Jheng-Jie Liu

Light-trapping performance of silicon thin-film plasmonics solar cells based on indium nanoparticles and various TiO2 space layer thicknesses

Thin-film solar cells have the potential to substantially reduce the material cost of photovoltaic devices. However, to increase the amount of light absorbed in the thin active layer, light trapping is a critical concern in developing thin-film solar cells. In this study, we investigated the suitability of using localized surface plasmons of indium nanoparticles (In NPs) on TiO2 space layers of various thicknesses to enhance the absorption of silicon (Si) thin-film solar cells. The experimental results demonstrated how the combined effects of the incident light plasmonics scattering, surface passivation, and antireflection of In NPs affect the photovoltaic performance of the TiO2 space layer. The optical reflectance, dark current, photocurrent, and external quantum efficiency were measured and compared. Compared with bare-type Si thin-film solar cells, the proposed cells with In NPs on a 59.5-nm-thick TiO2 space layer demonstrated a short-circuit current enhancement of 45.7% (from 2.56 to 3.73 mA) and a conversion efficiency enhancement of 36.2% (from 7.56 to 10.3%).

Photovoltaic Performance Characterization of Textured Silicon Solar Cells Using Luminescent Down-Shifting Eu-Doped Phosphor Particles of Various Dimensions

This paper reports on efforts to enhance the photovoltaic performance of textured silicon solar cells through the application of a layer of Eu-doped silicate phosphor with particles of various dimensions using the spin-on film technique. We examined the surface profile and dimensions of the Eu-doped phosphors in the silicate layer using optical microscopy with J-image software. Optical reflectance, photoluminescence, and external quantum efficiency were used to characterize the luminescent downshifting (LDS) and light scattering of the Eu-doped silicate phosphor layer. Current density-voltage curves under AM 1.5G simulation were used to confirm the contribution of LDS and light scattering produced by phosphor particles of various dimensions. Experiment results reveal that smaller phosphor particles have a more pronounced effect on LDS and a slight shading of incident light. The application of small Eu-doped phosphor particles increased the conversion efficiency by 9.2% (from 12.56% to 13.86%), far exceeding the 5.6% improvement (from 12.54% to 13.32%) achieved by applying a 250 nm layer of SiO2 and the 4.5% improvement (from 12.37% to 12.98%) observed in cells with large Eu-doped phosphor particles.

Photocurrent of MOS-Si photovoltaic device enhanced by an auxiliary biasing solar cell

We demonstrate a novel concept for a MOS-structure Si photovoltaic device with an increasing in photocurrent of 12.93% based on a biasing source applied to the MOS transparent ITO-gate-electrode using an auxiliary biasing solar cell.

Enhancing Photovoltaic Performance Using Broadband Luminescent Down-Shifting by Combining Multiple Species of Eu-Doped Silicate Phosphors

This paper demonstrates the application of a broadband luminescent downshifting (LDS) layer with multiple species of europium (Eu)-doped silicate phosphors using spin-on film technique to enhance the photovoltaic efficiency of crystalline silicon solar cells. The surface morphology of the deposited layer was examined using a scanning electron microscope (SEM). The chemical composition of the Eu-doped silicate phosphors was analyzed using energy-dispersive X-ray spectroscopy (EDS). The fluorescence emission of the Eu-doped silicate phosphors was characterized using photoluminescence (PL) measurements at room temperature. We also compared the optical reflectance and external quantum efficiency (EQE) response of cells with combinations of various Eu-doped phosphors species. The cell coated with two species of Eu-doped phosphors achieved a conversion efficiency enhancement (∆η) of 19.39%, far exceeding the ∆η = 15.08% of the cell with one species of Eu-doped phosphors and the ∆η = 8.51% of the reference cell with the same silicate layer without Eu-doped phosphors.

Electrical and Optical Characterization of Sputtered Silicon Dioxide, Indium Tin Oxide, and Silicon Dioxide/Indium Tin Oxide Antireflection Coating on Single-Junction GaAs Solar Cells

This study characterized the electrical and optical properties of single-junction GaAs solar cells coated with antireflective layers of silicon dioxide (SiO2), indium tin oxide (ITO), and a hybrid layer of SiO2/ITO applied using Radio frequency (RF) sputtering. The conductivity and transparency of the ITO film were characterized prior to application on GaAs cells. Reverse saturation-current and ideality factor were used to evaluate the passivation performance of the various coatings on GaAs solar cells. Optical reflectance and external quantum efficiency response were used to evaluate the antireflective performance of the coatings. Photovoltaic current-voltage measurements were used to confirm the efficiency enhancement obtained by the presence of the anti-reflective coatings. The conversion efficiency of the GaAs cells with an ITO antireflective coating (23.52%) exceeded that of cells with a SiO2 antireflective coating (21.92%). Due to lower series resistance and higher short-circuit current-density, the carrier collection of the GaAs cell with ITO coating exceeded that of the cell with a SiO2/ITO coating.

Fabrication and performance characterization of 1550 nm hetero-multiplication avalanche photodiodes for single photons detection

We report the fabrication and performance characterization of 1550 nm separate absorption, grading, charge, and InP/InAlAs hetro-multiplication avalanche photodiodes (SAGCHM APDs) for single photon detection applications. The linear mode performance of the fabricated APDs are firstly characterized that the dark current at 95% of the breakdown voltage was 30 pA and 15 nA at 200K and 300K, respectively. The gain-bandwidth product of 62 GHz was obtained at room temperature. For single photons detection characterization, however, our APD was operated in the gated passive quenching mode, at lower temperature and incorporated with an optimizing spike-cancellation self-differencing circuit. Under the temperature of -50°C and the gate repetition frequency of 100 KHz with pulse width of 2 ns, the lowest dark count probability (Pdc) of 1.2 x 10-5, the highest single-photon detection efficiency (ηdet) of 22.5%, and the lowest noise equivalent power (NEP) of 1.5x10-15 W/(Hz)1/2 were obtained, respectively. Moreover, we demonstrated the transmission distance as a function of quantum bit error rate (QBER) based on the obtained performance parameters. The maximum transmission distance, at QBER=15%, of 43 km was achieved.

Fabrication and Characterization of Planar-Type Top-Illuminated InP-Based Avalanche Photodetector on Conductive Substrate with Operating Speeds Exceeding 10 Gbps

This paper presents a high-speed top-illuminated InP-based avalanche photodetector (APD) fabricated on conductive InP-wafer using planar processes. The proposed device was then evaluated in terms of DC and dynamic performance characteristics. The design is based on a separate absorption, grading, charge, and multiplication (SAGCM) epitaxial-structure. An electric field-profile of the SAGCM layers was derived from the epitaxial structure. The punch-through voltage of the SAGCM APD was controlled to within 16–17 V, whereas the breakdown voltage (VBR) was controlled to within 28–29 V. We obtained dark current of 2.99 nA, capacitance of 0.226 pF, and multiplication gain of 12, when the APD was biased at 0.9 VBR at room temperature. The frequency-response was characterized by comparing the calculated 3-dB cut-off modulation-frequency (f3-dB) and f3-dB values measured under various multiplication gains and modulated incident powers. The time-response of the APD was evaluated by deriving eye-diagrams at 0.9 VBR using pseudorandom non-return to zero codes with a length of 231-1 at 10–12.5 Gbps. There was a notable absence of intersymbol-interference, and the signals remained error-free at data-rates of up to 12.5 Gbps. The correlation between the rise-time and modulated-bandwidth demonstrate the suitability of the proposed SAGCM-APD chip for applications involving an optical-receiver at data-rates of >10 Gbps.

Photovoltaic Performance Enhancement of Silicon Solar Cells Based on Combined Ratios of Three Species of Europium-Doped Phosphors

This paper presents a scheme for the enhancement of silicon solar cells in terms of luminescent emission band and photovoltaic performance. The proposed devices are coated with an luminescent down-shifting (LDS) layer comprising three species of europium (Eu)-doped phosphors mixed within a silicate film (SiO2) using a spin-on film deposition. The three species of phosphor were mixed at ratios of 0.5:1:1.5, 1:1:1, or 1.5:1:0.5 in weight percentage (wt %). The total quantity of Eu-doped phosphors in the silicate solution was fixed at 3 wt %. The emission wavelengths of the Eu-doped phosphors were as follows: 518 nm (specie-A), 551 nm (specie-B), and 609 nm (specie-C). We examined the extended luminescent emission bands via photoluminescence measurements at room temperature. Closely matching the luminescent emission band to the high responsivity band of the silicon semiconductor resulted in good photovoltaic performance. Impressive improvements in efficiency were observed in all three samples: 0.5:1:1.5 (20.43%), 1:1:1 (19.67%), 1.5:1:0.5 (16.81%), compared to the control with a layer of pure SiO2 (13.80%).

Electrical and optical characterization of thermally deposited indium-tin-oxide film on high efficiency single-junction GaAs solar cell

The thermally deposited indium-tin-oxide (ITO) film on single-junction GaAs solar-cell as an excellent antireflection, passivation and window layer to achieve higher efficiency is demonstrated. The passivated characteristic of the ITO-film on GaAs solar-cell is examined by saturation-current and ideality factor. The antireflection of the ITO-film on GaAs solar-cell is revealed by optical-reflectance and external quantum-efficiency. The efficiency of 23.52% for the GaAs cell with ITO antireflection-coating (ARC) was higher than that of 21.92% for the GaAs cell with SiO2 ARC.

Light trapping of plasmonics textured silicon solar cells based on broadband light scattering and wide acceptance angle of indium nanoparticles

In this study, light trapping of textured silicon solar cell based on light scattering and angle of incident light of plasmonics indium nanoparticles (In NPs) of various dimensions is demonstrated. The light trapping modes of textured surface with and without In NPs for incident angles of 0°, 35.3°, and 54.7° are proposed and characterized. The optical reflectance, external quantum efficiency and photovoltaic performance depended on the dimensions of plasmonics In NPs and angles of incident light are measured and compared.