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Perovskite solar cells exhibit outstanding device performance and photovoltaic potential in recent ten years. However, the photoactive layer of the majority of perovskite solar cells with outstanding efficiency currently contains toxic lead. Although perovskite solar cells will be encapsulated prior to application to enhance the device's stability and prevent lead leakage, it is still possible for the devices to be broken or exposed to the environment during actual use. Correspondingly, Pb may enter water or soil through rainfall, posing health risks to humans and other creatures. To prepare perovskite solar cell devices with both high performance and low toxicity, current research concentrates primarily on Pb-Sn hybrid perovskite solar cells as Sn is less toxic than Pb from an environmental standpoint. To intuitively compare the lead leakage of Pb-based perovskite solar cells and Pb-Sn hybrid perovskite solar cells, this study simulated the lead leakage scenario under heavy rainfall conditions using self-prepared, good-performance solar cell devices. Our results indicate that Pb-Sn hybrid perovskite solar cells have less lead leakage than Pb-based perovskite solar cells. The lead leakage concentration of Pb-Sn hybrid perovskite solar cells was 36.8% (in the dripping test) and 41.2% (in the soaking test) lower than that of Pb-based perovskite solar cells.

京都大学 / 新制・課程博士 / 博士(理学) / 甲第24443号 / 理博第4942号 / 新制||理||1706(附属図書館) / 京都大学大学院理学研究科化学専攻 / (主査)教授 若宮 淳志, 教授 依光 英樹, 教授 畠山 琢次 / 学位規則第4条第1項該当 / Doctor of Science / Kyoto University / DGAM

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The development of devices with high efficiencies can only be attained by tandem structures which are important to the advancement of thin-film photoelectrochemical (PEC) and photovoltaic (PV) technologies. FSEC PV Materials Lab has developed a PEC cell using multiple bandgap tandem of thin film PV cells and a photocatalyst for hydrogen production by water splitting. CdS/CdTe solar cell, a promising candidate for low-cost, thin-film PV cell is used as one of the thin film solar cells in a PEC cell. This research work focuses on developing various back contacts with good transparency in the infrared region (~750 - 1150 nm) for a CdS/CdTe solar cell. CdS/CdTe solar cells were prepared with three different configurations, Glass/SnO2:F/CdS/CdTe/ZnTe:Cu/ITO/Ni-Al (series 1), Glass/SnO2:F/CdS/CdTe/Cu2Te/ITO/Ni-Al (series 2), Glass/SnO2:F/CdS/CdTe/Br-Me etching/Cu/ITO/Ni-Al (series 3). The back contact preparation process for a CdS/CdTe solar cell involves the deposition of a primary p-type back contact interface layer followed by the deposition of transparent and conducting ITO and a Ni-Al outer metallization layer. Back contact interface layers were initially optimized on glass substrates. A ZnTe:Cu layer for a series 1 cell was deposited using hot wall vacuum evaporation (HWVE). Cu2Te and Cu thin films for series 2 and series 3 cells were deposited by vacuum evaporation. HWVE technique produced highly stoichiometric ZnTe:Cu thin films with cubic phase having {111} texture orientation. All the back contact interface layers demonstrated better transparency in the infrared region on glass substrate. Formation of crystalline phase and texture orientation were studied using X-ray diffraction (XRD). The composition was analyzed by electron probe microanalysis (EPMA). Transparency measurements were carried out by optical transmission spectroscopy. Thickness measurements were carried out using a DEKTAK surface profile measuring system. Finally, completed solar cells for all the series were characterized for current-voltage (I-V) measurements using the I-V measurement setup developed at the FSEC PV Materials Lab. The PV parameters for the best series 1 cell measured at an irradiance of 1000 W/m2 were: open circuit voltage, Voc = 630 mV, short circuit current, Isc = 7.68 mA/ cm2, fill factor, FF = 37.91 %, efficiency, ç = 3.06 %. The PV parameters for the best series 2 cell measured were: Voc = 690 mV, Isc = 8.7 mA/ cm2, FF = 45.19 %, ç = 4.8 %. The PV parameters for the best series 3 cell measured were: Voc = 550 mV, Isc = 9.70 mA/ cm2, FF = 42.25 %, ç = 5.63 %. The loss in efficiency was attributed to the possible formation of a non-ohmic contact at the interface of CdTe and back contact interface layer. Decrease in the fill factor was attributed to high series resistance in the device.

This thesis introduces the design and analysis of a single-stage inverter. A circuit was designed and simulated as a proof of concept to investigate the possibility of using boost and buck-boost converters to provide an AC output. The proposed circuit utilizes non-synchronous boost and buck-boost converters due to their simplicity in control signals as opposed to synchronous converters. The application of the proposed inverter is for use with individual solar cells. The aim of the inverter for a single cell is to improve the efficiency of a solar panel, whose performance is limited to the performance of the least efficient cell. With each cell independent of any other cell in the solar panel, the overall efficiency of the panel can be improved. This circuit uses a 3.6VDC input from the solar cell to produce a 10VPP 60Hz square wave output. The inverter consists of a solar cell, two DC-DC converters, two linear dropout (LDO) regulators, a square wave generator, and a switching circuit . The design and analysis of all parts were investigated individually in detail. The different parts of the circuit were then simulated using LTspice before testing the overall circuit. Simulation results demonstrate the feasibility of the proposed inverter with all design requirements but efficiency meeting or exceeding the goals.

An LED-based solar simulator has been designed, constructed, and qualified under ASTM standards for use in the Cal Poly Space Environments Laboratory. The availability of this simulator will enhance the capability of undergraduate students to evaluate solar cell and thermal coating performance, and offers further research opportunities. The requirements of ASTM E927-19 for solar simulators intended for photovoltaic cell testing were used primarily, supplemented by information from ASTM E491-73 for solar simulators intended for spacecraft thermal vacuum testing. Three main criteria were identified as design goals - spectral match ratio, spatial non-uniformity, and temporal instability. An electrical design for an LED-based simulator to satisfy these criteria was developed and implemented, making use of existing lab equipment where possible to minimize cost. The resulting simulator meets the desired spatial non-uniformity and temporal instability requirements of ASTM E927-19, but falls short of the spectral match ratio needed. This is shown to be due to a calibration issue that is easily amended via software. The simulator is overall Class UCB under ASTM E927, and Class CCC under ASTM E491. The simulator was used to conduct the same laboratory procedure for solar cell I-V curve testing as performed by undergraduate students, showing excellent promise as a course enhancement.

Research to increase the efficiency of conventional solar cells is constantly underway. The goal of this work is to increase the efficiency of conventional solar cells by incorporating quantum dot (QD) nanoparticles in the absorption mechanism. The strategy is to have the QDs absorb UV and fluoresce photons in the visible region that are more readily absorbed by the cells. The outcome is that the cells have more visible photons to absorb and have increased power output. The QDs, having a CdSe core and a ZnS shell, were applied to the solar cells as follows. First, the QDs were synthesized in an octadecene solution, then they were removed from the solution and finally they were dried and deposited into polydimethylsiloxane (PDMS) and the PDMS/QD composite is allowed to cure. The cured sample is applied to a silicon solar panel. The panel with the PDMS/QD application outputs 2.5% more power than the one without, under identical illumination by a tungsten halogen lamp, using QDs that fluoresce in the orange region. This work demonstrates the feasibility of incorporating QDs to increase the efficiency of conventional solar cells. Because the solar cells absorb better in the red region, future effort will be to use QDs that fluoresce in that region to further boost cell output.

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Renewable and clean energy is urgently needed to cope with the climate crisis. Photovoltaics (PV) has been the fastest growing technology in the clean energy market due to its low cost, and the abundance of solar energy. The capacity of silicon-based PV is rapidly expanding with evolving technologies. Passivating the solar cell’s electrical contacts is a widely accepted strategy for the PV industry to improve device power conversion efficiency (PCE). Polycrystalline silicon (Poly-Si) passivating contacts are one of the promising concepts in the emerging class of passivating contacts. In this dissertation, the passivation mechanism of Poly-Si passivating contacts is investigated. Moreover, the influence of dopant diffusion on the passivation quality is revealed. To address the side-effects of dopant diffusion, a thin buffer layer is inserted between the Poly-Si(p) layer and the $SiO_x$ layer. With such a buffer layer, the passivation of the Poly-Si passivating contact is improved, which in turn, enhances the device PCE. In addition to passivating contacts, this dissertation also explores carrier-selective contact of crystalline silicon (c-Si) and low work function metal – Li. Li is a very reactive metal which makes the fabrication process a challenge. To overcome such a challenge, the c-Si/ Li contact is fabricated by thermally decomposing stable $Li_3N$ powder instead of metal evaporation. The c-Si/Li contact shows an excellent electron-selective transport performance with a 0.39 eV energy barrier. Full-area Si/Li rear contact devices are fabricated, and >19% PCE and >80% fill factor are achieved. To accelerate the device optimization, a physical model embedded machine-learning approach is applied to transparent conductive oxide (TCO) materials optimization. In this work, empirical correlations between sputtering parameters and the deposited TCOs’ electrical properties are established. Then a Bayesian Parameter Estimation (BPE) algorithm is applied to learn the empirical model. With this BPE network, the TCOs’ electrical properties are successfully predicted with limited material characterizations. Thanks to the combination of BPE and a physical model network, the material optimization process is significantly accelerated. In summary, this dissertation explores different aspects to develop novel passivating and carrier-selective contacts for c-Si solar cells, and introduces an approach to accelerate the development processes.