(1) Basic structure of I-V group tandem solar cells
Two-terminal GaInP/GaAs/Ge (2-terminal) triple-junction GaAs solar cell consists of 3 sub-cells, namely GaInP top cell, Ga(In)As middle cell, Ge bottom cell, according to the band gap from large to small constitute. Among them, the GaInP top cell and the GaAs middle cell, the GaAs middle cell and the Ge bottom cell are connected by a tunnel junction, and the electrode and the semiconductor are connected by ohmic contact. Each sub-cell consists of a window layer, an emission region, a base region, and a back field (BSF). The window layer is usually a wide bandgap material, and its function is to passivate the surface state of the emitter and reduce the surface recombination rate. Because surface states are often recombination centers for minority carriers. The emitter region and the base region constitute the P-N junction, which is the core of the solar cell to generate photogenerated carriers. The material of the back electric field layer is also a wide bandgap material, which acts as a potential barrier to prevent the diffusion of photogenerated carriers to the surface, reducing the recombination of the back surface, thereby reducing the dark current.
(2) Equivalent circuit of I-V tandem solar cell
In the energy storage system, it can help to understand the working principle and the working characteristics of solar cells. The equivalent circuit diagram of the solar cell shows the equivalent circuit of a 2-terminal GaInP/GaAs/Ge three-junction solar cell. The solar cell can be regarded as a current source that stably generates photocurrent, and one is connected in parallel with a forward bias voltage. shunt resistor below, and 3 diodes in parallel. ISCl, ISC2, and ISC3 represent the photo-generated currents of the top cell, middle cell, and bottom cell, respectively; each sub-cell is in an electrical series relationship, and the smallest current among the three photo-generated currents will be the output limiting current of the three-junction cell; Rsh1, Rsh2 , Rsh3 and R Rs1, Rs2, Rs3 represent the parallel resistance and series resistance of the top cell, middle cell and bottom cell, respectively; the three diodes are the diffusion-limited current Idiff, the space-charge compound current (Space-charge) Recombination Current) Iree, Tunneling Diffusion Current (Tunneling Diffusion Current) Itun. The sum of Idiff, Iree, and Itun is the reverse saturation current.