Song-Yeu Tsai

Investigation of Low-Cost Surface Processing Techniques for Large-Size Multicrystalline Silicon Solar Cells

The subject of the present work is to develop a simple and effective method of enhancing conversion efficiency in large-size solar cells using multicrystalline silicon (mc-Si) wafer. In this work, industrial-type mc-Si solar cells with area of 125×125 mm2 were acid etched to produce simultaneously POCl3 emitters and silicon nitride deposition by plasma-enhanced chemical vapor deposited (PECVD). The study of surface morphology and reflectivity of different mc-Si etched surfaces has also been discussed in this research. Using our optimal acid etching solution ratio, we are able to fabricate mc-Si solar cells of 16.34% conversion efficiency with double layers silicon nitride (Si3N4) coating. From our experiment, we find that depositing double layers silicon nitride coating on mc-Si solar cells can get the optimal performance parameters. Open circuit (Voc) is 616 mV, short circuit current (Jsc) is 34.1 mA/cm2, and minority carrier diffusion length is 474.16 μm. The isotropic texturing and silicon nitride layers coating approach contribute to lowering cost and achieving high efficiency in mass production.

Efficiency Improved by Forming Gas Treatment for Si-Based Solar Cell Applications

The photovoltaic (PV) effects have been investigated and improved using efficient treatments both on single-crystalline (sc) and on multicrystalline (mc) silicon (Si) solar cells. The major effect of forming gas (FG) treatment on solar cell performance is the fill-factor values, which increase 3.75% and 8.28%, respectively, on sc-Si and mc-Si solar cells. As for the optimal 15%- ratio and 40-minute FG treatment, the conversion efficiency () values drastically increase to 14.89% and 14.31%, respectively, for sc- and mc-Si solar cells. Moreover, we can measure the internal quantum efficiency (IQE) values increase with -FG treatment under visible wavelength (400~900 nm) radiation. Thus based on the work in this research, we confirm that passivation has become crucial both in PV as well as in microelectronics fields. Moreover, the developed mc-Si solar cell by proper FG treatment is quite suitable for commercial applications.

Performance Improvements of Selective Emitters by Laser Openings on Large-Area Multicrystalline Si Solar Cells

This study focuses on the laser opening technique used to form a selective emitter (SE) structure on multicrystalline silicon (mc-Si). This technique can be used in the large-area (156 × 156 mm2) solar cells. SE process of this investigation was performed using 3 samples SE1–SE3. Laser fluences can vary in range of 2–5 J/cm2. The optimal conversion efficiency of 15.95% is obtained with the SE3 (2 J/cm2 fluence) after laser opening with optimization of heavy and light dopant, which yields a gain of compared with that of a reference cell (without fluence). In addition, this optimal SE3 cell displays improved characteristics compared with other cells with a higher average value of external quantum efficiency ( = 68.6%) and a lower average value of power loss ( = 2.33 mW/cm2). For the fabrication of solar cells, the laser opening process comprises fewer steps than traditional photolithography does. Furthermore, the laser opening process decreases consumption of chemical materials; therefore, the laser opening process decreases both time and cost. Therefore, SE process is simple, cheap, and suitable for commercialization. Moreover, the prominent features of the process render it effective means to promote overall performance in the photovoltaic industry.

Flexible and Cd free CIGS solar cell yielding 13.37% efficiency producing by non-vacuum process

CIGS solar cell has yielded the high efficiency beyond 20% on glass substrate [1], but some drawbacks such as heavy, not portable, toxic and costly need to be met for future manufacture. In this study, ZnS(O,OH)/CIGSeS solar cells were fabricated on flexible stainless steel substrate by low-cost nano-particle printing process. The flexible and non-toxic CIGSeS solar cell shows the efficiency as high as 13.37% without anti-reflection layer. The high efficiency was attributed to good thin film quality in absorption layer and buffer layer. Besides, the ZnS(O,OH) buffer layer with thickness only 15 nm shows good coverage, which enhances photocurrent and leads to high efficiency. Moreover, the CIGSeS solar cells were placed to dark room for 3 days to test light soaking effects, the results show that only 0.14% efficiency decay was measured. The results implies that the non-toxic and flexible CIGSeS solar cells prepared by nanoparticle printing process shows high potential for portable power source and building integrated photovoltaic system.

CdS thin film prepared by shallow chemical bath deposition for low cost CIGS thin film solar cell

It was well-known that the n-type buffer layer grown by the chemical bath deposition (CBD) technique showed the highest efficiency for CIGS thin film solar cell. However, CBD process showed a serious drawback of producing considerable of waste solution and low yield. In this study, a novel technique called shallow chemical bath deposition (SCBD) was employed to grown Cadmium sulfide (CdS) thin film. UV-visible-NIR spectrophotometer and scanning electronic microscopy were employed to characterized the thin film quality. The results hinted that the SCBD technique showed excellent potential to get high quality thin film, which could be suitable to mass production of buffer layer for CIGS thin film solar cells.

Effects of Sheet Resistance on mc-Si Selective Emitter Solar Cells Using Laser Opening and One-Step Diffusion

In order to simplify process procedure and improve conversion efficiency (η), we present new steps of laser opening and one-step POCl3 diffusion to fabricate selective emitter (SE) solar cells, in which heavily doped regions (HDR) and lightly doped regions (LDR) were formed simultaneously. For HDR, we divided six cells into two groups for POCl3 diffusion with sheet resistance () of 40 Ω/sq (for group A) and 50 Ω/sq (for group B). The dry oxidation duration at a temperature of 850°C was 18, 25, and 35 min for the 3 different cells in each group. This created six SE samples with different pairings for the HDR and LDR. The optimal cell (sample SE2) with values of 40/81 Ω/Sq in HDR/LDR showed the best η of 16.20%, open circuit voltage () of 612.52 mV, and fill factor (FF) of 75.83%. The improvement ratios are 1.57% for η and 14.32% for external quantum efficiency (EQE) as compared with those of the two-step diffusion process of our previous study. Moreover, the one-step laser opening process and omitting the step of removing the damage caused by laser ablation especially reduce chemistry pollution, thus showing ecofriendly process for use in industrial-scale production.