Study On The Optics And Carrier Dynamics Of Nanostructured Photovoltaic Devices

Nanostructured photovoltaic devices have attracted tremendous attention in recent years due to the possibility of well controlling the light-device interaction for much improved light-trapping and photoconversion efficiency.Nanophotonic designs have been proved to be effective in enhancing the optical absorption,however do not certainly lead to a high electrical output due to the restriction of electrical losses under a variety of semiconductor mechanisms.This paper reports a comprehensive analysis of photovoltaic loss and puts forward a variety of device optimization design.With the emergence of new materials and new strucutres,nanostructured photovoltaic devices are increasingly susceptible to a variety of physical mechanisms.In addition to the typical photoelectric response,nanostructured photovoltaic devices also have strong temperature and heat dependence.Therefore,only delving into the inherent mechanisms from optical,electrical and thermodynamic aspects,can we understand the essences of energy conversion and conservation of photovoltaic devices.Based on the optoelectronic simulation technology of solar cell,a more perfect and universal three-dimensional opto-electro-thermal simulation system is constructed.The optical,electrical and thermal problems in the photovoltaic device are successfully integrated,and can be simultaneously simulated in both frequency domain and space domain.Based on this technique,several advanced designs for high-efficiency photovoltaic devices are obtained.The core research achievements of this thesis are listed as follows:(1)Surface plasmons polartions(SPPs)for photovoltaic applications are the hot topics of the past few years.However,the study of optical reponses based on nanophotonics is more common,which is difficult to accurately reflect the true optoelectronic conversion performance of the device.In particular,with the introduction of complex metal layers,the semiconductor-to-metal interface recombination significantly restrains performance improvement.In this paper,the rigorous optoelectronic simulation of SPPs solar cells(SPSCs)is realized,and the gallium arsenide(GaAs)solar cells are taken as an example to study the optical enhancement and electrical recombination in the process of introducing SPPs.The results show that the local field effect of SPPs can greatly enhance the light absorption,but also increases the carrier recombination of the device,which suppresses the improvement of electrical performance of the device.Based on the optoelectronic simulation technology,the paper puts forward that the space separation of the photogenerated carriers and the recombination surface can be realized by combining plasmonic design with electrical window layer,which greatly suppresses the surface recombination and improves the overall optoelectronic conversion performance of the device.This work provides a platform and design idea for the design and development of SPSCs with high optoelectronic conversion capability.(2)Nanowires and nanoholes solar cells are favored by their excellent optical properties.However,due to the large surface area-volume ratio,the photocurrent loss arising from surface recombination is serious.By taking into account the optical and electrical responses of three-dimensional nanostructured photovoltaic devices,a comprehensive optoelectronic simulation of the device is carried out,and the device is optimized based on the simulation results.Studies show that geometrically identical nanowire cells with radial doping have better electrical performance than axially doped cells.By using radial electrical doping profiles,the photogenerated carriers can be quickly separated and the surface recombination of the device can be much reduced.This work provides a reference for the design of the overall performance of three-dimensional nanostructured photovoltaic devices.(3)For a long time,the study of photovoltaic devices mostly focuses on how to enhance light absorption and improve optoelectronic conversion efficiency,while rarely look deep into the internal loss mechanisms of solar cell.In this paper,from the perspectives of the current,voltage and energy,we conduct a comprehensive study of the transmission and reflection loss,surface recombination,bulk recombination,carrier heat,Joule heat and Peltier effect on the performance of solar cell.We comprehensively study spectral response and spatial distribution of different forms of loss.The results show that the surface recombination and the bulk recombination cause the current loss,and the thermalization and Joule heat are the most important heat generation mechanism of the device.The Peltier effect limits the open circuit voltage of the solar cell.This quantitative analysis of the method for the in-depth study of the solar cell is benificial to master the device loss mechanism,regulate and suppress of specific losses,and achieve efficient and low cost design.(4)With the wide application of new material and new structure in photovoltaic devices,the physical mechanisms of micro-nano photovoltaic devices have become very complex.Optical,electrical and thermodynamic characteristics become inseparable factors in solar cells.Therefore,the combination of photoelectric characteristics of multi-physics coupling simulation technology is of great significance to explore the photovoltaic device and accurately predicte of device performance,design and control of high conversion efficiency device.In view of this,this paper constructs a fully coupled opto-electro-thermal simulation system,and studies the response of optical,electrical and thermodynamics of nanostructured photovoltaic devices in frequency and spatial domains.Through the strong coupling analysis of optics,electric and thermodynamics,the physical losses in the device are quantified,and the thermal effect as well as temperature distribution in the device is predicted.The realization of opto-electro-thermal simulation plays a crucial role in designing the photovoltaic devices.