Universidad Politécnica de Madrid

Instituto de energía solar

R&D at IES

Three terminal heterojunction bipolar transistor solar cells


This is one of our most recent activities. It focuses on the development of the so-called “three-terminal hetero-junction bipolar transistor solar cell” (3T-HBTSC) a concept proposed by our Group in 2015.

The following highlights describe the structure and operation of this novel solar cell (the role of the n and p layers can be interchanged):

  • In the new 3T-HBTSC structure, the top cell is made of the top np layers and is made of a high bandgap semiconductor.

  • In the 3T-HBTSC the bottom cell is actually a heterojunction solar cell consisting of the p middle and n bottom layers. The n middle layer is made of a high bandgap semiconductor and the n bottom layer is made of a low bandgap semiconductor  

  • The key physical principle behind our approach is how to avoid that the voltage of the bottom cell limits the voltage of the top cell. This allows a tremendous simplification of the solar cell structure since, just by the addition of a single semiconductor layer, without the need of a tunnel junction, the increase in photovoltaic conversion efficiency of a multi-junction approach is obtained.

Contact person: Prof. Antonio Martí


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