Universidad Politécnica de Madrid

Instituto de energía solar

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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