Browsing by Author "Charlton, Martin"

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Characteristics of Conductive Polymer/Silicon Heterojunction Solar Cells with Periodic Nanostructures
(2013)
Huang, Yang-Yue
;
Pan, Ward
;
Lai, Yi-Chun
;
Yang, T. T.
;
Chen, Riqui
Mono- and multi-crystalline silicon photovoltaics currently still hold more than 80% market share because of the non-toxic, abundant material resources used, and their long-term stabilities. However, the cost of solar power is still more than three times that of fossil fuels, which necessitates a further reduction to accelerate its widespread use. It has been estimated that cell fabrication consumes 30% of the total manufacturing cost due to energy intensive semiconductor processes, such as high temperature furnace for doping, electrodes co-firing, high-vacuum chemical deposition, etc. Therefore, the organic-inorganic hybrid cell concept has been proposed to take advantage of the solution-based processes for rapid and low-cost production and the wide absorption spectrum of silicon. In this work, we demonstrate a hybrid heterojunction solar cell based on the structure of conductive polymer PEDOT:PSS spun cast on n-type crystalline silicon nanorod (SiNR) arrays with periodic arrangements. The nanorod arrays are fabricated by electron beam (E-beam) lithography followed by reactive-ion etching (RIE), which show capability to enhance light harvesting. In addition, SiNRs and PEDOT:PSS can form core-shell structure that provides a large p-n junction area for carrier separation and collection. We measured the optical and photovoltaic characteristics of these devices under a simulated class A solar simulator with a calibrated illumination intensity of 1000 W/m(2) for the AM1.5G solar spectrum. A post-RIE damage removal etching (DRE) is subsequently introduced in order to mitigate the surface recombination issues and also alter the surface reflection due to modifications in the nanorod side-wall profile. Finally, we show that the DRE treatment can effectively recover the carrier lifetime and dark current-voltage characteristics of SiNRs hybrid solar cells to resemble the planar counterpart without RIE damages.
Impact of Light Management on Photovoltaic Characteristics of GaAs Solar Cells with Photonic Crystals and Quasi-Photonic Crystals
(2014)
Lai, Yi-Chun
;
Yang, Tung-Ting
;
Yu, Peichen
;
Hung, Mu-Min
;
Charlton, Martin
In detailed balance model, the efficiency of single-junction solar cells can be potentially as high as 33.5% under AM 1.5G illumination. However the best state-of-the-art devices are still far lower than those figures, even the electronic quality is nearly perfect. Therefore the efficiency gap should stem from the light management inside solar cells. Recently, external radiation efficiency (eta ext) derived from detailed balance model is emphasized to evaluate light management and photon recycling, which aggregates the loss of backward emission into substrate and non-radiative recombination. This factor can be highly relevant to the cell\'s performance, especially open-circuit voltage (Voc), and maximizing Voc is generally considered as the last mile to approach ultra-high efficiency limit. In this work, we try to quantify the Voc enhancement in GaAs solar cells by enhancing light extraction. The simulation tools are RCWA simulation and photon recycling model NREL developed recently. The top structures we simulate here are TiO2 cones arranged in three PC/QPC lattices. After our calculation, the QPC 12-folds symmetry can make the biggest Voc enhancement 11.21meV compared with bare one, and the structure also possess extraordinary omni-directional anti-reflection ability for maintaining high Jsc. Our results also show that using this way to enhance Voc is especially suitable for cells with ordinary material quality. Therefore, the requests of ideal top structures for solar cells\' use are not only near-perfect anti-reflection, but the ability to maximize light extraction if no feature of angular filter exists.