD spectroscopy reveals a broad low-energy side emission attributable to optical as well as localized acoustic phonon-assisted transitions. By tracking single QDs from 4 to 250 K, we were able to probe temperature-dependent evolutions of emission energy, line width, and line shape. Finally, polarization-resolved PL imaging showed that PbS/CdS QDs are characterized by a 3D emission dipole, in contrast with the 2D dipole observed for CdSe QDs.

Frontispiece: Intrinsic Photophysics of Light‐harvesting Charge‐tagged Chlorophyll a and b Pigments

Frontispiece: Intrinsic Photophysics of Light‐harvesting Charge‐tagged Chlorophyll <i>a</i> and <i>b</i> Pigments

Intrinsic Photophysics of Light-harvesting Charge-tagged Chlorophyll a and b Pigments.

Chlorophylls a and b (Chla/b) are responsible for light-harvesting by photosynthetic proteins in plants. They display broad absorption in the visible region with multiple bands, due to the asymmetry of the macrocycle and strong vibronic coupling. Their photophysics relies on the microenvironment, with regard to transition energies as well as quenching of triplet states. Here, we firmly establish the splitting of the Q and Soret bands into x- and y- polarized bands for the isolated molecules in vacuo, and resolve vibronic features. Storage-ring experiments reveal that dissociation of photoexcited charge-tagged complexes occurs over several milliseconds, but with two different time constants. A fast decay is ascribed to dissociation after internal conversion and a slow decay to the population of a triplet state that acts as a bottleneck. Support for the latter is provided by pump-probe experiments, where a second laser pulse probes the long-lived triplet state.

Photoinduced charge carrier dynamics and spectral band filling in organometal halide perovskites

In recent years, the solution-processed organic-inorganic perovskite solar cells have attracted considerable attention because of their advantages of high energy conversion efficiency, low cost, and easily processing. Organometallic halide perovskite solar cells have gradually demonstrated particular superior properties in energy field due to their excellent photoelectric properties. This has been triggered by the unprecedented increase in its overall power conversion efficiency reaching 23% in just a few years, and it is becoming a direct competitor against the existing leading technology silicon. In this paper, 5-AVA-doped organometal halide perovskite films, (5-AVA)&lt;sub&gt;0.05&lt;/sub&gt;(MA)&lt;sub&gt;0.95&lt;/sub&gt;PbI&lt;sub&gt;3&lt;/sub&gt; and (5-AVA)&lt;sub&gt;0.05&lt;/sub&gt;(MA)&lt;sub&gt;0.95&lt;/sub&gt;PbI&lt;sub&gt;3&lt;/sub&gt;/Spiro-OMeTAD, are prepared by the two-step method. The generation and recombination mechanism of charge carriers in two kinds of film samples are discussed in detail. The bivalent band structure of perovskite film material CH&lt;sub&gt;3&lt;/sub&gt;NH&lt;sub&gt;3&lt;/sub&gt;PbI&lt;sub&gt;3&lt;/sub&gt; is determined by ultraviolet-visible absorption spectra of perovskite film (5-AVA)&lt;sub&gt;0.05&lt;/sub&gt;(MA)&lt;sub&gt;0.95&lt;/sub&gt;PbI&lt;sub&gt;3&lt;/sub&gt; and (5-AVA)&lt;sub&gt;0.05&lt;/sub&gt;(MA)&lt;sub&gt;0.95&lt;/sub&gt;PbI&lt;sub&gt;3&lt;/sub&gt;/Spiro-OMeTAD. We investigate the photocarrier dynamics and band filling effects in these two organometal halide perovskite films by using femtosecond transient absorption spectroscopy. For (5-AVA)&lt;sub&gt;0.05&lt;/sub&gt;(MA)&lt;sub&gt;0.95&lt;/sub&gt;PbI&lt;sub&gt;3&lt;/sub&gt;, the photoinduced bleach recovery at 760 nm reveals that band-edge recombination follows second-order kinetics, indicating that the dominant relaxation pathway is via the recombination of free electrons and holes. With regard to the perovskite film (5-AVA)&lt;sub&gt;0.05&lt;/sub&gt;(MA)&lt;sub&gt;0.95&lt;/sub&gt;PbI&lt;sub&gt;3&lt;/sub&gt; and (5-AVA)&lt;sub&gt;0.05&lt;/sub&gt;(MA)&lt;sub&gt;0.95&lt;/sub&gt;PbI&lt;sub&gt;3&lt;/sub&gt;/Spiro-OMeTAD, the signal is photoinduced absorption from 550 nm to 700 nm. As the delay time increases, the electrons and holes are recombined, which results in a red shift of absorption spectrum in (5-AVA)&lt;sub&gt;0.05&lt;/sub&gt;(MA)&lt;sub&gt;0.95&lt;/sub&gt;PbI&lt;sub&gt;3&lt;/sub&gt;. This can be referred to as Moss-Burstein band filling model. In contrast, the electrons and holes of (5-AVA)&lt;sub&gt;0.05&lt;/sub&gt;(MA)&lt;sub&gt;0.95&lt;/sub&gt;PbI&lt;sub&gt;3&lt;/sub&gt;/Spiro-OMeTAD perovskite film sample are separated after photoexcitation. The holes rapidly transfer to the hole transport layer of Spiro-OMeTAD. It will lead to an increase in sample absorbance and a rapid recovery of bleaching signals. Consequently, electron-hole recombination is no longer a dominant pathway to the relaxation of photocarriers and the band filling effect is not significant in the composite film. Our findings provide a valuable insight into the understanding of the charge carrier dynamics and spectral band filling in mixed perovskites. These results conduce to the understanding of the intrinsic photo-physics of semiconducting organometal halide perovskites with direct implications for photovoltaic and optoelectronic applications, and provide a reference for the future research of perovskite solar cells.