Reduced screen printed aluminum laydown for low cost silicon solar cells

The majority of PV market is covered by p-type c-Si based solar cells, having metal contacts produced by screen printing. Common screen printable Aluminum pastes, due to their chemical properties are able to form deep and effective Back Surface Filed (BSF), providing also low surface recombination velocity. According to the actual industrial state of the art the wet laydown of screen printable Al paste is in the range of 1.4-1.6g per cell, nearly 6-7 mg per printed cm2. This reflects in a cost per cell of 0.02-0.035€. In the roadmap to reduce the solar cell manufacturing costs, a lower laydown is a goal, which also could reflect in lower cell bowing after firing process. However it is not immediate to obtain the same electric performances reducing the Al available to form the BSF. In this paper we investigate the possibility to produce a lower laydown of Al paste which ensures the same electrical performances of a standard Al paste thickness, through the understanding of BSF formation mechanism and electrical properties of the paste in correlation with its formulation. To optimize the effect of the available metal, we have produced several Al pastes by screening different Al powder granulometry mix and frits to obtain good values of Voc, FF and BSF homogeneity comparable to those produced by standard screen printable Al pastes

A new approach: Low cost masking material and efficient copper metallization for higher efficiency silicon solar cells

A new approach based on the development of a new low-cost masking material and a new technique for performing fast wet processes (i.e. chemical etching and electroplating processes) are presented, back side silver removal is proposed allowing in combination with a multi-bus bar module assembly technique to boost standard silicon solar cells towards higher efficiencies at low cost. The new masking material based on a low-cost wax is able to withstand wet hot chemical treatment up to 100 °C. The developed wax composition that costs 10 times less than photoresist can be taken into consideration as an industrial masking process for solar cell for the front copper metallization process. However, the industrial applicability of the copper plating processes foresees several issues concerning the cell throughput for the plating technique at industrial level, which is directly connected to the plating speed. In this work, it is shown how using the new concept of coalescent dynamic liquid drop/meniscus is possible to plate 35 μm thick copper fingers on wax masked solar cell with a deposition speed as high as 1 μm/s. Combining the proposed technique with the back side selective plating, a silver-free silicon solar cell fabrication process is developed allowing to reach efficiencies higher than 18 % for monocrystalline silicon solar cell. © 2015 IEEE

High uniformity and high speed copper pillar plating technique

In this work we report the application of the selective wet processing technique based on dynamic liquid meniscus for copper pillar bumps (CPB) plating. The industrial plating of copper for CPB process is typically carried out at 2 μm/min. A much higher copper deposition rate is necessary to improve throughput for this process. To achieve higher deposition rates of copper the hydrodynamic issue that is natural for all conventional plating baths processes must be solved. A number of solutions is proposed towards realization of high speed and high throughput CPB plating process. Uniformity of copper pillar over a 6-inches silicon wafer is presented and the morphology and shapes of pillars are investigated by scanning electron microscopy (SEM). Copper pillar height and dimension are investigated within different topology over the wafer showing the robustness of the process for the thickness uniformity. Preliminary investigation of the CPB plating shows the uniformity of better than 2 % within 6” silicon wafer

Porous silicon technology, a breakthrough for silicon photonics: From packaging to monolithic integration

Low cost concept based on the porous silicon technology is shown to be well suitable for integrating monolithically the photonic devices on a standard silicon wafers by using localized SOI structures fabricated by electrochemical anodization of silicon wafers followed by thermal oxidation of porous silicon. The new approach consists in realizing buried localized porous oxidized silicon by exploiting two different routes: n- epi/n+/n- structures on p-type wafers and ionimplantation on standard CMOS/BiCMOS wafers. The peculiarities of the developed approach, including anodization and thermal oxidation regimes to form oxidized porous silicon regions with the required properties are presented. The advantages of the proposed approach in realizing the fiber-to-chip and power-over-fiber coupling are discussed. © 2014 IEEE

EXPERIMENTAL ACTIVITY IN THE ENEA-FRASCATI IRRADIATION FACILITY WITH 3-7 MeV PROTONS

A variable energy (3-7 MeV) and pulsed current (0.1 – 100 µA) proton beam has been made available for different applications (radiobiology experiments, detectors development, material studies) in an irradiation facility at ENEA-Frascati based on the 7 MeV injector of the proton-therapy linac under realization in the framework of the TOP-IMPLART Project. It is a 425 MHz linear accelerator consisting in a 3 MeV RFQ followed by a DTL up to 7 MeV (PL-7 ACCSYSHITACHI model) followed by an horizontal and a vertical beam transport line. The latter one is particularly suitable for radiobiology in vitro studies allowing to irradiate besides cell monolayers also cell growing in suspension culture. The paper describes the facility and the recent results of the experimental activity

Attività sperimentali nell’ambito del Progetto TOP-IMPLART

Presso il C.R. Enea di Frascati, nell’ambito del Progetto TOP-IMPLART, è in fase di realizzazione un acceleratore lineare di protoni per Adroterapia. L’iniettore commerciale impiegato opera a 425 MHz ed è costituito da un RFQ da 3 MeV seguito da un DTL da 7 MeV. La facility è caratterizzata dalla presenza sia di una linea di trasporto verticale sia da una orizzontale. La prima è principalmente dedicata alla sperimentazione radiobiologica, allo sviluppo di detector e allo studio di materiali, mentre la seconda sperimenta, nella sezione a media energia, la prima di quattro cavità acceleranti SCDTL (Side Coupled Drift Tube Linac)