Solar panels capture sunlight and convert it to electricity, using photovoltaic (PV) cells. Each PV cell has several components, including two layers of silicon. One of these layers is injected with phosphorus, which creates an excess of electrons in the layer compared to pure silicon. The other layer is injected with boron, which causes the layer to have fewer electrons than pure silicon. When the two different silicon layers are put together, electrons move from the phosphorus-injected layer to the boron-injected layer. This gives the boron-injected layer a negative charge where the two layers meet, creating an electric field at the junction of the layers.
As sunlight hits a PV cell, electrons in each silicon layer become excited and move around the layer. When any electron reaches the junction between the two layers, the electric field pushes the electron toward metal conductor strips on the outside of the cell, generating electricity.
A diagram of a PV cell being exposed to sunlight is shown below.
GED task: Click on the labels you want to select and drag them into the boxes to show the components of the PV cell.
PV cell — animated overview
Watch electrons get excited by sunlight and pushed by the electric field toward the metal conductor strips
Photovoltaic (PV)
"Photo" = light, "voltaic" = electricity. PV cells convert light energy directly into electrical energy.
Phosphorus layer
Injected with phosphorus → has MORE electrons than pure silicon. This is the TOP layer in the diagram.
Boron layer
Injected with boron → has FEWER electrons than pure silicon. This is the MIDDLE/BOTTOM layer. Gets a negative charge at the junction.
Electric field
Forms at the JUNCTION between the two layers. It pushes excited electrons toward the metal conductor strips — creating electricity.
Step-by-step: sunlight → electricity
1
Two silicon layers are joined The phosphorus layer (more electrons) sits on top of the boron layer (fewer electrons). Electrons naturally flow from phosphorus to boron at the junction, creating a negative charge there and forming an electric field.
2
Sunlight hits the cell Photons (light particles) from the sun strike the silicon layers. The energy from the photons excites electrons — making them "loose" and able to move freely through the layer.
3
Electrons reach the junction As excited electrons move around, some reach the junction between the two layers where the electric field exists.
4
Electric field pushes electrons outward The electric field at the junction pushes these electrons toward the metal conductor strips on the outside edges of the cell. This directed flow of electrons = electric current = electricity!
Key insight: The electric field is the "pump" — it gives electrons a direction to flow. Without it, excited electrons would just move randomly and no useful electricity would be generated. The junction between the two layers is where the magic happens.
Understanding the three components you need to label
🔴 Phosphorus-injected layer
Where: TOP layer of the PV cell Why: Phosphorus adds extra electrons → this layer is "electron-rich" (the "loose" electrons come from here when sunlight hits)
🔵 Boron-injected layer
Where: LOWER/MIDDLE layer Why: Boron removes electrons → this layer has "holes" (fewer electrons). Gets negative charge at junction when electrons flow in from phosphorus layer.
⚡ Electric field
Where: At the JUNCTION between the two layers Why: Formed by the charge difference at the boundary. Pushes excited electrons outward toward the metal conductor strips.
⬛ Metal conductor strips
Where: OUTSIDE edges of the cell Why: These collect the electrons pushed out by the electric field and carry them as usable electrical current.
Label the PV cell diagram
Tap a label from the pool, then tap the correct zone on the diagram. Place all 3 labels correctly!
Labels — tap to select, then tap a zone
Phosphorus-injected layer
Boron-injected layer
Electric field
PV cell diagram — labeled and explained
The fully labeled PV cell showing all four components and how electrons flow
Reading the diagram — what each part shows
Arrows at the top (sunlight): Photons entering the cell from above, exciting electrons in the phosphorus-injected layer
"Loose" electron labels: Show electrons that have become excited and are now free to move through the layer
The wavy junction line: Where the phosphorus and boron layers meet — this is where the electric field exists
Downward arrows at the bottom: Electrons being pushed by the electric field toward the metal conductor strips
Metal conductor strips: On the outer edges — they collect the directed electron flow and output it as electrical current
Correct placement of all three labels
TOP LAYER
Phosphorus-injected layer The top (orange-brown) layer of the cell. Phosphorus adds extra electrons, making this layer electron-rich. When sunlight hits, these are the electrons that become "loose" and excited.
MIDDLE LAYER
Boron-injected layer The middle (blue) layer of the cell. Boron removes electrons, creating "holes." Electrons from the phosphorus layer flow into this layer at the junction, giving it a negative charge and creating the electric field.
JUNCTION
Electric field At the boundary between the two layers. The charge difference at the junction creates this field. It acts as a one-way valve — pushing excited electrons outward toward the metal conductor strips rather than letting them move randomly.
GED strategy — diagram labeling questions
Step 1: Read the passage carefully — the passage always describes what each part does
Step 2: Match each label to a location in the diagram using the passage's clues
Step 3: Look for positional words in the passage ("at the junction," "on the outside," "move from X to Y")
Step 4: Check your labels make logical sense — the electric field must be between the two layers, not outside them
Key clue from the passage: "electrons move from the phosphorus-injected layer to the boron-injected layer" → phosphorus is on TOP (source), boron is BELOW (destination). "creating an electric field at the junction of the layers" → electric field is at the BOUNDARY between them.
