Development of high efficiency wafer bonded 4-junction solar cells for concentrator photovoltaic applications

Abstract

The next generation of multi-junction concentrator solar cells will have to reach higher efficiencies than today's devices. At the same time these solar cells must be reliable in the field, be manufacturable with good yield and at sufficiently low cost. Inevitably the request of higher efficiency requires four or even more junction devices. A four-junction solar cell combination of GaInP/GaAs//GaInAsP/GaInAs with bandgap energies of 1.9, 1.4, 1.1, 0.7 eV is developed in a close collaboration between the Fraunhofer ISE, Soitec, CEA-LETI and HZB. This 4-junction cell hits close to the optimum of theoretical efficiency contour plots and has the potential to reach efficiencies up to 50 % under concentration. Challenges are associated with lattice-mismatch between GaAs and InP which is overcome by direct wafer-bonding. The high cost of the InP is addressed by the use of engineered substrates which only require a 500 nm thin mono-crystalline InP layer instead of several hundr ed m. Excellent solar cell results up to 44.7 % efficiency have been obtained under concentration for devices manufactured on InP bulk substrates. The high cell efficiency is also supported by out-door characterization of one cell below a Fresnel lens with 16 cm2 aperture area. 38.5 % conversion efficiency has been measured for this mono-module in Freiburg under real operating conditions without any corrections

Size-Tuning of WSe2 Flakes for High Efficiency Inverted Organic Solar Cells

“…g ., S, Se, or Te), are studied for a number of applications, ranging from electronics ,, and optoelectronics ,− to spintronics. , In the context of photovoltaics, one promising application for TMDs , is in organic solar cells (OSCs) and, more specifically, OSCs based on the bulk heterojunction (BHJ) concept. , The BHJ structure, which exploits a p-type polymer donor and n-type fullerene acceptor materials (mainly composed by a polymer–fullerene matrix), maximizes the donor/acceptor interfacial area, providing exciton dissociation and charge transfer through the formation of a bicontinuous interpenetrated charge transport network in the active layer. , The introduction of electron and hole blocking (or transport) layers between the polymer donors and acceptors active layer and the anode and cathode, respectively, enables the extraction of photogenerated carriers to the respective electrodes . Bulk heterojunction OSCs are gaining increasing attention due to their low cost, lightweight, and versatility for large-scale fabrication on flexible substrates. , However, until now, the typical performance of OSCs, which is around 10%, does not match that of silicon (power conversion efficiency, PCE, ∼ 25.6%) and other inorganic materials, such as four junction GaInP/GaAs/GaInAsP/GaInAs (PCE ∼ 46%) . The low PCE of OSCs is mainly due to the limited absorption width (approximately 100 nm), the low charge carrier mobility (10 –3 to 10 –5 cm 2 V –1 s –1 for both electron and holes), and the low exciton diffusion length (∼10 nm) of the currently used polymer donors and acceptors active layer. − An option to tackle the limitations of binary BHJ OSCs, and thus significantly improve their PCE, is the addition of a third component material into the active layer, thus forming a ternary BHJ OSC structure .…”

“…26,27 However, until now, the typical performance of OSCs, which is around 10%, 28 does not match that of silicon (power conversion efficiency, PCE, ∼ 25.6%) 29 and other inorganic materials, such as four junction GaInP/GaAs/GaInAsP/GaInAs (PCE ∼ 46%). 30 The low PCE of OSCs is mainly due to the limited absorption width (approximately 100 nm), 31 the low charge carrier mobility (10 −3 to 10 −5 cm 2 V −1 s −1 for both electron and holes), 32 and the low exciton diffusion length (∼10 nm) 33 of the currently used polymer donors and acceptors active layer. 34−36 An option to tackle the limitations of binary BHJ OSCs, and thus significantly improve their PCE, is the addition of a third component material into the active layer, thus forming a ternary BHJ OSC structure.…”

Status of Four-Junction Cell Development at Fraunhofer ISE

“…Another possibility to realise four-junction solar cells is using the direct semiconductor bonding technology. Here a set of sub-cells has been grown on different substrates and thus on different lattice constants and are bonded afterwards [2,14]. Both approaches, the metamorphic growth concept and the wafer bonding technology can also be combined.…”

GaInP/AlGaAs metal‐wrap‐through tandem concentrator solar cells

“…For this reason, they are the candidate of choice for many high‐performance applications such as satellite power generation, high‐concentration photovoltaics (PV) and optical power transmission . Four‐junction solar cells with a record efficiency of 46.1% (at 312xAM1.5d) have been demonstrated by using wafer bonding, and several other device architectures have also been suggested , including inverted four‐junction solar cells which have reached efficiencies up to 45.6% (at 690xAM1.5d) . Typical concentrator solar cell devices in high‐concentration PV modules have dimensions of 1 mm 2 up to 1 cm 2 and operate at concentration levels between 200 and 1500 suns.…”