You can freely build on How the First Practical Silicon Solar Cell Works

What this patent covers

This patent describes a device that uses a silicon body to turn sunlight into electrical current to charge a battery. It creates a p-n junction by placing a thin p-type zone, doped with boron, next to an n-type zone. The p-type zone is kept thin—specifically, about the same thickness as the distance electrons can travel before recombining—to ensure electricity is generated efficiently. It also includes a one-way electrical gate, known as a unilaterally-conductive element, to ensure power flows from the solar cell to the battery but prevents the battery from draining back through the cell at night.

What is now free to use

All 1 claims of US 2780765 are in the public domain. Specifically:

• Claim 1: AN ARRANGEMENT FOR UTILIZING SOLAR RADIATION FOR KEEPING CHARGED A STORAGE BATTERY — 1 specific element

The 0 dependent claims add narrowing limitations and are also free.

What is NOT covered

Patent expiry frees this specific invention. Separately-patented improvements made after expiry may still be protected.

• Does not cover solar cells made from materials other than silicon.

• Does not cover solar power systems that lack a battery for energy storage.

• Does not cover the use of non-boron impurities for creating the p-type zone.

• Does not cover solar cells without the specific one-way electrical gate (diode) for preventing battery discharge.

Who is building on this today

Companies like First Solar, SunPower, and JinkoSolar continue to refine the p-n junction physics established here. While the original Bell Labs patent has long expired, the fundamental architecture of the silicon solar cell remains the industry standard.

Products built on expired version of this technology

How to cite this patent in your documentation

Bell Telephone Laboratories Inc. US Patent 2780765. Solar energy converting apparatus. Granted 1957, expired 1974. Now in the public domain.

Note: This is a convenience citation. Consult a patent attorney for formal freedom-to-operate analysis.

PatentBrief is an educational resource and does not provide legal advice. Patent expiration information is derived from USPTO records and may not reflect continuation patents, divisional filings, or separately-patented improvements. For commercial use or production decisions, obtain a formal freedom-to-operate (FTO) opinion from a registered patent attorney.