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1st January 1970 - Day 1 (Thursday)
General session G1
10.00 - 10.30 Presentation
10.30 - 11.00 Invited Mora-Seró, Iván

Applications of perovskite nanoparticles in optoelectronic devices

Iván Mora-Seró*

Universitat Jaume I, Av. de Vicent Sos Baynat, s/n, Castellón, 12071, ES

 Halide perovskite are receiving a huge attention in the recent few years. Undoubtedly this attention is mainly due to the outstanding power conversion efficiencies, surpassing 24%, reported for photovoltaic devices, fabricated with polycrystalline films from low cost techniques. The great success of halide perovskites boosted also the interest on the nanoparticles (NPs) of these materials. Perovskite NPs are also generating a huge interest as relative easy preparation methods yield a simple core structure, without need for passivating shells, reach photoluminescence quantum yield (PLQY) higher than 90%.This remarkable PLQY points to low non-radiative recombination and consequently shows excellent rationale for the development of solar cells and optoelectronic devices. In this talk I show the interest of perovskite NPs in the development of different optoelectronic systems and analyze the similarities and differences with standard bulk perovskite thin films. Interestingly the use of NPs can help to overcome some limitations of bulk perovskites stabilizing new interesting crystalline phases or avoiding mixed halide ion migration. In addition, the interaction of perovskites with other materials can provide useful synergies and their potentialities commented.


11.00 - 11.30 Invited Martínez Pastor, Juan P.

Exciton recombination dynamics in Metal Halide Perovskites: from bulk to nanocrystals

Juan P. Martínez Pastor*

Universidad de Valencia, Instituto de Ciencia de los Materiales, VALENCIA, 46071, ES

Metal halide perovskites (MHPs) have emerged as a very high promising materials for optoelectronics and photonics, mostly due to their large absorption coefficient and excellent quantum yield of emission at room temperature, among other electro-optical properties of MHPs. The absorption coefficient is dependent on the material electronic structure and hence mostly intrinsic, but other electro-optical parameters, as the emission quantum yield, will depend on radiative and non-radiative recombination channels for free (and bound) excitons and carriers. In this way, slow carrier recombination in MHPs is considered the origin of the observed large charge carrier diffusion length due to the existence of shallow non-quenching traps in these materials [1, 2]. In the talk a revision of recombination dynamics in MHPs will be presented, as the basis to understand their successful applications in photonics. In this sense, MHPs have been successfully integrated in optical waveguides where stimulated emission is observed with very low thresholds both on rigid [3-4] and flexible (in this case integrating a photodetector) [5] substrates. Finally, the optical properties and exciton recombination dynamics will be discussed in multi-quantum-well structures (or 2D/3D) perovskites and purely inorganic MHP (CsPbBr3 – CsPbI3) nanocrystals. 

REFERENCES

[1] Chirvony, V. S.; González-Carrero, S.; Suárez, I.; Galian, R. E.; Sessolo, M.; Bolink, H. J.; Martínez-Pastor, J. P.; Pérez-Prieto, J. Delayed luminescence in lead halide perovskite nanocrystals. J. Phys. Chem. C 2017, 121, 13381-13390.

[2] Chirvony, V. S.; Martínez-Pastor, J. P. Trap-limited dynamics of excited carriers and delayed luminescence in metal halide perovskites. J. Phys. Chem. Lett. 2018, accepted.

[3] I. Suárez, E. J. Juárez-Pérez, I. Mora-Seró, J. Bisquert and J. P. Martínez-Pastor, “Polymer/perovskite amplifying waveguides for active hybrid silicon photonics”,Advanced Materials 27,6157(2015).

[4] T. T. Ngo, I. Suarez, G. Antonicelli, D. Cortizo-Lacalle, J. P. Martinez-Pastor, A. Mateo-Alonso and I. Mora-Sero, “Enhancement of the Performance of Perovskite Solar Cells, LEDs and Light Amplifiers by Anti-Solvent Additive Deposition”, Advanced Materials 29, 1604056 (7 pp) (2017).

[5] I. Suarez, E. Hassanabadi, A. Maulu, N. Carlino, C. A. Maestri, M. Latifi, P. Bettotti, I. Mora-Sero and J. P. Martinez-Pastor, “Integrated Optical Amplifier-Photodetector on a Wearable Nanocellulose Substrate”, Advanced Optical Materials, 1800201 (8 pp)(2018).

 


11.30 - 11.45 Contr Macias, David

Theory study of PbS quantum dots embedded in Methyl-Ammonium perovskite matrix

David Macias*a, Iván Mora*b, Ignacio Climente*c

Universitat Jaume I, Calle Fola 2 1, Castellón de la Plana, 12004, CO

“Theory of PbS Quantum Dots embedded in Methyl-Ammonium Perovskite Matrix”

There is current interest in enhancing the energy window of efficient light harvesting of lead halide perovskites by introducing sub-band gap quantum dots.[1] PbS are natural candidates to this end, as they have a similar crystal structure to that of the surrounding perovskite material. Core/shell PbS/CdS quantum dots have been tested so far.[2,3], but a direct use of PbS quantum dots on the methyl ammoninum perovskite matrix is of interest for ehnhaced transfer of the sub-band absorbed carriers. To shed light on the dot-matrix interaction, we carry out simulations of excitonic states of 2-band k·p Hamiltonian for rocksalt[4] in 3D heterostructures, obtained via a self-consistent inclusion of Coulomb interaction. This allows us to survey how optical absorption is influenced by a large number of potentially relevant physical factors, including quantum confinement, dielectric confinement, external electric fields and electron-hole interaction.

REFERENCES

[1] Ning Z. et al. Nature 2015, 523, 324. [2] Ngo T.T. et al., Nanoscale, 2016, 8, 14379-14383. [3] Sanchez R. et al., Science Adv. 2016, 2, 1501104. [4] Inuk Kang and Frank W. Wise, J. Opt. Soc. Am. B 1997 ,14, 1632.


11.45 - 12.00 Contr Suárez, Isaac

Towards Metal Halide Perovskite Nonlinear Photonics

Isaac Suárez*a, Juan Martínez-Pastorb, Albert Ferrandob, Iván Morac, Marta Vallésc, Andrés Gualdrónc

a, Universidad Rey Juan Carlos, C/Camino del Molino s/n , Fuenlabrada, 28943, ES
b, Universidad de Valencai, C/Catedrático Jose Beltrán 2, Paterna, es
c, Universidad Jaime I, Avenida de Vicent Sos Baynat, s/n, 12071 Castellón de la Plana, Castellón, es

The possibility of controlling light using the nonlinear optical properties of photonic devices opens new points of view in information and communications technology applications. We firstly analyze the potential role of metal halide perovskites (MHPs) as nonlinear photonic materials. The characterization of their nonlinear parameters becomes necessary to pave the road on nonlinear MHP-based devices, which is up to now at its very beginning. In this work we will present our results on β (nonlinear absorption) and n2 (nonlinear refraction) obtained by transmission and Z-scan technique on CH3NH3PbX3 polycrystalline films and colloidal nanoparticles of CsPbX3 for X = I3, Br3 and Br1.5I1.5 under pulsed nanosecond excitation regime. These materials exhibit a bright generation of photoluminescence under the illumination of pulsed infrared light, and hence demonstrate an excellent efficiency of multiphoton absorption. In this way, the parameter β results to be very high, β=1500 cm/GW, as obtained from transmission experiments. In the case of n2, as deduced from Z-scan experiments, we deduce values up to 3.5 cm2/GW. These results indicate the suitability of MHPs materials to construct active nonlinear photonic devices.


12.00 - 12.15 Contr Aranda Alonso, Clara

High Power Conversion Efficiency Perovskite Solar Cells Fabricated under Moisture Conditions and Reduction of Photovoltage loses by Interfacial Engineering

Clara Aranda Alonso*

Universitat Jaume I, Avda. Sos Baynat s/n, Castelló, 12006, ES

Perovskite solar cells (PSCs) have acquired a tremendous impact in the photovoltaic field due to their impressive properties, acquiring power conversion efficiencies (PCE) upon 24% combined with low fabrication costs. In fact, photocurrents in PSCs are almost at their practical limits, just remaining, in terms of photovoltaic parameters, the suppression of photovoltage loses, dominated by recombination dynamics. However, these achievements are useless in terms of large-scale fabrication if the stability issues of perovskite material against moisture exposure are not completely solved. In this work, a universal method of PSCs fabrication under real environmental conditions is presented succeeding photocurrents of 23 mA/cm2 for a simple MAPbI3-based device. As a second achievement, a sustainable reduction of photovoltage loses in bromide-based perovskite material is reached by interfacial engineering process, obtaining an impressive open-circuit potential of 1.58V with an enhanced photoluminescence response.

 

"High Power Conversion Efficiency Perovskite Solar Cells Fabricated under Moisture Conditions and Reduction of Photovoltage loses by Interfacial Engineerin"


12.15 - 12.30 Contr Pashaei Adl, Hamid

Temperature-Sensitive Enhancement of Spontaneous Emission of Cs Pb I3 Perovskite Nano-Crystals by Hyperbolic Metamaterials

Hamid Pashaei Adla, Isaac Suareza, b, Setatira Gorjia, Vladimir Chirvonya, Andrés Gualdrón-Reyesd, Ivan Mora Serod, Carlos Zapata Rodríguez*c, Juan Martínez Pastor*a

a, University of Valencia, Instituto de Ciencia de Materiales (ICMUV), Universidad de Valencia, C/ Catedrático José Beltrán, 2, E-46980 Paterna, Spain, Valencia, 46980, ES
b, School of Telecommunications Engineering, Electronics Area, Camino del Molino s/n E 28942 Fuenlabrada, Spain, ES
c, Departament d’Òptica i Optometria i Ciències de la Visió, Universitat de València, , Dr Moliner, 50, 46100 Burjassot, Valencia, Spain, ES
d, Institute of Advanced Materials (INAM), Universitat Jaume I, Castelló 12006, Spain, ES

 

 

     In this work we present a temperature dependent investigation of the spontaneous emission (SE) rate of CsPbI3 perovskite nanocrystals enhanced by means of Hyperbolic Metamaterials (HMMs) substrates. On the one hand, the development of nanofabrication techniques enabled the experimental demonstration of different types of optical metamaterials, proposed to manifest properties of light-matter interaction unattainable with regular media [1]. Among the varieties of metamaterials proposed and fabricated so far, HMMs have rapidly gained a key role in nanophotonics due to their peculiar ability to manipulate the near-field of a quantum emitter (QE) [2]. When thin metallic/dielectric layers are periodically stacked, the electromagnetic fields bounded to the individual plasmonic interfaces couple, giving rise to a collective response. One of the results of such response is the SE manipulation of the QE [3, 4]. Accordingly, in this work the HMM structures have been fabricated by alternatively depositing thin metal (Ag) and dielectric (LiF) layers with the thickness of 25 nm and 45 nm respectively by means of thermal evaporation under high vacuum. On the other hand, it is well-known the outstanding optical properties of perovskites that lead to highly efficient solar cells and photonic devices [5]. For this reason, we have chosen CsPbI3 perovskite nanocrystals as QEs. One of the parameters affecting the above given applications is the exciton lifetime of these nanocrystals. However, the exciton lifetime can be affected by dark states associated to certain surface traps in perovskite materials/nanomaterials, which acts as a reservoir of trapped carriers [6]. For this reason, the manipulation of the excitonic SE in CsPbI3 nanocrystals by HMM substrates will be better observed under low temperatures where exciton recombination is predominantly radiative. We have determined that the fabricated HMM, exhibiting a dielectric constant anisotropy of ε||≈-7.4+i0.6 (parallel with interfaces) and ε≈+3.2+i0.01 (perpendicular to the interfaces) at λ=785 nm, induces a reduction of the exciton lifetime of around 0.8 ns, which arises from the optical coupling of the CsPbI3 emitters to the modes of the HMM.

 

References:

 

[1]  Y. Liu, X. Zhang, “Metamaterials: a new frontier of science and technology”, Chem. Soc. Rev. 40, 2011, 2494–2507.

[2]  S. Maier, “Plasmonics: Fundamentals and Applications: Fundamentals and Applications”, Springer, New York, 2007.

[3]  K. C. Shena, C. Hsieha, Y. J. Chenga, D. P. Tsaia, “Giant enhancement of emission efficiency and light directivity by using hyperbolic metacavity on deep-ultraviolet AlGaN emitter”, Nano Energy, 45, 2018, 353–358.

[4]   L. N. Tripathi, O. Iff, S. Betzold, L. Dusanowski, M. Emmerling, K. Moon, Y.J . Lee, S. H. Kwon, S. Höfling, and C. Schneider, “Spontaneous Emission Enhancement in Strain-Induced WSe2 Monolayer-Based Quantum Light Sources on Metallic Surfaces”, ACS Photonics, 5, 2018, 1919−1926.

[5]  J. B. Edmandsa, G. E. Eperon, R. D. Johnson, H. J. Snaith, P. G. Radaelli, “Non-ferroelectric nature of the conductance hysteresis in CH3NH3PbI3 perovskite-based photovoltaic devices”, App. Phys. Lett. 106, 2015, 173502.

[6]  V. S. Chirvony, S. González-Carrero, I. Suarez, R. E. Galian, M. Sessolo, H. J. Bolink, J. P. Martinez-Pastor, J. Pérez-Prieto, “Delayed Luminescence in Lead Halide Perovskite Nanocrystals”, J. Phys. Chem. C, 24, 2017, 13381-13390.

 


12.30 - 12.45 Contr López-Fraguas, Eduardo

Can perovskites go commercial? My research on tin-halide perovskites.

Eduardo López-Fraguas*

Carlos III University of Madrid, Avda. Universidad 30, Leganés, 28911, ES

Nowadays, lead-halide perovskites have achieved great efficiencies over 23% on the last reports. With only a few years of development, the most used MAPbIperovskite have reached the level of the classical silicon solar cells. But the main problem in these perovskites is that they suffer a degradation process which generates lead, leading onto high toxicity problems. Latest researches have tried to get rid of the lead, replacing it with another similar element (e.g. Sn, Ge…). One of the most promising materials for this substitution is tin, which has a similar size as lead (ionic radii), so it does not disturb the original perovskite structure. Typical perovskite combinations have been studied, like MASnI3, FASnIand CsSnI3. The perovskites with the organic cation have demonstrated higher efficiencies that the inorganic ones, but have poorer stability, due to the organic cation itself. That is why all-inorganic lead-free perovskite seems to be a good candidate to work with. The CsSnIperovskite has a narrower bandgap than his lead homologues, thus it has better absorbance. The main problem of this perovskite is that Sn2+ is not a stable element in standard atmosphere conditions, because it is very sensitive to oxygen and moisture. This oxidation process generates Sn4+, which creates defects in the perovskite, generating a huge p-type self-doping, giving the material an almost metallic behavior. This phenomenon is the main responsible of the poor response of the devices, that shows a short-circuit behavior. But, we can see this from another perspective, making a perovskite based on the Sn4+ oxidation state, more stable in air. Cs2SnIis generated with the goal of being a good light absorber, stable in the standard atmosphere and non-toxic. This perovskite is the same as CsSnI3, but with the half of the Sn atoms missed, forming [SnI6]2- octahedral. In this talk I will explain the fabrication process of CsSnIand how it oxidizes to its precursors (CsI and SnI2), rebuilding itself after several hours in the more stable perovskite Cs2SnI6. I will also explain all the optical characterization of the material that I did, demonstrating that this perovskite is a better absorber of light than the typical MAPbI3. However, more research must be done in order to obtain a good material without defects to improve its electric response because, until now, the best report of a solar cell built with this perovskite is 0.96% efficiency, which nevertheless is a better value than the first value achieved by a solar cell of CsSnI(0.9%).


12.45 - 13.00 Contr Redondo Obispo, Carlos Daniel

Ion migration influence into Photo-Stability Enhancement in Bismuth Doped NH3CH3PbI3 Perovskites

Carlos Daniel Redondo Obispo*a, Javier Bartoloméb, c, Esteban Climent Pascuala, c, Alicia de Andrésb, Carmen Coyaa

a, Escuela Técnica Superior de Ingeniería de Telecomunicación (ETSIT), Universidad Rey Juan Carlos, C/Tulipan s/n, depar II, 061, 28933 Móstoles , ES
b, Instituto de Ciencia de Materiales de Madrid, Consejo Superior de Investigaciones Científicas, C/ Sor Juana Inés de la Cruz 3, 28049 Madrid, ES
c, Departamento de Física de Materiales, Universidad Complutense de Madrid, Plaza Ciencias 1, 28040 Madrid, ES
d, Escuela Técnica Superior de Ingeniería Industrial, Universidad Politécnica de Madrid, C/ José Gutiérrez Abascal 2, 28006 Madrid, ES

The extraordinary efficiency values reached with MAPbI3 (MA: CH3-NH3+) based photovoltaic cells has recently boosted the efforts in the search of new hybrid perovskite alternatives for photovoltaic energy production. However there still are unsolved questions and drawbacks, as ion-migration phenomenon which stands as a potential threat against stability [1]. In this work, we have synthesised MAPb1-1.5xBix€Π0.5xI3, where €Π€ stands for cation vacancy with x=0.08, 0.13 and 0.18. We analyse in detail novel structural and photo physical effects that are consistent with Bi3+ migration leading to a final material with a huge photo-stability [2]. The tetragonal perovskite structure remains stable at least up to 7 at. % Bi incorporation with a reduction of the lattice parameters that is used to estimate the Bi3+ fraction at Pb2+ sites. At low intensity irradiation, visible emission of doped samples is quenched as previously reported, but surprisingly, at high power irradiation, visible emission emerges and these Bi doped MAPbI3 films are extraordinarily resistant to light modifications, being stable for extremely high power densities > 100 W/cm2 compared to undoped samples (0.1 W/cm2). The observed trends can be explained using a model based on the migration of Bi3+ out of the perovskite lattice upon irradiation and its effect on the MAPbI3 cell volume and bandgap energy. Based on micro photoluminescence, Raman and EDS maps analysis, we propose that the mechanism origin of this increased stability is related to Bi migration that favours different reactions leading to the formation first of BiI3 and then to the stable bismuth oxyiodide compound (BiOI), at the surface of the grains, which competes with the usual decomposition mechanisms into PbI2 and PbOx in undoped MAPbI3. These results can be a valuable resource for future studies of photovoltaic device behaviour.

[1] A. K. Jena et al. Halide Perovskite Photovoltaics: Background, Status, and Future Prospects. 2019, Chem.Rev. DOI: 10.1021/acs.chemrev.8b00539.

[2] J. Bartolomé, et al. Huge Photo-Stability Enhancement in Bismuth Doped Methylammonium Lead Iodide Hybrid Perovskites by Light Induced Transformation. Chem.Matter. 2019 (Accepted).


13.00 - 13.30 Invited Bisquert, Juan

Time Scales of Ionic and Electronic Phenomena in Perovskite Solar Cells

Juan Bisquert*

Universitat Jaume I, Avda Sos Baynat , Castello , 120006, ES

We suggest a classification of the time scales for ionic/electronic phenomena in the perovskite solar cells, based on the results of analysis of kinetic phenomena using frequency modulated techniques and time transient techniques. First with impedance spectroscopy we provide an interpretation of capacitances as a function of frequency both in dark and under light, and we discuss the meaning of resistances and how they are primarily related to the operation of contacts in many cases. The capacitance reveals a very large charge accumulation at the electron contact, which has a great impact in the cell measurements, both in photovoltage decays, recombination, and hysteresis. We also show the identification of the impedance of ionic diffusion by measuring single crystal samples. Working in samples with lateral contacts, we can identify the effect of ionic drift on changes of photoluminescence, by the creation of recombination centers in defects of the structure. We also address new methods of characterization of the optical response by means of light modulated spectroscopy. The combination of IMPS and Impedance Spectroscopy is able to provide a detailed picture that explains low frequency characteristics, influencing the fill factor of the solar cell.


13:30 Lunch
15.30 - 16.00 Invited Garcia-Belmonte, Germà

Insights to perovskite solar cell mechanism by impedance spectroscopy

Germà Garcia-Belmonte*

Universitat Jaume I, Av. V. Sos Baynat s/n, Castelló, 12071, ES

Hybrid lead halide perovskite-based solar cells have rapidly reached very large solar to electricity power conversion efficiencies. The most extensively studied has been the CH3NH3PbI3 (MAPbI3) perovskite (or its analogous but using chlorine precursor: CH3NH3PbI3-xClx) as absorber materials, in combination with electron (TiO2) and hole (spiro-OMeTAD) selective contacts. The current density–voltage curves of perovskite solar cells (PSCs) have been found to present a hysteresis-like distortion when the measurement is done by sweeping the applied voltage at different scan conditions. Hysteresis has raised many concerns about the feasibility and long term stability of this kind of photovoltaic technology. Recent experimental work shows a connection between capacitive current and hysteresis behavior in hybrid lead halide perovskites.1 The microscopic phenomena responsible for capacitive currents is the ionic electrode polarization, similar to double layer capacitive effects, while the perovskite absorber layer behaves as a mixed conductor able to interact with the contacting transport layers. Here we show how contact phenomena distort the current-voltage curve by using different cell structures. We differentiate the different types of interactions of the standard electrode contacts. They display qualitatively diverse sources of reactivity at the interface between MAPbI3 and the transporting layers which give rise to distinct current-voltage curves. At TiO2 contact, reversible capacitive currents are observed. On the other hand irreversible ionic reaction occurs between mobile ions in MAPbI3 and spiro-OMeTAD organic hole extracting layer. Only the latter irreversible behavior may cause significant long term aging by reduction of spiro-OMeTAD conductivity, and it is therefore a key point for engineering of the solar cell towards long time robust operation.2 Further fundamental experiments have revealed the electrical structure of the interfacial double-layer formed by mobile ions at non-interacting Au contacts providing an overall picture of ionic interfacial effects. In relation to the commonly reported hysteretic response there is however a lack of distinction among different hysteretic phenomena which is necessary to unravel its underlying physical and chemical mechanisms. We distinguish here between capacitive and non-capacitive currents giving rise to specific hysteretic responses in the J-V curves of PSCs. It is reported that capacitive current causing hysteresis dominate in regular structures with TiO2 as bottom electron selective layer. This is mainly caused by the charge, both ionic and electronic, accumulation ability of the TiO2/perovskite interface, but has no influence on the steady-state operation. Noncapacitive hysteresis is observable at slow enough scan rates in all kind of architectures. Inverted structures, including organic compounds as bottom hole selective layers and fullerene materials as top contact, exhibit larger noncapacitive distortions because of the inherent reactivity of contact materials and absorber perovskites.3 

1.  Almora, O.; Zarazua, I.; Mas-Marza, E.; Mora-Sero, I.; Bisquert, J.; Garcia-Belmonte, G., Capacitive Dark Currents, Hysteresis, and Electrode Polarization in Lead Halide Perovskite Solar Cells. J. Phys. Chem. Lett. 2015, 6, 1645−1652.

2.  Carrillo, J.; Guerrero, G.; Rahimnejad, S.; Almora, O.; Zarazua, I.; Mas-Marza, E.; Bisquert, J.; Garcia-Belmonte, G.,Ionic Reactivity at Contacts and Aging of Methylammonium Lead Triiodide Perovskite Solar Cells. Adv. Energy Mater. 2016, 6, 1502246. 

3. Almora, O.; Aranda, C.; Zarazua, I.; Guerrero, G.; Garcia-Belmonte, G., Noncapacitive Hysteresis in Perovskite Solar Cells at Room Temperature. ACS Energy Lett. 2016, 1, 209−215


16.00 - 16.30 Invited Anta, Juan A

Impedance analysis of perovskite solar cells: some recent findings

Juan A Anta*

Universidad Pablo de Olavide, Crta. de Utrera km. 1, Sevilla, 41013, ES

Metal halide perovskites are mixed electronic-ionic semiconductors with an extraordinary rich optoelectronic behavior and the capability to function very efficiently as active layers in solar cells, with a record efficiency surpassing 23% nowadays. In this work, we carry out an impedance spectroscopy analysis of two perovskite solar cells with quite distinct optical and electrical characteristics, i.e. MAPbI3 and CsPbBr3-based devices. The main aim of the analysis is to establish how, regardless the inherent complexity of the impedance spectrum due to ionic effects, information like ideality factors, recombination losses and the collection efficiency can be qualitative and quantitatively assessed from impedance experiments at operating conditions. We have also investigated  perovskite-based solar cells with various n-type metal-oxide electron selective contacts of different chemical nature and crystal structure. Our main finding is that the open-circuit photovoltage remains essentially independent of the nature of the contact for highly selective electron contacts, a fact that we attribute to a recombination rate that is mainly governed by the bulk of the MHPs. In contrast, replacement of the “standard” TiO2 contact by alternative contacts leads to lower short-circuit photocurrents and more pronounced hysteresis, related to enhanced surface recombination at less effective electron selective contacts 


16.30 - 17.00 Invited Gallardo, Juan Jesús

Synthesis and characterization of the structural, optical and photoluminescence properties of CsxMA(1-x)PbI3 perovskite quantum dots

Juan Jesús Gallardoa, Javier Navas*a, Eduardo Blancob, Antonio Sánchez Coronillac, José Carlos Piñerod

a, Dpto. Química Física (Universidad de Cádiz), Facultad de Ciencias. Campus Universitario Río San Pedro, Puerto Real, 11510, ES
b, Dpto. Física de la Materia Condensada (Universidad de Cádiz), Facultad de Ciencias. Campus Universitario Río San Pedro, Puerto Real, 11510, ES
c, Dpto. Química Física (Universidad de Sevilla), Facultad de Farmacia. Campus Reina Mercedes, Sevilla, 41012, ES
d, Dpto. Didáctica (Área Matemáticas) (Universidad de Cádiz), Facultad de Ciencias de la Educación. Campus Rio San Pedro, Puerto Real, 11510, ES

Hybrid organic-inorganic perovskites, with an ABX3 structure, have been widely investigated in recent years due to their role as light absorbers in photovoltaic devices resulting in highly efficient solar cells, and as emitters for a variety of applications in a quantum dots way. In this sense, the ability to control the emission properties of perovskite quantum dots (PQDs) nowadays is of great interest. In this work, CsxMA(1-x)PbI3 (x = 0; 0.1; 0.2; 0.3; 0.5) PQDs were synthesized and characterized to determine their structural, optical and electronic properties, through the application of techniques such as TEM, EDX, XPS, XRD, UV-Vis spectroscopy, PL measurements and periodic-DFT calculations. PQDs of a maximum size of 5 nm were obtained, and a transition from tetragonal structure to orthorhombic was found when the amount of Cs as doping agent increased in the samples. This transition affects the optical properties, verified by the UV-Vis spectra and the PL measurements. A shift in the emission peak in the range from 670 nm to 740 nm of the electromagnetic spectrum was found for the PQDs samples with x >= 0.2, and changes in the quantum yield (QY) and recombination lifetime were observed when Cs was incorporated into the samples. The shift in the emission is observed to be due to the displacement of the valence band edge, but this is not because of an electronic effect resulting from the incorporation of Cs, obtained from the PDOS analyses performed by periodic-DFT calculations. It is likely due to the change in the crystal phase from tetragonal to orthorhombic phase of the samples when the amount of Cs increased. Therefore, in this way the emission properties of the PQDs synthesized can be regulated according to the amount of Cs incorporated in their crystal lattice.


17.00 - 17.15 Contr Ravishankar, Sandheep

Intensity Modulated Photocurrent Spectroscopy (IMPS) and its application to Perovskite Solar Cells

Sandheep Ravishankar*

Universitat Jaume I, Vicent sos Baynat, Castellon, 12006, IN

Small perturbation techniques are a useful tool to understand processes occurring on different timescales in a solar cell. However, traditional methods of Impedance Spectroscopy (IS) have raised more questions than answers regarding the operation of the perovskite solar cell (PSC). In order to complement and strengthen the information obtained from IS, IMPS measurements were carried out on stable and efficient Iodide and Bromide-based PSCs. The slow timescales of response of the order of milliseconds-seconds observed from several experiments such as IS and OCV decay were also inevitably reflected in IMPS measurements. Furthermore, the IMPS Q-plane response showed a singular reduction in the external quantum efficiency (EQE) of the PSC at very low frequencies. By development of definitions EQE and a suitable EC, this was related to the large LF capacitance and the separation of the photovoltage internally. The timescale of this detrimental response means that standard methods of measurement of the EQE, that usually involve the input photon flux modulated by a chopper that is operating between 10-200 Hz, can be highly erroneous in the case of PSCs and require rigorous reporting protocols. In addition, an intermediate frequency response is observed in IMPS that is not observed in IS due to the nature of the time constants formed in either technique, whose corresponding elements have a significant effect on the fill factor of the PSC.


17.15 - 17.30 Contr Arenas, Juan

CsPbX3 nanocrystal thin films as a gain material for photonic devices

Juan Arenas*a, Andrés F. Gualdrón-Reyesb, Vladimir S. Chirvonya, Iván Mora-Serób, Isaac Suáreza, Juan Martínez-Pastora

a, Instituto de Ciencia de Materiales (ICMUV), Carrer del Catedrátic José Beltrán Martinez, 2, 46980 Paterna, València, Valencia, 46980, ES
b, Institute of Advanced Materials (INAM), Universitat Jaume I, Castelló, València, 12006, ES
c, School of Telecommunications Engineering, Universidad Rey Juan Carlos, Camino del Molino, Fuenlabrada, 28942, ES

During the last years, Metal Halide Perovskites (MHPs) have attracted special attention as solar cell materials or optical sources. In spite of the fact that most of the works have been focussed on CH3NH3PbX3 (X=Cl,Br,I) polycrystalline thin films, MHP can be also synthesized as colloidal nanocrystals (NCs). In particular, caesium lead halide perovskite CsPbX3 NCs revealed extraordinary properties for active photonics derived from their extremely high quantum yield of emission (>90 %) and narrow linewidths (100 meV). In this work, the optical gain properties of CsPbX3 NCs with three different bandgaps (X3=Br3, X3=Br1.5I1.5, X3= I3) are thoroughly studied. For this purpose, the NCs are homogenously deposited on thin films by a simple dip coating method that allows a homogeneous distribution of the nanoparticles on the substrate. Then, photoluminescence of the films is studied as a function of the temperature in order to understand the non-radiative channels limiting the optical gain and how to prevent them in future optoelectronic devices.  As a preliminary results, we observed the Amplified Spontaneous Emission (ASE) with thresholds below 10 μJ/cm2 when the films are optically pumped at criogenic temperatures. Future directions include the demonstration of ASE at room temperature, the minimization of the threshold and the integration in photonic devices that exploit the excellent gain properties.


17.30 - 17.45 Contr Rubino, Andrea

Temperature-dependent photoluminescence of MAPbI3 nanocrystals

Andrea Rubinoa, Mauricio Calvo*a, Hernan Miguez*a

CSIC-US, Calle Americo Vespucio 49, Sevilla, 41092, ES

Despite the incredible success of perovskites in the field of research on opotelectronic devices in particular for photovoltaics and for the generation of light, thanks to the results already competitive obtained in a really short period of time, the study of these materials has not yet completed the identikit of the all properties and features. Among these, and in particular in the case of perovskite nanocrystals, the dependence of the bandgap of these semiconductors with temperature variations, is still scarcely debated, although already in the bulk material the behavior differs from the more general one found in most inorganic semiconductors [1,2]. And considering the possible modifications on the electronic structure of perovskites reducing dimensionality (towards quantum confinement regimes), and the consequences for example on the interactions with photogenerated species in a device, the profile deducible from this type of analysis could be central in optimization of materials. Through the method for the synthesis of perovskite nanocrystals already illustrated in some previous works [3], in this study we were able to analyze the behavior at low temperatures of nanocrystals encapsulated in a porous matrix based on silicon oxide and therefore avoiding added interferences, such as those of organic ligands or solvents or even electronic interactions with the matrix. We focused the work on methylammonium lead iodide and could obtain different information about the dependence of the gap on temperature and therefore on the thermal expansion and the contribution of the electron-phonon coupling together with the binding energies of the exciton of the nanocrystals. We can also obtain some information on the phase transitions. The results obtained so far seem to indicate an important change of trend with respect to the bulk material, which could suggest new strategies for improving the performances of these materials. 

[1]Electron–phonon coupling in hybrid lead halide perovskites Nature Communication 2015, 7, 11755. A.D. Wright et al.

[2]On the role of the electron-phonon interaction in the temperature dependence of the gap of lead halide perovskites arXiv:1903.10204 A. Francisco-López et al.

[3]Highly Efficient and Environmentally Stable Flexible Color Converters Based on Confined CH3NH3PbBr3 Nanocrystals, ACS Appl. Mater. Interfaces 2018,  10, 44, 38334-38340 A.Rubino et al.


17.45 - 18.00 Contr Calvo, Mauricio

Optical properties and devices with templated perovskite nanocrystals

Mauricio Calvo*a, Andrea Rubinoa, Hernán Mígueza

Instituto de Ciencia de Materiales de Sevilla, Americo Vespucio 49, Sevilla, 41092, ES

In this talk, I will describe a recently proposed method that leads to ABX3 perovskite nanocrystals based on the use of mesoporous materials as hosts of perovskite liquid precursors. These porous matrices permit the synthesis of perovskite nanocrystals through the strict control of the porous network. The ability to manage the microstructure of the pore array (geometry, pore size distribution) is traduced in a powerful tool to control/manipulate the structural and optical properties of ABX3 semiconductors synthesized within. The different methods based on one or two steps combined with porous matrices based on electrochemical etched materials, mesoporous metal oxides or templated polymers will be described in this talk. In particular, we are interested in the optical properties of the nanocrystals synthesized in the voids of the porous structures since free-ligand ABX3particles with sizes in the sub-5nm range can be obtained only by this synthetic approach. We also present the impact that this new type of method has in the field of different optoelectronic devices (light emitting devices, color converter layers and solar cells). Finally, I will present the approach developed by our group that allows us to prepare high quantum yield films with optical quality and nanocrystal based solar cells.


20:30 Dinner