News
October 2024
Jasmeen finished her investigation on the oxidation of spin-coated lead tin perovskites. This demanding study requires real oxygen free handling at all times of the samples. After some real hard work by a number of students, technicians and we managed to perform a real nice study in which we quantitatively oxidise the perovskite! Our work highlights that even a short-term exposure to oxygen immediately affects the charge carrier dynamics of the perovskite, while structural perovskite degradation is only noticeable upon long-term exposure and accumulation of oxidation products.
Summer 2024
Jiashang finished her PhD with 2 impressive papers on the triple cation perovskites (CsMAFA). One paper published in AFM (https://doi.org/10.1002/adfm.202311727) focuses on the effect of temperature on the crystal phase as measured by XRD and TRMC. Most importantly, CsMAFA exhibits the lowest amount of microstrain in the β-phase at around 240 K, corresponding to the lowest density of traps, which translates into the longest charge carrier diffusion length for electrons and holes. The other paper published in ACS EL (https://doi.org/10.1021/acsenergylett.4c00250) deals with the quantification of the charge collection by the transport layers in double and for the first time also in triple layers. We show that by applying bias illumination charging of the TLs occurs which prevents additional charge extraction, demonstrating long-lived charge separation over the CsMAFA/TLs.
June 2023
In this paper we show how we use sMIM to measure the conductivity in semiconductor layers with a resuloution better than 100 nm. Using this electrodeless technique we see how in situ optically excited charges evenly distribute over MAPbI3 grains. In contrast we found inhomogeneous carrier distribution over grains in CsFAPbI3 with non-preferential orientation. For this paper our master students Verena and Jim have done most of the measurements and calculations!
March 2023
Windy excursion to Delft wind mill
September 2022
Valentina Caselli and other members of the OM group have succeeded in performing double pulse excitation TRMC experiments to study trapping and detrapping processes in semiconductor materials. In this paper published in Cell Reports: Physcial Sciences, we report that in the double metal perovskite, Cs2AgBiBr6 a higher photoconductance up to 30 micros after the first excitation can be observed. This is explained by the higher charge carrier yield, which is related to the population of trap states by the first pulse. Using additional photoluminescence and transient absorption measurements in collaboration with Eline Hutter from Utrecht university we show a very slow detrapping of these states extending over many microseconds.
July 2022
In this paper published in JPCL we finally succeeded in quantifying recombination losses in bare MAPbI3 and extraction into the TLs (C60 or Spiro-OMeTAD). This allows us to find the bottlenecks to increase the open-circuit voltage in perovskite-based solar cells.
May 2022
In this paper publsihed in ACS AEM we study together with the group of Annalisa Bruno from NTU, Singapore the structural and optoelectronic properties of co-evaporated MAPbI3 films varying in thickness (100, 400, and 750 nm). These layers show a gradient in composition leading to a gradient in the Fermi level giving rise to an internal electric field is formed. Side-selective time-resolved microwave photo conductivity measurements show an elongation of the charge carrier lifetimes which we explain by the fact that excess carriers separate under the influence of the electric field, preventing rapid decay in the thick films.
March 2022
Our new glovebox finally arrived!
March 2022 group activity in Delft
Both groups found the exit in time in the escape rooms!
February 2022
Hannes Hempel from Helmholtz-Zentrum Berlin, Germany has written together with many groups all over the world a best practice paper in Advanced Energy Materials focussing on perovskites using TRMC and OPTP. Identical samples have been send out and measured to cross check the acquisition and processing of the data. Furthermore an overview is provided how we can use these data for predicting solar cell performance.
December 2021
Jin has published a very nice, comprehensive overview entitled: "Progress and challenges on scaling up of perovskite solar cell technology" published in Sustainable Energy and Fuels
August 2021
We are happy to have contributed a little to this very interesting Advanced Functional Materials paper from Jia Li and Annalisa Bruno and coworkers from NTU, Singapore entitled: "Co-Evaporated MAPbI3 with Graded Fermi Levels Enables Highly Performing, Scalable, and Flexible p-i-n Perovskite Solar Cells".
May 2021
We are happy that we could contribute to a very interesting study published in Physical Science from Jinsong Huang and co-workers, entitled: "Perovskite solar cells with embedded homojunction via nonuniform metal ion doping". In particular, we provide some insight why time-resolved PL and photoconductivity measurements are so different.
March 2021
Jiashang Zhao has published her first, first-author paper entitled: "How Deep Hole Traps Affect the Charge Dynamics and Collection in Bare and Bilayers of Methylammonium Lead Bromide" in ACS AMI. She nicely shows how by subtle modifying the spin-coating conditions huge changes can be observed in the opto-electronics properties in thin layers of bromide perovskites.
January 2021
We are very happy that the new temperature microwave cells designed and created by Martien Vermeulen with DEMO have arrived. These truly unique cells are cooled by liquid nitrogen and the stainless steel parts act as thermal isolators. They are goldplated from the inside and outside to warrant a low surface resistivity and a high quality factor.
November 13, 2020
Together with Eline Hutter of UU and Bruno Ehrler of AMOLF Valentina has a new paper in ACS Energy Letters entitled "Charge Carrier Dynamics upon Sub-Bandgap Excitation in Methylammonium Lead Iodide Thin Films: Effects of Urbach Tail, Deep Defects and Two Photon Absorption". In this paper we try to further understand the opto-electronic properties of metal halide perovskites by illumination with sub band-gap light. For this study, the charge carrier dynamics in methylammonium lead iodide (MAPbI3) films were probed by time-resolved microwave conductivity measurements.
October, 2020
We are very happy that our scanning microwave module from Prime Nano has arrived and is installed by Marcel Bus on the Bruker AFM machine. This electrode-less technique enables local dielectric measurements with nanometer sized resolution. In this way variations in local electronic properties in our perovskite layers will be studied by Katerina. Here a test image of a mixed cation, mixed halide lead perovskite polycrystalline layer.
September 28, 2020
Sohan Phadke did his master project under supervision of Valentina on bimetal halide perovskites. He defended his thesis last month successfully and was awarded cum laude! Congratulations! He combined synthetic work with calculations under supervision of Grozema
July 14, 2020
Quantifying Charge‐Carrier Mobilities and Recombination Rates in Metal Halide Perovskites from Time‐Resolved Microwave Photoconductivity Measurements
We published this overview paper In the special issue of Advanced Energy Materials entitled: "Halide perovskites-Optoelectronic and structural characterisation methods". This paper describes in detail the TRMC setup and shows some of the highlights of Dengyang and Elines theses.
November 25, 2019
Together with Dr Claudine Katan and prof Jacky Even from Rennes, France we have described the double photon absorption in metal halide perovskite in a Nature Communication paper. In particular the agreement of our sub band-gap microwave measurements and the calculations from Rennes is astonishing!
April 10, 2019
Zimu Wei, master chemical engineering defended her thesis with almost the highest grade possible in the Dutch system: 9.5 congratulations!
March 18, 2019
Our nw paper on determining the fermi level splitting is out in ACS Energy Letters.
In this work we derive the Fermi-level splitting for various, non-contacted perovskites, using rate constants and mobilities obtained from time-resolved photoconductivity measurements. Comparison of those with experimental Voc values will help to select whether the perovskite layer or the used transport layers needs improvement to enhance the efficiency of corresponding devices. 
December 19, 2018
We escaped from the tower in 47 minutes!
September 7, 2018
Elines ACS Energy Letter, entitled "Thermally Activated Second-Order Recombination Hints toward Indirect Recombination in Fully Inorganic CsPbI3 Perovskites" is among the most read articles for the past month according the prof. Kamat!.
June 19, 2018
After defending her thesis work successfully Eline Hutter received her doctorate diploma with honours! Well done Dr Hutter! 
March 22, 2018
We're happy to announce that our paper to stabilize mixed halide perovskites using potassium can be found now in the latest issue of Nature! Of course special thanks to Mojtaba Abdi-Jalebi and Sam Stranks from Cambridge university for this great achievement. More information can also be found here.
February 27,28 2018
Lot's of talks from Delft at ABX3 in Rennes!
February 5, 2018
Davide's paper describing the charge dynamics in lead free perovskites is on line in JPPC. This work on silver bismuth bromide perovskites is a collaboration with Adam and Hema from the Karanudasa group Stanford, US and Maria from the Grozema group.
January 26, 2018
Our paper together with LMU, Munich and Uni Wurzburg in Adv. Energy Mat. is on line: Understanding the Role of Cesium and Rubidium Additives in Perovskite Solar Cells: Trap States, Charge Transport, and Recombination
Januari 24, 2018
Eline Hutter and Sudeep Maheshwari presented their work today at the FOM meeting in Veldhoven. Both gave excellent talks in a splendid and vivid perovskite session! Well done!
September 26, 2017
Today we had our yearly group activity together with the rest of the opto-electronic materials section. After a golf clinic and lunch in Leidschendam we went to The Hague to visit the Mauritshuis followed by a nice dinner. Everthing very well organized by our secretary, Wil Stolwijk.
September 15, 2017
Our paper by Roberto Brenes and Dengyang Guo is now in the first issue of Joule. We're also on the front cover! It has catched the attention of a number of popular scientific news papers. Check out these sites edited by Jeremy Deaton:
August 23, 2017
Dengyang Guo has published his first paper as first author on MAPbBr3 single crystals in J. Physical Chem Lett. A perfect example of combining TRMC and PL to reveal charge carrier dynamics in perovskites. This paper was a nice collaboration with the group of Jinsong Huang, US.
July 28, 2017
Eline Hutter and Rebecca Sutton from the Snaith group have succeeded in converting and keeping thin films of CsPbI3 in the black phase. Results can be found in this ACS Energy letters paper. Well done everybody!
June 19, 2017
MSc Eline Hutter received the prestigious Fulbright scholarship in Utrecht. This scholarship will allow her to spend 3 months in the US in autumn to carry out research at Stanford University under supervision of Dr. Hemamala Karunadasa. In Stanford Eline will work on the synthesis of lead free perovskite materials for photovoltaic applications. Congratulations with this impressive achievement!