Tandem photovoltaic cells

A system, comprising:

• first and second electrodes;
• first and second photoactive layers between the first and second electrodes, the first photoactive layer comprising a first semiconductor material and the second photoactive layer comprising a second semiconductor material;
• and
• a third layer between the first and second photoactive layers, the third layer comprising a third semiconductor material different from the first or second semiconductor material;
• wherein the system is configured as a photovoltaic system.

A system, comprising:

• first and second electrodes;
• first and second photoactive layers between the first and second electrodes;
• a third layer comprising an n-type semiconductor material, the first photoactive layer being between the first electrode and the third layer and the third layer being between the first and second photoactive layers;
• and
• a fourth layer comprising an p-type semiconductor material, the second photoactive layer being between the second electrode and the fourth layer and the four layer being between the second photoactive layer and the third layer;
• wherein the system is configured as a photovoltaic system.

A system, comprising:

• first and second electrodes, at least one of the first and second electrodes comprising a mesh electrode;
• a recombination layer between the first and second electrodes, the recombination layer comprising a semiconductor material;
• a first photoactive layer between the first electrode and the recombination layer;
• and
• a second photoactive layer between the second electrode and the recombination layer;
• wherein the system is configured as a photovoltaic system.