DESIGN AND ANALYSIS OF MULTILAYERED ORGANIC SOLAR CELL FOR BIOMEDICAL APPLICATION

Abstract

The present work delves into the research, development, and optimization of solar cell technology for energy harvesting and biomedical applications. This research focuses on two key areas: improving solar cell efficiency and integrating solar cells into biomedical devices. The goal is to improve the performance of solar cells and investigate their potential in healthcare challenges. The work analyses the use of Sb (Antimony) and Sn (Tin) doped Zinc Telluride (ZnTe) thin films as absorber layers in multi-layered solar cells. The films are synthesised using a low-cost melt-quenching technique and then analysed using X-ray diffraction (XRD). The electrical characteristics and parameters for ZnTe, SbZnTe and SnZnTe materials are analysed. Further, based on the extracted properties, these materials are utilized as the absorber layer in the solar cell. Additionally, the performance of SbZnTe and SnZnTe based solar cells is compared against the ZnTe material based solar cell. Illustrating the behaviour of absorber layer materials internally, these solar cells are analysed through horizontal and vertical cut-lines, wherein, it is observed that SnZnTe cell has reasonably higher hole and electron carrier concentrations. The current density for SnZnTe based solar cell is obtained higher by 2.3 and 2.6 times than that of SbZnTe and ZnTe based cells, respectively at the thickness of 1.5 μm. The Fill Factor for SnZnTe cell is obtained as 84.66%, which is also reasonably higher than the fill factor of 59.66% obtained for SbZnTe and 56.66% for ZnTe based solar cell. Further the efficiency with 17.8% is highest for SnZnTe, which is followed by SbZnTe with 10.6%. The efficiency of 9.2% is lowest for ZnTe. The current density of SbZnTe and SnZnTe solar cells is significantly higher than that of ZnTe solar cell, with enhancements of 1.1 and 2.6 times, respectively, at 1.5 µm absorber thickness. Furthermore, a comparison of the different solar cell layers shows that SnZnTe demonstrates superior performance due to its lowest band gap and higher charge carrier generation. Hence, it is found that the SnZnTe material is best suits as the absorber material. Therefore, the absorber layer is found instrumental in improving the device performance without increasing the dimensions of the device. The focus of the work further moves towards optimization and efficiency enhancement of organic solar cells. The P3HT: PCBM bilayer organic solar cell is analysed internally to determine carrier concentration, electric field distribution, and electron/hole current density in v the constituent layers. The effect of donor and acceptor layer thicknesses on the solar cell performance is investigated, and an optimised efficiency of 0.90% is obtained. To further enhance the efficiency, the donor layer material is changed from P3HT (poly(3- hexylthiophene-2,5-diyl)) to PTB7 (Poly[[4,8-bis[(2-ethylhexyl)oxy]benzo[1,2-b:4,5- b’]dithiophene-2,6-diyl][3-fluoro-2-[(2-ethylhexyl)carbonyl]thieno[3,4-b]thiophenediyl]], which increases the efficiency to 1.33 %. Furthermore, a Poly(3,4-ethylenedioxythiophene)- poly(styrenesulfonate) (PEDOT: PSS) hole transport layer (HTL) is added for efficiency enhancement up to 1.55%. It is followed by an addition of Poly [(9,9-bis(3’-(N,N dimethylamino)propyl-2,7-fluorene)-alt-2,7-(9,9-dioctylfluorene)] (PFN) electron transport layer (ETL) which enhanced the efficiency to 1.91%. Subsequently, an inverted structure for the modified solar cell is analysed, which further enhanced the efficiency to 2.08%. Further, a comparative study for conventional and inverted structure of solar cell is executed. The solar cell performs optimum at a donor and acceptor thickness of 40 nm and 50 nm respectively. Addition of HTL and ETL increases the performance of solar cell significantly so does the change of donor material from P3HT to PTB7, a low band gap material. Further, using the conventional and inverted structure of the solar cell revels that inverted structure is the best performing among all the other structures with a highest Power Conversion Efficiency (PCE) of 2.08%. This efficiency is 1.6 times higher than the 0.78 % PCE achieved for the experimental solar cell. Thus, the findings of present work represent strategies for increasing the efficiencies and can be extremely useful for the design and development of high efficiency solar cells. This work additionally addresses the necessity for non-invasive biomedical sensing technology, particularly for haemoglobin detection. A low-cost, portable haemoglobin detector device is proposed, using organic solar cells and LED light sources. The device uses haemoglobin’s optical absorption properties to assess blood haemoglobin levels in a non-invasive manner, providing a simple, biocompatible, and flexible method of screening populations for anaemia. Further, the present work showcased a non-invasive method of haemoglobin detection comprising of an organic photovoltaic cell and three LED’s sources i.e., blue, green and red. These are used with their respective radiation spectral range of 450-495 nm, 495-570 nm and 620-750 nm to illuminate an area of the skin on finger. This transmitted light after interacting with tissues is detected by an arrangement of Coumarin 30: C60/NN’-QA/ZnPc active layer based organic solar cell. vi The Coumarin 30: C60/NN’-QA/ZnPc based multilayer organic photovoltaic solar cell is made up of three organic photodetector layers individually sensitive towards the blue, green, and red colour lights, which are arranged in a stack one above the other. The proposed multilayer photovoltaic cell has shown an excellent selectivity of the spectrum and also demonstrated separation of the colours in the photovoltaic cell. This excellent capability to separate the colours makes this organic photovoltaic cell to further utilise as a photodetector to realise a haemoglobin detector device by combining it with blue, green, and red colour LEDs. The photodetector detects the haemoglobin present in RBC owing to the optical property of haemoglobin not to absorb or to reflect the red colour. This transmitted red colour wavelengths are absorbed by the ZnPc layer of the multilayer structure producing a photosensitivity of 0.02 A/W. Thus, the method used in this work presents a simple, low-cost, non-invasive, biocompatible, and flexible means for assessing blood haemoglobin level by utilizing an multi spectral optical processing method. The method developed herein can further integrate to wearable electronic devices. This method will be extremely useful for checking anaemia anywhere and will be vital primarily for children and women suspected to be anaemic. Furthermore, the incorporation of solar cells into biomedical implants is explored, especially for powering cardiac pacemakers. Current pacemakers rely on batteries that must be replaced surgically, posing risks and complications. The work explores the feasibility of powering a modern cardiac pacemaker with a subdermal PPV-PCBM bulk heterojunction organic photovoltaic cell. Power yield analyses are performed for different skin tones and implantation depths. Thus, in the present work, subdermal PPV–PCBM [poly(2-methoxy-5-{3′,7′- dimethyloctyloxy}-p-phenylene vinylene) and {6,6}-phenyl C61-butyric acid methyl ester] active layer-based bulk heterojunction (BHJ) organic photovoltaic cell is analysed to power a modern pacemaker. A power output of 2.1 mW, 0.45 mW and 0.05 mW for Caucasian, Asian and African skin types is obtained at 2 mm implantation depth, respectively, which is adequate to run modern pacemakers requiring power in the range of (~10) microwatts. Further, the results also specifically show that the higher output power is produced under brighter and thinner skin. The photovoltaic cell used in this work allows for sufficient energy harvesting to electrically charge an energy storing accumulator in six (6) minutes when exposed to daylight. This energy vii accumulator can run a medical pacemaker for a total of twenty-four (24) hours. This analysis shows promising results and thus applicability of sub-dermal PV device for powering cardiac pacemaker. The sub-dermally implanted organic PV cell could increases the lifespan of cardiac pacemaker therefore, dropping the number of complex surgeries essential for replacement of the implants. Subsequently, this has also reduced the size of bio-medical implant and thus increasing the comfort level of patients. Additionally, such organic photovoltaic cell can be used to power up other bio-medical similar types of implants. In summary, this work contributes to the advancements in solar cell technology for biomedical applications and energy harvesting. The findings demonstrate that Sb and Sn doped ZnTe thin films have the potential to increase solar cell efficiency. The organic solar cell integration into biomedical devices opened the possibilities for non-invasive diagnostics and self-powered implants. The findings emphasise the need of optimising absorber layer materials and device designs to improve solar cell performance. Furthermore, the utilisation of organic solar cells in biomedical applications has the potential to transform healthcare technology that too with contributing to sustainable energy solutions.