Pablo Ferrada

Local Doping Profiles for Height-Selective Emitters Determined by Scanning Spreading Resistance Microscopy (SSRM)

In order to confirm the existence of a height-selective emitter, we compared local doping profiles of such emitters with profiles of a standard homogeneous emitter. The concept of a height-selective emitter is based on the classical selective emitter but in a smaller scale. The pyramid tips are highly doped. The sides and valleys are lowly doped. The comparison of the doping profiles was addressed by using a high-spatial-resolution analysis method: scanning spreading resistance microscopy. The measurement was performed on fully produced cells with a height-selective emitter and a standard homogeneous emitter, both with random pyramid textured surfaces. We prepared samples from these cells and investigated the cross sections. A representative pyramid of each type of emitter was selected. We found that for height-selective emitters the surface concentration can strongly vary depending on the measured position of the selected pyramid. The tip of the pyramid is heavily doped, while the bottom is lowly doped. For standard cells with a homogeneous emitter, the doping profiles do not differ dramatically as for the sample with a height-selective emitter. We calculated the local sheet resistance by using the measured local emitter profiles and a doping-dependent mobility model for phosphorus-doped silicon.

SELECTIVE CHEMICAL ETCHING FOR STUDYING THE FRONT SIDE CONTACT IN THICK FILM SCREEN PRINTED CRYSTALLINE P-TYPE SILICON SOLAR CELLS

Crystalline silicon solar cells are currently the leading technology in the photovoltaic market with no great expectable change in the shares. The scientific community works on the further development and improvements of state-of-the-art as well as new solar cell materials. This paper reports on a chemical methodology for selective etching to study the metallization step in monocrystalline silicon solar cells. The object of study is a complete processed silicon solar cell which was cleaved via laser beam on the back side and broken per hand to obtain stripes of the size 15.6×1 cm2. In the following a sequence of etching chemical solutions to selectively remove the components of the front side silver contact was applied. Scanning electron microscopy was used to investigate contact interface after each etching step. The silver finger, the glass and the silver crystallites grown in silicon could be removed. It came out that the silver crystallites preferably grow at the pyramid tips and edges of the textured wafer. A characterization with Energy Dispersive X-Ray Spectrometry was performed to quantify the components of the silver contact after each chemical etching step. While the weight percentage of silver reduced by more than 90% after an aqua regia treatment, it increased by 13% after hydrofluoric acid. Silver was practically eliminated after a second aqua regia bath. Similarly, the content of glass was also determined. The approach serves for interface investigations in semiconductor technology where screen printing approaches are used for the metallization.

Evaluation of incentive mechanism for distributed generation in Northern Chile

Chile is committed to the development of non-conventional renewable energies, so to create the necessary incentives, several laws has been issued. One of the most recent actions was the Net billing law, which seeks to promote the integration of renewable technologies in the distribution segment. Because Chile has chosen not to use subsidies, only cost-efficient technologies are incorporated in the market. The net billing law has not shown much impact so far, therefore further incentive mechanisms are under discussion. This paper reports on the integration scheme for residential photovoltaic generation within net billing and net metering context. Different options of photovoltaic plants are analyzed: a) self-consumption, b) self-consumption and feeding into the grid, c) self-consumption and storage. Discrimination of the best options has been determined based on the economic benefits of each alternative, which are determined by performing calculation of Net Actual Value (VAN). Growth rates for each of sizing options have been also determined and compared with the price of energy for the residential segment (BT1) in order to find the optimal choice. The results obtained show that for the existing market conditions in Chile and the net billing scheme the size of the photovoltaic plant in northern Chile should be about 1 kW. Furthermore, the option of using storage is not yet economically feasible.