For solar cells to be viable (not relying on government mandates and subsidies) costs have to come down and efficiency must go up. Buried channel solar cells (BCSC) are one possible group of high efficiency devices.
Characteristic for buried channel solar cells are that the front contacts (lighted surface) are placed in deep trenches, formed in silicon crystal. The idea, is to be minimized the width of the contact bars, by the increasing the contact thickness in deep. In this way the formed element has lower shadowing effect and additionally the contact resistance is decreased. The collected efficiency of the created by the light excess carriers is increased too.
Usually p-type Si wafers are used. By diffusion shallow n+ layer is formed on the front surface. By laser or mechanical grooving processes channels are cut. Deep trenches are formed, where the metal contacts have to be placed. The linear velocity of scanning of the places for the contacts bars is slow. After the cut out process the trenches are chemically etched, in order to remove the defects created by the grooving process. The next step is second diffusion for creation of emitter areas. Because of the complicated technological sequence, the production cost of these type elements is higher.
On the basis of patent was experimented new technology for realization of buried contact solar cells. Selectively formed thick porous silicon layer, created by standard anodization process was used. This layer easily could be removed by chemical etching.
This method has technological advantage compared with the used in the moment techniques – laser or mechanical grooving of the trenches.
In our experiments p-type Si wafers of 4–7 Ω.cm conductivity and 325 μm thickness were used to fabricate n+–p–p+ structure based solar cells. The diameter of the wafer was 50mm because of the size of the used Pt electrodes in the electrochemical tank. Porous silicon is a sponge-like fragile structure created in bulk silicon wherein pores are etched into the substrate by electrochemical etching using dilute hydrofluoric acid (10–20% HF concentration typically at 10–100 mA cm2 current density), which results in small silicon skeleton. Holes in silicon react at the surface with negative fluorine ions and dissolve silicon atoms from the substrate lattice. This property has been exploited to create PS selectively in the desired regions. If a p-silicon substrate has distinct n- and p-type regions that can be made easily by a diffusion process, PS will grow only on the p-regions whereas n-type regions will remain intact .
After the anodization step the porous silicon was removed from the surface of the wafer by the chemical etcher HNO3:H2O:HF, which has very good selectivity between PS and crystalline Si substrate .
Cross-section SEM picture of Si wafer after the anodization process
The technological procedure for formation of buried channels (trenches) is absolutely repeated and technologically cleared. The next phase was connected with the filling of the trenches with (Ag–Al) paste. Different technical methods were tested and it was chosen comparatively simple procedure.
I–V characteristics of two types of solar cells; one BCSC solar cells and the reference solar cells with conventional planner contacts (without buried contact, Al sputtered by photolithography) are shown below.
I–V Characteristics of reference and Buried Contact Solar Cells
As a result, the electrical parameters of BCSC are better compared with reference cell, due to the lower contact and sheet resistance in buried contacts compared with the classical planar metallization.
- PHYSICAL SCIENCES
- EARTH SCIENCES
- LIFE SCIENCES
- SOCIAL SCIENCES
Subscribe to the newsletter
Stay in touch with the scientific world!
Know Science And Want To Write?
- Part I: Bee Deaths Mystery Solved? Neonicotinoids (Neonics) May Actually Help Bee Health
- Part II: Bee Deaths And CCD - Flawed Chensheng Lu Harvard Studies Endanger Bees
- Bitcoin And Anonymity: User's Identity Can Be Revealed Much Easier Than Thought
- Not Neonics: Parasites Are Bad For Honey Bees
- Is The Micropower Revolution Here?
- Violence, Sex And Taboo: The Original Brothers Grimm Fairy Tales Back In Print
- Diversity Fatigue: Why Businesses Struggle To Close The Gender Gap
- " This is the start of an article that just appeared in the news letter Catch the Buzz Over 100..."
- "Dear Anonymous: This article was read by all of the entomologists interviewed, including vanEnglesdorp..."
- "I apologize to you and your peers Matthew. It just seems to me that an organization called the..."
- "It is interesting that the fatigue is found in a study from Australia. Let us compare Aussie..."
- "This reminds me of what I read many years ago in Animals Without Backbones by Ralph Buchsbaum.This..."
- DNA may survive suborbital spaceflight, re-entry
- Post-medieval Polish buried as potential 'vampires' were likely local
- Arctic conditions may become critical for polar bears by end of 21st century
- Blistering skin disease may be treatable with 'therapeutic reprogramming,' researchers say
- Carnegie Mellon researchers identify brain regions that encode words, grammar, story