Photo-Carrier Multi-Dynamical Imaging at the Nanometer Scale in Organic and Inorganic Solar Cells

Garrillo, Pablo A. Fernández; Borowik, Łukasz; Caffy, Florent; Demadrille, Renaud; Grévin, Benjamin

doi:10.1021/acsami.6b11423

Cited by 24 publications

(28 citation statements)

References 50 publications

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“…1 ), a case which resembles the effect of charge generation, separation, and recombination. Thus, the pulse shape with exponential rise and fall is closer to what is expected to be observed in an experiment [ 25 , 30 ]. Fig.…”

Section: Resultssupporting

confidence: 84%

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Artifacts in time-resolved Kelvin probe force microscopy

Sadewasser

Nicoara

Solares

2018

Beilstein J. Nanotechnol.

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Kelvin probe force microscopy (KPFM) has been used for the characterization of metals, insulators, and semiconducting materials on the nanometer scale. Especially in semiconductors, the charge dynamics are of high interest. Recently, several techniques for time-resolved measurements with time resolution down to picoseconds have been developed, many times using a modulated excitation signal, e.g., light modulation or bias modulation that induces changes in the charge carrier distribution. For fast modulation frequencies, the KPFM controller measures an average surface potential, which contains information about the involved charge carrier dynamics. Here, we show that such measurements are prone to artifacts due to frequency mixing, by performing numerical dynamics simulations of the cantilever oscillation in KPFM subjected to a bias-modulated signal. For square bias pulses, the resulting time-dependent electrostatic forces are very complex and result in intricate mixing of frequencies that may, in some cases, have a component at the detection frequency, leading to falsified KPFM measurements. Additionally, we performed fast Fourier transform (FFT) analyses that match the results of the numerical dynamics simulations. Small differences are observed that can be attributed to transients and higher-order Fourier components, as a consequence of the intricate nature of the cantilever driving forces. These results are corroborated by experimental measurements on a model system. In the experimental case, additional artifacts are observed due to constructive or destructive interference of the bias modulation with the cantilever oscillation. Also, in the case of light modulation, we demonstrate artifacts due to unwanted illumination of the photodetector of the beam deflection detection system. Finally, guidelines for avoiding such artifacts are given.

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Section: Resultssupporting

confidence: 84%

“…In typical experiments of time-resolved KPFM [ 22 , 24 – 25 27 – 28 30 ], spectra as a function of the modulation frequency are recorded. We simulated the spectral dependence of the CPD as a function of the period of the modulated bias.…”

Section: Resultsmentioning

confidence: 99%

Artifacts in time-resolved Kelvin probe force microscopy

Sadewasser

Nicoara

Solares

2018

Beilstein J. Nanotechnol.

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“…These transitional processes take about several seconds (calculated according to the probe scan rate) to build the dynamic equilibrium between E pd and E bi . We attribute this transitional process to coupled ionic transport under illumination, and need to be further investigated by the surface potential time response under frequency modulated illumination . We termed this dynamic equilibrium after the average CPD value is stable under illumination as Period C.…”

Section: Resultsmentioning

confidence: 99%

Carrier Transfer Behaviors at Perovskite/Contact Layer Heterojunctions in Perovskite Solar Cells

Wang

et al. 2018

Adv Materials Inter

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Hybrid halide perovskite based on CH3NH3PbI3 and related materials has emerged as the most exciting development in the next generation photovoltaic technologies. There is still requirement for an effective method to establish a relationship between the charge transfer behaviors and photovoltaic properties. This study presents Kelvin probe force microscopy and conductive atomic force microscopy measurements of versatile perovskite films that participate in the formation of different heterojunctions, exploring local current, contact potential difference (CPD), and charge activities at the nanoscale. By comparing the values of CPD and current of these perovskite films in dark and under illumination, the charge transfer behaviors are locally illustrated, suggesting that the perovskite roles in these heterojunctions are strictly dependent on the contact layers. Furthermore, the average difference (ΔV) of the CPD values obtained in dark and under illumination for each heterojunction can be set to analyze the efficacy of the perovskite/contact layer interfaces. The ΔV polarity is related to the type of charge carrier (hole or electron), while the ΔV magnitude is related to the number of charge carrier. These results emphasize the importance of understanding of these heterojunction systems that could guide the design and optimization of the photovoltaic configuration.

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“…By analyzing the dependency of the average potential with respect to the modulation frequency, it is possible to extract time constants characterizing the photopotential decay dynamics between the light pulses. More information about KPFM operations under frequency-modulated illumination (FMI-KPFM) can be found in our previous report [ 20 ].…”

Section: Methodsmentioning

confidence: 99%

Multimodal noncontact atomic force microscopy and Kelvin probe force microscopy investigations of organolead tribromide perovskite single crystals

Almadori¹,

Moerman²,

Martinez³

et al. 2018

Beilstein J. Nanotechnol.

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In this work, methylammonium lead tribromide (MAPbBr3) single crystals are studied by noncontact atomic force microscopy (nc-AFM) and Kelvin probe force microscopy (KPFM). We demonstrate that the surface photovoltage and crystal photostriction can be simultaneously investigated by implementing a specific protocol based on the acquisition of the tip height and surface potential during illumination sequences. The obtained data confirm the existence of lattice expansion under illumination in MAPbBr3 and that negative photocarriers accumulate near the crystal surface due to band bending effects. Time-dependent changes of the surface potential occurring under illumination on the scale of a few seconds reveal the existence of slow ion-migration mechanisms. Lastly, photopotential decay at the sub-millisecond time scale related to the photocarrier lifetime is quantified by performing KPFM measurements under frequency-modulated illumination. Our multimodal approach provides a unique way to investigate the interplay between the charges and ionic species, the photocarrier-lattice coupling and the photocarrier dynamics in hybrid perovskites.

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Photo-Carrier Multi-Dynamical Imaging at the Nanometer Scale in Organic and Inorganic Solar Cells

Cited by 24 publications

References 50 publications

Artifacts in time-resolved Kelvin probe force microscopy

Artifacts in time-resolved Kelvin probe force microscopy

Carrier Transfer Behaviors at Perovskite/Contact Layer Heterojunctions in Perovskite Solar Cells

Multimodal noncontact atomic force microscopy and Kelvin probe force microscopy investigations of organolead tribromide perovskite single crystals

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