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?
- The Real Meaning Of The Blue Black White Gold Dress
- Men With Short Index Fingers And Long Ring Fingers Are Nicer To Women
- Statistical Mechanics Reveals The Ideal Hideout During A Zombie Takeover
- What Does Your Gut Microbiome Have To Do With Your Immune System?
- Big Data Tackles How Urban Movement Is Linked To Social Activity
- Cruithne: Earth's Other 'Moon' Could Reveal Mysteries Of The Solar System
- Creepy IBM AI toy coming for Christmas—the Continuum paradox. Eerie IBM video link below.
- "Doug:What do you mean by R in your graphs, and the circle with a radius arrow?If, as in the case..."
- "Of course there's one possible explanation for the lack of warming - one that is so obvious, but..."
- "I guess the reason FC persists is that it works! Under appropriate conditions large numbers of..."
- "The researchers conclude that given past historical patterns of variation in the AMO and PMO, this..."
- "Our 5 minute video entry into the Brain Foundation Neurofilm festival to raise awareness about..."
- Robust scientific evidence that chronic fatigue syndrome is a biological illness
- Life 'not as we know it' possible on Saturn's moon Titan?
- For patients with brain tumors, insurance status linked to differences in patient safety and quality of care
- Anti-stroke drugs, minus the side effects
- Local media coverage positive toward local businesses