22.4 Solar Cells
635
Fig. 22.67 Schematic
layer stacking of
multi-junction solar cells
and expected efficiency.
Adapted from [1914]
Third Generation Photovoltaics
‘Third-generation’ photovoltaics attempt to go beyond the 30% limit and comprise of multi-junction
solar cells, concentration of sunlight, use of hot-carrier excess energy as discussed above and possibly
other concepts including photon conversion [1907, 1908], intermediate band absorption [1909–1911],
multi-exciton generation [1912] or the use of quantum dots [1913].
In multi-junction cells the different absorber layers are stacked on the substrate with increasing
band gap and connected via (highly doped) tunneling junctions (Sect. 21.5.9). Under 500-fold AM1.5
illumination a three junction (3J) cell (GaInP/GaInAs/Ge) is expected to exhibit up to 41% efficiency,
for 5J 42% or up to 55% using GaInNAs and with 6J up to 59% [1914, 1915] (Fig. 22.67). For a 3J
cell the record efficienvy is 40.7% (240 suns) using the layer structure as shown in Fig. 22.68 [1899].
Details on modeling of III–V multi-junction solar cells can be found in [1916]. In a monolithic cell
the absorbers must be tuned such that the same current (Kirchhoff’s law) can pass through all layers.
Multi-junction solar cells are heteroepitaxial devices and thus expensive; the use of concentration is
economically mandatory.
A recent novel route is a tandem cell comprising of a bottom silicon cell and a top perovskite
cell. Organo-metal halide peroskites, e.g. of the ammonium trihalogen plumbates type, R-N 3 PbI 3 ,
have exhibited quite high conversion efficiencies [1919, 1920] and can be tuned with regard to their
absorption range.
Another concept targeting increased efficiency ands better use of otherwise wasted photons is the
’intermediate band’ solar cell. Here, levels within the band gap of the host, e.g. created by a high
doping with suitable elements or quantum dot levels, shall help absorb below band gap photons and
pump them into the conduction band of the host. A review on this concept and experimental, results
can be found in [1921].
22.4.7 Economic Issues
The cost
12 of producing photovoltaic (PV) modules, in constant dollars, has fallen from as much as
$50 per peak watt in 1980 to as little as 3$/Wp in 2004. The cost of about 0.2 $/Wp in 2020, a third
of the cost in 2012, is realistic and competitive in many applications (Fig. 22.69). The price of solar
power followed for a while Swanson’s law [1925], i.e. a reduction in price by 22% for a doubling of
12 Some of the following information is based on [1922–1924].
635
Fig. 22.67 Schematic
layer stacking of
multi-junction solar cells
and expected efficiency.
Adapted from [1914]
Third Generation Photovoltaics
‘Third-generation’ photovoltaics attempt to go beyond the 30% limit and comprise of multi-junction
solar cells, concentration of sunlight, use of hot-carrier excess energy as discussed above and possibly
other concepts including photon conversion [1907, 1908], intermediate band absorption [1909–1911],
multi-exciton generation [1912] or the use of quantum dots [1913].
In multi-junction cells the different absorber layers are stacked on the substrate with increasing
band gap and connected via (highly doped) tunneling junctions (Sect. 21.5.9). Under 500-fold AM1.5
illumination a three junction (3J) cell (GaInP/GaInAs/Ge) is expected to exhibit up to 41% efficiency,
for 5J 42% or up to 55% using GaInNAs and with 6J up to 59% [1914, 1915] (Fig. 22.67). For a 3J
cell the record efficienvy is 40.7% (240 suns) using the layer structure as shown in Fig. 22.68 [1899].
Details on modeling of III–V multi-junction solar cells can be found in [1916]. In a monolithic cell
the absorbers must be tuned such that the same current (Kirchhoff’s law) can pass through all layers.
Multi-junction solar cells are heteroepitaxial devices and thus expensive; the use of concentration is
economically mandatory.
A recent novel route is a tandem cell comprising of a bottom silicon cell and a top perovskite
cell. Organo-metal halide peroskites, e.g. of the ammonium trihalogen plumbates type, R-N 3 PbI 3 ,
have exhibited quite high conversion efficiencies [1919, 1920] and can be tuned with regard to their
absorption range.
Another concept targeting increased efficiency ands better use of otherwise wasted photons is the
’intermediate band’ solar cell. Here, levels within the band gap of the host, e.g. created by a high
doping with suitable elements or quantum dot levels, shall help absorb below band gap photons and
pump them into the conduction band of the host. A review on this concept and experimental, results
can be found in [1921].
22.4.7 Economic Issues
The cost
12 of producing photovoltaic (PV) modules, in constant dollars, has fallen from as much as
$50 per peak watt in 1980 to as little as 3$/Wp in 2004. The cost of about 0.2 $/Wp in 2020, a third
of the cost in 2012, is realistic and competitive in many applications (Fig. 22.69). The price of solar
power followed for a while Swanson’s law [1925], i.e. a reduction in price by 22% for a doubling of
12 Some of the following information is based on [1922–1924].