What is the difference between Conventional PV Solar Cell and Tandem Solar Cells? This article is the first part of a bipartite article where we aim to compare the conventional photovoltaic (PV) cells with the tandem solar cell. This comparison includes assessing construction properties and design as well as efficiencies of these two types of cells.
A conventional PV cell that is made up of silicon has one single active layer to harvest Sun’s power and can utilize only a specific portion of the sunlight spectrum. There is also a limitation to the efficiency of this type of cell. This limitation is known as Shockley Queisser Efficiency Limit or SQ Limit. Theoretically, it is around 33% which is intensely related to the crystalline lattice of silicon.
There are also 2 types of PV cells, known as p- or n-type. The division comes from the choice of elements from the third or fifth group of the periodic table of elements as the dopant (impurity) element in the crystalline lattice of silicon. Use of Boron (3rd), results in a p-type PV cell and the use of Gallium (5th) would end up in the n-type cell.
|Cell Type||Active layer||Efficiency Limitation||Effective Spectrum|
|Conventional PV cell||One layer||⩽30%||Red Spectrum of Sunlight|
|Tandem solar cell||Unlimited||⩽86.8%||All Spectrum of Sunlight|
In contrast to the conventional PV cell, tandem solar cells contain two or even sometimes four active layers. they are referred to as multijunction solar cells. Thanks to a couple of layers to capture sunlight, they can harness a wider spectrum of sunlight compared to PV Cells.
The perovskite – silicon tandem solar cell is one of the typical tandem solar cells, which has only two layers (Figure X). The upper perovskite layer is responsible for generating a photocurrent by harnessing the short-wavelength light while the bottom silicon layer uses long-wavelength light to generate charge carriers.
Recently, scientists at the Helmholtz Zentrum Berlin (HZB) have reached a world efficiency record for a perovskite – silicon tandem solar cell in the lab. They achieved a 29.15% efficiency for a device with 1cm² surface. This is so close to the earlier mentioned SQ limit for the conventional PV cells, but the next target for the HZB group is to reach 35% efficiency for this type of tandem solar cells. Reaching this goal would take the efficiency level limits to a different level. The general several layers of tandem Solar Cells have a theoretical efficiency limit of 86.8%.
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