Mihail Popa - Academia.edu (original) (raw)
Papers by Mihail Popa
Spectroscopic technique is very useful for characterising semiconducting materials. We demonstrat... more Spectroscopic technique is very useful for characterising semiconducting materials. We demonstrate here a new method for determination the energy band gap of thin fims from reflectance data.
The reflection and transmission spectra (in the range from 300nm to 1400nm) were recorded using a... more The reflection and transmission spectra (in the range from 300nm to 1400nm) were recorded using a PMQ – II (Carl Zeiss, Jena) spectrophotometer. The absorption coefficient, was determined from transmission spectra. The values of optical band gap, Eg, have been determined by extrapolating the linear portions of curves (ahv)2 = f(hv) for (ahv)2 - 0. For the analised samples these values (Eg = 2.68 – 3.5eV) are in a good agreement with the values of band gap energy obtained for bulk crystals.
În lucrare sunt prezentate rezultatele cercetării termoluminiscenţei straturilor subţiri policris... more În lucrare sunt prezentate rezultatele cercetării termoluminiscenţei straturilor subţiri policristaline de ZnSe. Dependenţa spectrală a termoluminiscenţei este formată din două maxime, primul cel mai intens la T max = 153K şi al doilea la T max = 216K. Valorile energiei de ionizare a nivelelor de captură, E t , determinate din această dependenţă, sunt egale cu 0.062eV şi 0.44eV de la marginea inferioară a benzii de conducţie, iar nivelul de localizare a centrelor de recombinarela 0.66eV de la marginea superioară a benzii de valenţă.
The paper presents photovoltaic materials and modern technologies of preparation of excitonic sol... more The paper presents photovoltaic materials and modern technologies of preparation of excitonic solar cells type ITO/PEDOT:PSS/CH3NH3PbI3/PC61BM/Ag.
International Journal of Modern Physics B, 2004
Cadmium sulfide (CdS) thin films (d=0.15–1.15 μ m ) were deposited onto glass substrates by the q... more Cadmium sulfide (CdS) thin films (d=0.15–1.15 μ m ) were deposited onto glass substrates by the quasi-closed volume technique under vacuum. The investigations shown that the films are polycrystalline and have a hexagonal structure. It was experimentally established that the films with stable structure can be obtained if they are submitted to a heat treatment, consisting of several succesive heating/cooling cycles within a given temperature range (ΔT=300–600 K ), the temperature dependence of the electrical conductivity becomes reversible. For heat-treated samples, the values of thermal activation energy calculated from the temperature dependence of the electrical conductivity, ranged between 2.30–2.45 eV. The spectral dependences of the transmission and absorption coefficients were studied in the range 500–1400 nm. The influence of heat treatment on the shape of the absorption spectra and dispersion index of refraction is studied for samples with different thickness. Optical energy ...
Applied Surface Science, 2007
Zeolitic imidazolate frameworks (ZIF-8) thin films were fabricated via layer by a layer depositio... more Zeolitic imidazolate frameworks (ZIF-8) thin films were fabricated via layer by a layer deposition method. The investigation of X-ray diffraction (XRD) of the ZIF-8 powder form was seen to be polycrystalline with a single cubic-phase structure. The lattice parameters and Miller index were calculated using Rietveld refinement by Fullprof software. XRD of ZIF-8 film demonstrates an amorphous structure. The morphology of the ZIF-8 films has therefore been studied with the scanning laser microscope method and found that the homogeneity and surface enhance with increasing the film thickness. On the other hand, it is found that ZIF-8 films have a direct electronic transition with two energy bandgaps (3.62 and 4.58 eV) and their values independent of the thickness of the films. The optical constants were calculated, and the refractive index esteems increment with expanding of the film thickness. This outcome might be credited to the interlude of the film in the preliminary phase of the deposition. The nonlinear optical constants for ZIF-8 film were calculated, and the third-order optical nonlinearity was expanded with expanding the film thickness.
Applied Surface Science, 2003
Zinc selenide (ZnSe) thin films were deposited onto glass substrates by the quasi-closed volume t... more Zinc selenide (ZnSe) thin films were deposited onto glass substrates by the quasi-closed volume technique under vacuum. The film structure was studied by X-ray diffraction (XRD) technique, scanning electron microscopy and atomic force microscopy (AFM). The ...
Studia Universitatis Moldaviae: Stiinte Exacte si Economice, 2019
În lucrare sunt prezentate rezultatele experimentale obținute la aplicarea PEDOT-PSS în calitate ... more În lucrare sunt prezentate rezultatele experimentale obținute la aplicarea PEDOT-PSS în calitate de strat de transport de goluri și a PC61BM ca strat de transport de electroni în celule solare de perovskite cu arhitectură plană inversată. Aceste dispozitive au atins o eficiență maximă a puterii de conversie (PCE) de aproximativ 19,27%. Celulele solare în care s-a preparat heterojuncțiunea voluminoasă din perovskit (CH3NH3PbI3) dopat cu PC61BM au înregistrat un randament maxim de aproximativ 23,59%. Cuvinte-cheie: celulă solară, PEDOT-PSS, PC61BM, densitate de curent, tensiune. PEROVSKI SOLAR CELLS WITH HIGH POWER CONVERSION EFFICIENCY The experimental results obtained by applying PEDOT-PSS as a hole transport layer and PC61BM as a electron transport layer in perovskite solar cells with inverted planar architecture are presented in the work. These devices have reached a maximum power conversion efficiency (PCE) of about 19.27%. Solar cells in which bulk heterojunction was prepared from perovskite (CH3NH3PbI3) doped with PC61BM have registered a maximum PCE of approximately 23.59 %.
The work treats different aspects of the philosophy of exploring the cosmos, stages of rocket tec... more The work treats different aspects of the philosophy of exploring the cosmos, stages of rocket technology development and practical applications of cosmonautics.
In the work were presented preparation and research techniques of the electrical properties of th... more In the work were presented preparation and research techniques of the electrical properties of the perovskite solar cells, in which ZnS, ZnSe and ZnTe thin films were applied. Using these layers as the electron transport layer (ETL), a power conversion efficiency (PCE) of about 2.57% was obtained, and cells with hole transport layer (HTL) the PCE achieved a maximum 2.14%. By doping ETL and HTL with chalcogenides a maximum yield of 3.98% was obtained. Preparation of solar cells with two layers of ETL or HTL increased of PCE to 7.40% maximum. By doping bulk heterojunction of perovskite with the calcogenide thin layers has increased PCE of cells up to 13.84%.
The ZnSxSe1-x thin films were deposited by the quasi-closed volume technique under vacuum. The fi... more The ZnSxSe1-x thin films were deposited by the quasi-closed volume technique under vacuum. The film structure was studied by X-ray diffraction technique. The studies shown the films are polycrystalline and have a zinc blende structure. The spectral dependences of transmission, reflection, absorption and refraction index were studied. Values of band gap energy determined from the reflectance and absorption spectra are in good agreement with the theoretical values Eg.
Spectroscopic technique is very useful for characterising semiconducting materials. We demonstrat... more Spectroscopic technique is very useful for characterising semiconducting materials. We demonstrate here a new method for determination the energy band gap of thin fims from reflectance data.
The reflection and transmission spectra (in the range from 300nm to 1400nm) were recorded using a... more The reflection and transmission spectra (in the range from 300nm to 1400nm) were recorded using a PMQ – II (Carl Zeiss, Jena) spectrophotometer. The absorption coefficient, was determined from transmission spectra. The values of optical band gap, Eg, have been determined by extrapolating the linear portions of curves (ahv)2 = f(hv) for (ahv)2 - 0. For the analised samples these values (Eg = 2.68 – 3.5eV) are in a good agreement with the values of band gap energy obtained for bulk crystals.
În lucrare sunt prezentate rezultatele cercetării termoluminiscenţei straturilor subţiri policris... more În lucrare sunt prezentate rezultatele cercetării termoluminiscenţei straturilor subţiri policristaline de ZnSe. Dependenţa spectrală a termoluminiscenţei este formată din două maxime, primul cel mai intens la T max = 153K şi al doilea la T max = 216K. Valorile energiei de ionizare a nivelelor de captură, E t , determinate din această dependenţă, sunt egale cu 0.062eV şi 0.44eV de la marginea inferioară a benzii de conducţie, iar nivelul de localizare a centrelor de recombinarela 0.66eV de la marginea superioară a benzii de valenţă.
The paper presents photovoltaic materials and modern technologies of preparation of excitonic sol... more The paper presents photovoltaic materials and modern technologies of preparation of excitonic solar cells type ITO/PEDOT:PSS/CH3NH3PbI3/PC61BM/Ag.
International Journal of Modern Physics B, 2004
Cadmium sulfide (CdS) thin films (d=0.15–1.15 μ m ) were deposited onto glass substrates by the q... more Cadmium sulfide (CdS) thin films (d=0.15–1.15 μ m ) were deposited onto glass substrates by the quasi-closed volume technique under vacuum. The investigations shown that the films are polycrystalline and have a hexagonal structure. It was experimentally established that the films with stable structure can be obtained if they are submitted to a heat treatment, consisting of several succesive heating/cooling cycles within a given temperature range (ΔT=300–600 K ), the temperature dependence of the electrical conductivity becomes reversible. For heat-treated samples, the values of thermal activation energy calculated from the temperature dependence of the electrical conductivity, ranged between 2.30–2.45 eV. The spectral dependences of the transmission and absorption coefficients were studied in the range 500–1400 nm. The influence of heat treatment on the shape of the absorption spectra and dispersion index of refraction is studied for samples with different thickness. Optical energy ...
Applied Surface Science, 2007
Zeolitic imidazolate frameworks (ZIF-8) thin films were fabricated via layer by a layer depositio... more Zeolitic imidazolate frameworks (ZIF-8) thin films were fabricated via layer by a layer deposition method. The investigation of X-ray diffraction (XRD) of the ZIF-8 powder form was seen to be polycrystalline with a single cubic-phase structure. The lattice parameters and Miller index were calculated using Rietveld refinement by Fullprof software. XRD of ZIF-8 film demonstrates an amorphous structure. The morphology of the ZIF-8 films has therefore been studied with the scanning laser microscope method and found that the homogeneity and surface enhance with increasing the film thickness. On the other hand, it is found that ZIF-8 films have a direct electronic transition with two energy bandgaps (3.62 and 4.58 eV) and their values independent of the thickness of the films. The optical constants were calculated, and the refractive index esteems increment with expanding of the film thickness. This outcome might be credited to the interlude of the film in the preliminary phase of the deposition. The nonlinear optical constants for ZIF-8 film were calculated, and the third-order optical nonlinearity was expanded with expanding the film thickness.
Applied Surface Science, 2003
Zinc selenide (ZnSe) thin films were deposited onto glass substrates by the quasi-closed volume t... more Zinc selenide (ZnSe) thin films were deposited onto glass substrates by the quasi-closed volume technique under vacuum. The film structure was studied by X-ray diffraction (XRD) technique, scanning electron microscopy and atomic force microscopy (AFM). The ...
Studia Universitatis Moldaviae: Stiinte Exacte si Economice, 2019
În lucrare sunt prezentate rezultatele experimentale obținute la aplicarea PEDOT-PSS în calitate ... more În lucrare sunt prezentate rezultatele experimentale obținute la aplicarea PEDOT-PSS în calitate de strat de transport de goluri și a PC61BM ca strat de transport de electroni în celule solare de perovskite cu arhitectură plană inversată. Aceste dispozitive au atins o eficiență maximă a puterii de conversie (PCE) de aproximativ 19,27%. Celulele solare în care s-a preparat heterojuncțiunea voluminoasă din perovskit (CH3NH3PbI3) dopat cu PC61BM au înregistrat un randament maxim de aproximativ 23,59%. Cuvinte-cheie: celulă solară, PEDOT-PSS, PC61BM, densitate de curent, tensiune. PEROVSKI SOLAR CELLS WITH HIGH POWER CONVERSION EFFICIENCY The experimental results obtained by applying PEDOT-PSS as a hole transport layer and PC61BM as a electron transport layer in perovskite solar cells with inverted planar architecture are presented in the work. These devices have reached a maximum power conversion efficiency (PCE) of about 19.27%. Solar cells in which bulk heterojunction was prepared from perovskite (CH3NH3PbI3) doped with PC61BM have registered a maximum PCE of approximately 23.59 %.
The work treats different aspects of the philosophy of exploring the cosmos, stages of rocket tec... more The work treats different aspects of the philosophy of exploring the cosmos, stages of rocket technology development and practical applications of cosmonautics.
In the work were presented preparation and research techniques of the electrical properties of th... more In the work were presented preparation and research techniques of the electrical properties of the perovskite solar cells, in which ZnS, ZnSe and ZnTe thin films were applied. Using these layers as the electron transport layer (ETL), a power conversion efficiency (PCE) of about 2.57% was obtained, and cells with hole transport layer (HTL) the PCE achieved a maximum 2.14%. By doping ETL and HTL with chalcogenides a maximum yield of 3.98% was obtained. Preparation of solar cells with two layers of ETL or HTL increased of PCE to 7.40% maximum. By doping bulk heterojunction of perovskite with the calcogenide thin layers has increased PCE of cells up to 13.84%.
The ZnSxSe1-x thin films were deposited by the quasi-closed volume technique under vacuum. The fi... more The ZnSxSe1-x thin films were deposited by the quasi-closed volume technique under vacuum. The film structure was studied by X-ray diffraction technique. The studies shown the films are polycrystalline and have a zinc blende structure. The spectral dependences of transmission, reflection, absorption and refraction index were studied. Values of band gap energy determined from the reflectance and absorption spectra are in good agreement with the theoretical values Eg.