Strategies to achieve 15% efficiency hybrid organic-silicon heterojunction solar cells
| Autor: | Lai, Yi-Chun, 賴逸群 |
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| Rok vydání: | 2018 |
| Druh dokumentu: | 學位論文 ; thesis |
| Popis: | 106 According to the report of Greentech Media (GTM) research in America, 59 gigawatts of solar Photovoltaics (PV) were installed globally in 2015, a 34 percent increase over 2014’s total, the total installed solar PV reached 256 gigawatts. GTM Research expected global PV demand between 2015 and 2020 will be increased by an average of 10 percent to 15 percent annually and the cumulative worldwide PV installation to reach 754 gigawatts in 2020. Moreover, U.S. Utility-scale solar photovoltaic power produced more than 9.5 gigawatts in 2016, which exceeded the capacity of natural gas, making PV the most dominant new fuel source for the first time, according to the U.S. Energy Information Administration (EIA). Wafer-based silicon photovoltaics currently dominate the solar cells industry around 80% of the market. However, the price of silicon photovoltaics needs to be further decreased to accelerate the wide-spread use. Therefore, in our research, we aim to lower the cost of silicon photovoltaics by using low-temperature, solution processes to realize high efficiency hybrid organic silicon heterojunction solar cells. In this thesis, we firstly etch the surface of silicon substrates to make nano-textures, and then spin-cast high conductive organic polymer (PEDOT:PSS) on silicon to form hybrid heterojunction solar cells. Due to the carrier recombination loss at the interface, we applied rear interfacial engineering on silicon via a soluble blade coating process. There, we dissolve organic small molecule powder, Alq3 and OXD-7 with methanol, and use an automatic blade-coating process to coat the organic thin film on the rear surface of silicon. By tuning the coating thickness with various coating speeds, we successfully achieve the best power conversion efficiency (PCE) of 11.89% for the Alq3 devices, and 12.90% for the OXD-7 devices. The characteristics of the hybrid solar cell devices with the two rear interlayers can be further explored through a capacitance-voltage (C-V) measurement, we found the molecular layers can effectively increase built-in potential which is helpful to separate carriers. Moreover, OXD-7 also permits the interlayer to function as a hole-blocking layer (HBL) which could increase the minority carrier lifetime and boost the open-circuit voltage for solar cells. Furthermore, highly transparent and conductive Carbon-nanotube (CNT) doped PEDOT:PSS is employed to realize the solution-processed hybrid silicon heterojunction solar cells. After optimization of depth of silicon nanowires and suitable work-function turning, the best PCE can reach 14.42%. To offset the sacrifice of shorter length nanowires, we deposit a 30 nm thick SiOx layer for antireflection layer and the efficiency can reach to 15.16%. In order to improve the carrier collection and conductivity of front contact, we apply transparent conductive graphene/PET on the planar silicon hybrid solar cells. The high quality graphene is grown by chemical vapor deposition (CVD), transferred to PET thin films, and then attached onto the front surface of device. With the help of two layers graphene, the efficiency of planar silicon hybrid solar cell achieves 8.95%, showing a 53% enhancement factor. Throughout these efforts, we have successfully demonstrated various low-temperature, solution process approaches in order to address the goals of high efficiency, low-cost hybrid organic silicon heterojunction solar cells. |
| Databáze: | Networked Digital Library of Theses & Dissertations |
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