Numerical analysis for efficiency enhancement of thin film solar cells

[ES] Desde hace una década se esta investigando intensamente la forma de mejorar la eficiencia de conversión de energía (PCE) de las células solares de silicio (Si) y reducir sus precios. Sin embargo, a pesar de las mejoras obtenidas, la fabricación de células solares de Si sigue siendo costosa y puede rebajarse usando materiales en forma de capa fina. Por ello la búsqueda de materiales absorbentes alternativos, no tóxicos, abundantes en la naturaleza y con buenos rendimientos de conversión se ha intensificado en los últimos años. Entre los diferentes materiales absorbentes el sulfuro de estaño (SnS), con una banda prohibida de 1.3 eV cercana a la óptima, es un candidato adecuado para la conversión fotovoltaica. Pero para células experimentales de SnS el rendimiento alcanzado hasta ahora es de 4.6%, que es mucho menos que el PCE para dispositivos de silicio, mientras que entre otras células híbridas (orgánicas-no orgánicas) como la perovskita de metilamonio de plomo y yodo (MAPbI3) se demuestra que es un candidato adecuado con PCE que alcanza un valor del 23%. Aparte de la estabilidad, uno de los problemas para la comercialización de células de MAPbI3 es la naturaleza tóxica del plomo (Pb). Por este motivo, se ha utilizado el análisis numérico para revisar los parámetros de diseño de las células solares de perovskita híbrida sustituyendo el absorbente MAPbI3 por MASnI3 y estudiar el efecto del resto de parámetros de diseño en el rendimiento de estas células solares. Hay varios softwares de simulación disponibles que se utilizan para el análisis numérico de células solares. En este trabajo hemos usamos un software llamado "A Solar Cell Capacitance Simulator" (SCAPS), está disponible de forma gratuita y es muy popular entre la comunidad científica y tecnológica. Para lograr un diseño efectivo para una célula solar eficiente, se propuso una aproximación numérica basada en la mejora de la PCE de una célula solar experimental. Esto se hizo reproduciendo los resultados para la célula solar diseñada experimentalmente en un entorno SCAPS con estructura p-SnS / n-CdS con una eficiencia de conversión del 1,5%. Después de la reproducción de los resultados experimentales, el rendimiento del dispositivo se optimizó ajustando el grosor de la capa absorbente y la capa tampón, la el tiempo de vida de los portadores minoritarios, la concentración del dopado en las capas absorbente, tampón y en la capa de la ventana. Mediante la optimización gradual de los parámetros del dispositivo, se alcanzó un valor de 14.01% en PCE de células solares diseñadas con SCAPS con arquitectura p-SnS / n-CdS / n-ZnO. A partir del análisis, se encontró que la PCE de una célula solar depende en gran medida de la concentración de dopaje de la capa absorbente, el espesor de la capa absorbente y los defectos de la interfaz. Sobre la base de los resultados obtenidos, se realizó un análisis para determinar el efecto de la recombinación de la interfaz en el rendimiento de las células solares y cómo se puede controlar. Para realizar esta tarea, se realizó un análisis para la selección de la capa tampón adecuada para la célula solar de perovskita metilamonio de estaño y yodo (MASnI3) y se encontró que el PCE de la célula solar también depende de la alineación de la banda entre el absorbedor y la capa de tampón. Por otra parte, se ha propuesto una nueva estructura para la célula solar de perovskita libre de Pb (contacto posterior / MASnBr3 / MASnI3 /CdZnS / FTO) con un PCE de 18.71% para un espesor del absorbedor de 500 nm y una concentración de dopado en el aceptor de 1x1016 cm-3. Los resultados obtenidos en esta tesis proporcionarán una guía para que los investigadores experimentales puedan construir células solares más eficientes.[CA] Des de fa una dècada s'està investigant intensament la forma de millorar l'eficiència de conversió d'energia (PCE) de les cèl·lules solars de silici (Si) i reduir els seus preus. No obstant això, tot i les millores obtingudes, la fabricació de cèl·lules solars de Si segueix sent costosa i pot rebaixar-se usant materials en forma de capa fina. Per això la recerca de materials absorbents alternatius, no tòxics, abundants en la naturalesa i amb bons rendiments de conversió s'ha intensificat en els últims anys. Entre els diferents materials absorbents, el sulfur d'estany (SnS), amb una banda prohibida de 1.3 eV propera a l'òptima, és un candidat adequat per a la conversió fotovoltaica. Però per a cèl·lules experimentals de SnS el rendiment assolit fins ara és de 4.6%, que és molt menor que el PCE per a dispositius de silici, mentre que entre altres cèl·lules híbrides (orgàniques-no orgàniques) com la perovskita de metilamonio de plom i iode ( MAPbI3) es demostra que és un candidat adequat amb PCE que arriba a un valor del 23%. A part de l'estabilitat, un dels problemes per a la comercialització de cèl·lules de MAPbI3 és la naturalesa tòxica del plom (Pb). Per aquest motiu, s'ha utilitzat l'anàlisi numèrica per revisar els paràmetres de disseny de les cèl·lules solars de perovskita híbrida substituint l'absorbent MAPbI3 per MASnI3 i estudiar l'efecte de la resta de paràmetres de disseny en el rendiment d'estes cèl·lules solars. Hi ha diversos programaris de simulació disponibles que s'utilitzen per a l'anàlisi numèric de cèl·lules solars. En aquest treball hem fem servir un programari anomenat "A Solar Cell Capacitance Simulator" (SCAPS), està disponible de forma gratuïta i és molt popular entre la comunitat científica i tecnològica. Per aconseguir un disseny efectiu per a una cèl·lula solar eficient, es va proposar una aproximació numèrica basada en la millora de la PCE d'una cèl·lula solar experimental. Això es va fer reproduint els resultats per a la cèl·lula solar dissenyada experimentalment en un entorn SCAPS amb estructura p-SnS / n-CdS amb una eficiència de conversió de l'1,5%. Després de reproduir els resultats experimentals, el rendiment del dispositiu es va optimitzar ajustant el gruix de la capa absorbent y de la capa tampó, el temps de vida dels portadors minoritaris, la concentració del dopatge en les capes absorbent, tampó i en la capa finestra. Mitjançant l'optimització gradual dels paràmetres del dispositiu, es va assolir un valor de 14.01% en PCE de cèl·lules solars dissenyades experimentalment en SCAPS amb arquitectura p-SnS / n-CdS / n-ZnO. A partir de l'anàlisi, es va trobar que la PCE d'una cèl·lula solar depèn en gran mesura de la concentració de dopatge de la capa absorbent, el gruix de la capa absorbent i els defectes de la interfície. D'altra banda, es va realitzar una anàlisi per determinar l'efecte de la recombinació de la interfície en el rendiment de les cèl·lules solars i com es pot controlar. Per realitzar aquesta tasca, es va realitzar una anàlisi per a la selecció de la capa tampó adequada per a la cèl·lula solar de perovskita de metilamoni d'estany i iode (MASnI3) i es va trobar que el PCE de la cèl·lula solar també depèn de l'alineació de la banda entre l'absorbidor i la capa de tampó.[EN] A decade of extensive research has been conducted to enhance the power conversion efficiency (PCE) of silicon (Si) solar cells and to cut their prices short. But still, the fabrication of Si solar cells are costly. So, to reduce the fabrication cost of the solar cell search for alternate earth abundant and non-toxic absorber materials is thriving. Among different absorber materials tin sulfide (SnS) is found to be a suitable candidate for the non-organic solar cell with a band gap of 1.3 eV. But the PCE achieved for SnS is 4.6% that is far less from the PCE of (Si), whereas among other organic non-organic solar cells like methylammonium lead halide perovskite ({\rm MAPbI}_3) is proven to be a suitable candidate with PCE reaching to a value of 23%. The problem with the commercialization of {\rm MAPbI}_3 is due to the toxic nature of lead (Pb). So, in dealing with these issues of solar cell numerical analysis can play a key role as numerical analysis allows flexibility in the design of realistic problem and experimentation with different hypotheses can easily be performed. Complete set of device characteristic can often be easily generated by consuming less amount of time and effort. Because of this reason numerical analysis was used to revisit solar cells design parameters and the effect of solar cell physical parameters on solar cell performance. There are various simulation software's available that are used for solar cell numerical analysis. Here in this work, we used Solar cell capacitance simulator (SCAPS) software, it is freely available and is most popular among the research community. To achieve effective design for efficient solar cell a numerical guide was proposed based on which PCE of an experimental designed solar cell can be enhanced. This was done by reproducing results for the experimentally designed solar cell in SCAPS environment with structure p-SnS/n-CdS having a conversion efficiency of 1.5%. After reproduction of experimental results device performance was optimized by varying thickness of (absorber layer, buffer layer), minority carrier lifetime, doping concentration (absorber, buffer), and adding window layer. By stepwise optimization of device parameters, PCE of an experimental designed solar cell in SCAPS with architecture p-SnS/n-CdS/n-ZnO was reached to a value of 14.01%. From the analysis, it was found that PCE of a solar cell is highly depended upon doping concentration of the absorber layer, the thickness of the absorber layer and interface defects. Based on the results evaluated an analysis was performed for tin based organic non-organic methylammonium tin halide perovskite solar cell ({\rm MASnI}_3) to find the effect of interface recombination on solar cell performance and how it can be governed. The reason for this transition from SnS to {\rm MASnI}_3 was because {\rm MASnI}_3 can be fabricated simply by spin-coating methylammonium iodide (MAI) over SnS layer. To perform this task analysis was performed for the selection of suitable buffer layer for Pb free methylammonium tin halide perovskite solar cell ({\rm MASnI}_3) and it was found that PCE of the solar cell is also depended upon band alignment between absorber and buffer layer. Based on the results a new structure was proposed for Pb free perovskite solar cell (Back\ contact/{\rm MASnBr}_3/{\rm MASnI}_3/CdZnS/FTO) with PCE of 18.71% for absorber thickness of 500 nm and acceptor doping concentration of 1x10^{16}\ {\rm cm}^3. The results achieved in this thesis will provide an imperative guideline for researchers to design efficient solar cells.Baig, F. (2019). Numerical analysis for efficiency enhancement of thin film solar cells [Tesis doctoral no publicada]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/118801TESI

Regeneration mechanisms of organized structures in near-wall turbulence

We have performed direct numerical simulations (DNS) of quasi-2D (that is with flow parameters independent of longitudinal coordinate) decaying and forced turbulence and 3D turbulent channel flows in order to ascertain the sustenance mechanism of near-wall turbulence by investigating the mechanism of streak formation. We found the existence of streaks in quasi-2D flows thus demonstrating that contrary to many proposed theories, feedback from longitudinal flow is not necessary for streak formation. Passive scalars having different mean scalar profiles were introduced in forced quasi-2D and 3D turbulent flows in order to compare the streak spacing of the scalars deduced from two-point correlations of DNS results with results obtained theoretically.It has been found that even for the same vortex structure for all the passive scalars there is a marked variation in streak spacing implying that the preferential streak spacing is not necessarily equal to twice the vortex spacing, as has been suggested by several proposed theories. Moreover, the formation of scalar streaks in a velocity field prescribed as s sum of a mean turbulent velocity profile and random potential perturbations, conclusively supports the fact that organised vortices are not needed for generation of near-wall streaks. It has also been demonstrated that the lift-up mechanism responsible for generation of streaks is also responsible for the cross-flow spacing. The obtained qualitative numerical results are in favour of theory of streak formation based on optimal perturbations (Butler and Farrell, 1993) but at the same time the quantitative agreement is poor. So a modification of the same - Generalized optimal perturbation (Chernyshenko and Baig, 2003) theory has been proposed and it offers significantly better agreement with the DNS results

Use of follicular output rate to predict intracytoplasmic sperm injection outcome

Background: The measurement of follicular output rate (FORT) has been proposed as a good indicator for evaluating follicular response to the exogenous recombinant folliclestimulating hormone (rFSH). This places FORT as a promising qualitative marker for ovarian function. The objective of the study was to determine FORT as a predictor of oocyte competence, embryo quality and clinical pregnancy after intracytoplasmic sperm injection (ICSI).Materials and Methods: This prospective study was carried out on a group of infer- tile females (n=282) at Islamabad Clinic Serving Infertile Couples, Islamabad, Pakistan, from June 2010 till August 2013. Downregulated females were stimulated in injection gonadotropins and on ovulation induction day, pre-ovulatory follicle count (PFC) was determined using transvaginal ultrasound scan (TVUS), and FORT was determined as a ratio of PFC to antral follicle count (AFC)*100. Group I consisted of females with a negative pregnancy test, while group II had a positive pregnancy test that was confirmed with the appearance of fetal cardiac activity. Linear regression analyses of categorical variables of clinical pregnancy along with other independent variables, including FORT, were performed using SPSS version 15.0.Results: Pregnancy occurred in 101/282 women who were tested, recording a clinical pregnancy rate of about 35.8%. FORT values were higher in group II as compared to group I females (P=0.0001). In multiple regression analysis, 97.7, 87.1, 78.2, and 83.4% variations were explained based on the number of retrieved oocytes per patients, number of metaphase II oocytes retrieved, number of fertilized oocytes, and number of cleaved embryos, respectively, indicating FORT as an independent predictor.Conclusion: FORT is a predictor of oocyte competence in terms of a number of retrieved, mature and fertilized oocytes. It also gives information about the number of cleaved embryos and clinical pregnancy rate

Numerical Modeling Baseline for high efficiency (Cu2FeSnS4) CFTS based Thin Film Kesterite Solar Cell

[EN] Cu2FeSnS4 (CFTS) is auspicious nontoxic and earth abundant semiconductor compound having kesterite symmetrical structure. It is an attractive and suitable material for the fabrication of low cost, high efficiency and sustainable thin film photovoltaic cell. ¿¿¿¿¿¿¿¿ based kesterite photovoltaic cell device modeling was performed in this work. The influence of device parameters such as the thickness, acceptor and donor carrier concentration densities of absorber and electron transport layer (ETL), effect of back contact metal work function and the temperature effect on the performance of ¿¿¿¿¿¿¿¿ based kesterite photovoltaic cell is analyzed by using one dimensional solar cell capacitance simulator (SCAPS) software. In this work, promising optimized results had been achieved with the conversion efficiency of 19.97%, fill factor (¿¿¿¿) 85.94 %, short-circuit current (¿¿¿¿¿¿ ) 23.37 ¿¿¿¿/¿¿¿ 2 and open circuit voltage (¿¿¿¿¿¿ ) 0.995V. The above results will give imperative baselines and feasible directions for the fabrication of higher efficiency ¿¿¿¿¿¿¿¿ based photovoltaic cellThis work was supported by Ministerio de Economia y Competitividad (ENE2016-77798-C4-2-R) and Generalitat valenciana (Prometeus 2014/044).Khattak, YH.; Baig, F.; Ullah, S.; Marí, B.; Ullah, H. (2018). Numerical Modeling Baseline for high efficiency (Cu2FeSnS4) CFTS based Thin Film Kesterite Solar Cell. Optik - International Journal for Light and Electron Optics. 164:547-555. https://doi.org/10.1016/j.ijleo.2018.03.055S54755516

The Impact of COVID-19 Pandemic on Final Year Medical Students: Single Center Study

Introduction: The COVID-19 health emergency led to adoption of unprecedented measures that have never been seen in recent times. The study examines the effect of COVID-19 on final year medical students’ final professional examination preparedness, transition to house job and earlier assistantship.Methodology: This descriptive cross-sectional survey was conducted in September – October 2020 after institutional review board approval at University College of Medicine and Dentistry (UCMD) in Lahore, Pakistan. A total of 112 final year medical students responded to this survey whereas 13 did not. Data was analyzed using SPSS 25. Chi square test was applied to evaluate the impact of COVID 19 on variables of interest (p-value< 0.05 considered significant). Results: Postponement of clinical rotations, written exams, OSPEs and clinical ward tests was reported by 62%, 78%, 71% and 48% students respectively whilst 29%, 13%, 18% and 21% students respectively stated it to be formatted. A statistically significant impact (p<0.05) was observed for final professional examinations preparedness and confidence to assist earlier.Conclusion: The study demonstrated the significant impact of COVID-19 on final year medical students’ examination preparedness and confidence to assist earlier in hospital. Improvised teaching methodology is urgently needed to fill in the lapses in their education.Keywords: COVID-19, Medical Education, Final year MBBS professional examination, OSPE, Earlier Assistantship, House Job

Banti\u27s syndrome: case report and review of literature.

In 1898 Banti described a disorder characterized by splenomegaly and hypersplenism, resulting in portal hypertension and anemia in the absence of hematological disease. 1 Banti\u27s syndrome is also known as non-cirrhotic portal hypertension (NCPH) in India and Idiopathic Portal Hypertension (IPH) in Japan. Hepatoportal sclerosis seems to be its counterpart in the United States. 2,3 Banti\u27s syndrome is a disorder of unknown etiology, clinically characterized by portal hypertension (varices and portosystemic collateral vessels), splenomegaly, and anemia (hypersplenism). 3 It has been reported from Indian subcontinent. 4-6 In a Pakistani case series of portal hypertension, 18 out of 37 patients were found to have IPH as the etiology. 6 We report a case of Banti\u27s syndrome in an 20-year old girl presenting to us with anemia and splenomegaly

Modelling of novel-structured copper barium tin sulphide thin film solar cells

[EN] In this work, a novel structured Cu2BaSnS4 (CBTS)/ZnS/Zn(O, S) photovoltaic device is proposed. A nontoxic, earth-abundant and auspicious quaternary semiconductor compound copper barium tin sulphide (Cu2BaSnS4) is used as an absorber layer. We propose a novel Zn(O, S) buffer layer for a high-power conversion efficiency (PCE) of CBTS-based thin film photovoltaic cells. Solar cell capacitance simulator software is used for device modelling and simulations are performed under a 1.5 AM illumination spectrum. The proposed device is investigated by means of numerical modelling and optimized the parameters to maximize its efficiency. Promising optimized functional parameters had been achieved from the proposed structure with back surface field layer with a PCE of 18.18%, a fill factor of 83.45%, a short-circuit current of 16.13 mA cm¿2 and an open-circuit voltage of 1.3 V. The promising results give an imperative standard for possible manufacturing of high efficiency, eco-friendly inorganic CBTS-based photovoltaic cells.This work was supported by Ministerio de Economia y Competitividad (ENE2016-77798-C4-2-R) and Generalitat valenciana (Prometeus 2014/044).Hameed, KY.; Baig, F.; Toura, H.; Marí, B.; Beg, S.; Khani, NAK. (2019). Modelling of novel-structured copper barium tin sulphide thin film solar cells. Bulletin of Materials Science. 42(5):1-8. https://doi.org/10.1007/s12034-019-1919-9S18425Ge J, Koirala P, Grice C R, Roland P J, Yu Y, Tan X et al 2017 Adv. Energy Mater. 7 1601803Khattak Y H, Mahmood T, Alam K, Sarwar T, Ullah I and Ullah H 2014 Am. J. Electr. Power Energy Syst. 3 86Steinmann V, Brandt R E and Buonassisi T 2015 Nat. Photonics 9 355Jackson P, Hariskos D, Wuerz R, Kiowski O, Bauer A, Friedlmeier T M et al 2015 Phys. Status Solidi: Rapid. Res. Lett. 9 28Shin D, Saparov B and Mitzi D B 2017 Adv. Energy Mater. 7 1602366Paper C, Le A, Universit D, Universit B, Universit M A, Marchionna S et al 2017 Eur. Photovolt. Sol. Energy Conf. 33 25Khattak Y H, Baig F, Ullah S, Marí B, Beg S and Ullah H 2018 J. Renew. Sustain. Energy 10 033501Fontané X, Izquierdo-Roca V, Saucedo E, Schorr S, Yukhymchuk V O, Valak M Y et al 2012 J. Alloys Compd. 539 190Zhang X, Bao N, Ramasamy K, Wang Y-H A, Yifeng Wang B L and Gupta A 2012 Chem. Commun. 48 4956Adewoyin A D, Olopade M A and Chendo M 2017 Optik—Int. J. Light Electron Opt. 133 122Boutebakh F Z, Zeggar M L, Attaf N and Aida M S 2017 Optik—Int. J. Light Electron Opt. 144 180Ananthakumar S, Ram Kumar J and Moorthy Babu S 2016 Optik—Int. J. Light Electron Opt. 127 10360Jianjun L, Dongxiao W, Xiuling L and Zeng Y 2018 Adv. Sci. 5 1700744Khattak Y H, Baig F, Ullah S, Marí B, Beg S and Ullah H 2018 Optik—Int. J. Light Electron Opt. 164 547Xiao Z, Meng W, Li J V. and Yan Y 2017 ACS Energy Lett. 2 29Shin D, Saparov B, Zhu T, Huhn W P, Blum V and Mitzi D B 2016 Chem. Mater. 28 477Repins I L, Romero M J, Li J V, Wei S-H, Kuciauskas D, Jiang C-S et al 2013 J. Photovoltaics 3 439Zhou H, Hsu W-C, Duan H-S, Bob B, Yang W, Song T-B et al 2013 Energy Environ. Sci. 6 2822Khattak Y H, Baig F, Toura H, Ullah S, Marí B, Beg S et al 2018 Curr. Appl. Phys. 18 633Ge J, Roland P J, Koirala P, Meng W, Young J L, Petersen R et al 2017 Chem. Mater. 29 916Ge J and Yan Y 2017 J. Mater. Chem. C 5 6406Hong F, Lin W, Meng W and Yan Y 2016 Phys. Chem. Chem. Phys. 18 4828Todorov T, Gunawan O and Guha S 2016 Mol. Syst. Des. Eng. 1 370Baig F, Ullah H, Khattak Y H and Mari Soucase B 2016 Int. Ren. Sus. En. Conf. 596, https://doi.org/10.1109/IRSEC.2016.7983899Lin L-Y, Qiu Y, Zhang Y and Zhang H 2016 Chinese Phys. Lett. 33 10780Platzer B C, Törndahl T, Abou-Ras D, Malmström J, Kessler J and Stolt L 2006 J. Appl. Phys. 100 044506Persson C, Platzer-Björkman C, Malmström J, Törndahl T and Edoff M 2006 Phys. Rev. Lett. 97 146403Burgelman M, Nollet P and Degrave S 2000 Thin Solid Films 361 527Khattak Y H, Baig F, Soucase B M and Beg S 2018 Mater. Focus 84 758Simya O K, Mahaboobbatcha A and Balachander K A 2015 Superlattices Microstruct. 82 248Shin D, Zhu T, Huang X, Gunawan O, Blum V and Mitzi D B 2017 Adv. Mater. 29 1Saha U and Alam M K 2018 Phys. Status Solidi: Rapid Res. Lett. 12 1Zhu T, Huhn W P, Wessler G C, Shin D, Saparov B, Mitzi D B et al 2017 Chem. Mater. 29 7868Ge J, Grice C R and Yan Y 2017 J. Mater. Chem. A 5 2920Baig F, Khattak Y H, Marí B, Beg S, Gillani S R and Ahmed A 2018 Optik—Int. J. Light Electron Opt. 170 463Khattak Y H, Baig F, Ullah S, Marí B, Beg S and Gillani S R 2018 Optik—Int. J. Light Electron Opt. 171 45