This paper shows that rapidly formed emitters in less than 6min in the hot zone of a conveyor belt furnace or in 3min in an rapid thermal processing (RTP) system, in conjunction with a screen-printed (SP) RTP Al-BSF and passivating oxide formed simultaneously in 2min can produce very simple high-efficiency n+-p-p+ cells with no surface texturing, point contacts, or selective emitter. It is shown for the first time that an 80Ω/□ emitter and SP Al-back surface field (BSF) formed in a high throughput belt furnace produced 19% FZ cells and greater than 17% CZ cells with photolithography (PL) contacts. Using PL contacts, we also achieved 19% efficient cells on FZ, >18% on MCZ, and ∼17% boron-doped CZ by emitter and SP Al-BSF formation in <10min in a single wafer RTP system. Finally, manufacturable cells with 45Ω/□ emitter and SP Al-BSF and Ag contacts formed in the conveyor belt furnace gave 17% efficient cells on FZ silicon. Compared to the PL cells, the SP cell gave ∼2% lower efficiency along with a decrease in Jsc and fill factor. This loss in performance is attributed to a combination of the poor blue response, higher series resistance and higher contact shading in the SP devices

The DOE Photovoltaic Manufacturing Technology (PVMaT) Project has conducted cost-shared manufacturing R&D with the photovoltaic industry for over 10 years. During, this time, research has focused on the project's stated objectives of improving photovoltaic manufacturing processes and products, lowering manufacturing costs, and providing a foundation for the scale-up of U.S. photovoltaic (PV) manufacturing. Progress made by each of the U.S. PV industry participants in this project has resulted in a significant reduction in the industry's direct PV module-manufacturing costs and an impressive scale-up in U.S. PV manufacturing capacity. The majority of the efforts have been module related. Results in terms of automation, yield, and throughput have provided a significant reduction in direct manufacturing costs. Cost reductions and capacity increases resulting from these efforts are discussed.

The US photovoltaic (PV) industry has made significant technical advances in crystalline silicon (Si) module manufacturing through the PV Manufacturing R&D Project during the past decade. Funded Si technologies in this project have been Czochralski, cast polycrystalline, edge-defined film fed growth (EFG) ribbon, string ribbon, and Si-film. Specific R&D Si module-manufacturing categories that have shown technical growth and are discussed are in crystal growth and processing, wafering, cell fabrication, and module manufacturing. These R&D advancements since 1992 have contributed to a 30% decrease in PV manufacturing costs and stimulated a sevenfold increase in PV production capacity.

A technique is presented to simultaneously diffuse boron and phosphorus in silicon, and grow an in-situ passivating oxide in a single furnace step. It is shown that limited solid doping sources made from P and B spin-on-dopant (SOD) films can produce optimal n/sup +/ and p/sup +/ profiles simultaneously without the deleterious effects of cross doping. A high quality passivating oxide is grown in-situ beneath the thin (/spl sim/60 /spl Aring/) diffusion glass, resulting in low J/sub 0/ values below 100 fA/cm/sup 2/ for transparent (/spl sim/100 /spl Omega///spl square/) phosphorus and boron diffusions. For the first time it is shown that impurities present in the boron SOD film can be effectively filtered out by employing separate source wafers, resulting in bulk lifetimes in excess of 1 ms for the sample wafers. The degree of lifetime degradation in the sources is related to the gettering efficiency of boron in silicon. This novel simultaneous diffusion, in-situ oxidation, impurity filtering and gettering technique was successfully used to produce 20.3% Fz, and 19.1% Cz solar cells, in one furnace step.

Solar cell efficiencies as high as 18.2% (1 cm2 area) have been achieved using a process sequence which involves impurity gettering on 0.65 Ω-cm multicrystalline silicon (mc-Si) grown by the heat exchanger method (HEM). This is the first time mc-Si device efficiencies have surpassed the 18% mark. Photoconductance decay (PCD) analysis revealed that process induced gettering raised the bulk lifetime (τb) of HEM device material from an as-grown level of 10 μs to 135 μs. Detailed cell analysis shows that for such high τb values, the back surface recombination velocity (Sb) of 10,000 cm/s or higher presents the major efficiency limiting factor for uniform, defect-free devices. It is shown that lowering Sb further can raise the efficiency of similar HEM solar cells above 19.0%. For less efficient devices formed on the same material, the presence of electrically active extended defects are found to be the main cause for the performance degradation. Enhanced gettering or passivation techniques are required to improve these regions of the material

Silicon solar cell efficiencies of 16.9% have been achieved on 0.2 Ω cm float zone silicon, using a simplified cost effective rapid thermal process (RTP). Although the individual processing steps are not fully optimized yet, this represents the highest reported efficiency for solar cells processed with simultaneous front and back diffusion with no conventional high-temperature furnace steps. A diffusion temperature schedule coupled with an added short in situ slow cooling during RTP resulted in greater than 200 μm diffusion length and appropriate diffusion profiles for high efficiency cells. Plasma enhanced chemical vapor deposition (PECVD) of SiN/SiO2 was used for surface passivation and antireflection coating. Conventional cells fabricated by furnace diffusions and oxidations gave an efficiency of 18.8%. Process optimization can further reduce the gap between the conventional and RTP/PECVD cells.

Silicon solar cell efficiencies of 17.1%, 16.4%, 14.8%, and 14.9% have been achieved on FZ, Cz, multicrystalline (mc-Si), and dendritic web (DW) silicon, respectively, using simplified, cost-effective rapid thermal processing (RTP). These represent the highest reported efficiencies for solar cells processed with simultaneous front and back diffusion with no conventional high-temperature furnace steps. Appropriate diffusion temperature coupled with the added in-situ anneal resulted in suitable minority-carrier lifetime and diffusion profiles for high-efficiency cells. The cooling rate associated with the in-situ anneal can improve the lifetime and lower the reverse saturation current density (Jo), however, this effect is material and base resistivity specific. PECVD antireflection (AR) coatings provided low reflectance and efficient front surface and bulk defect passivation. Conventional cells fabricated on FZ silicon by furnace diffusions and oxidations gave an efficiency of 18.8% due to greater short wavelength response and lower Jo

The effectiveness of PECVD passivation of surface and bulk defects in Si, as well as phosphorous diffused emitters, is investigated and quantified with respect to the performance improvement of Si solar cells. Significant hydrogen incorporation coupled with high positive charge density in the PECVD SiN layer is found to play an important role in bulk and surface passivation. It is shown that photo-assisted anneal in a forming gas ambient after PECVD depositions significantly improves the passivation of emitter and bulk defects. PECVD passivation of phosphorous doped emitters and boron doped bare Si surfaces is found to be a strong function of doping concentration. Surface recombination velocity of less than 200 cm/s for 0.2 Ohmcm and less than 1 cm/s for high resistivity substrates (~500 Ohmcm) were achieved. PECVD passivation improved bulk lifetime in the range of 30% to 70% in multicrystalline Si solar cell materials. However, the degree of the passivation was found to be highly material specific. Depending upon the passivation scheme, emitter saturation current density (Joe) can be reduced by a factor of 3 to 9. Finally, the stability of PECVD oxide/nitride passivation under prolonged UV exposure is established