GaNAsSb 1-eV solar cells for use in lattice-matched multi-junction architectures

Abstract

Photovoltaic devices made from a dilute nitride material, GaAsNSb, with band-gap close to 1eV have been developed and characterised. Homojunction devices of n-on-p and p-on-n type as well as an n-on-p GaAs/GaNAsSb heterojunction have been grown by molecular beam epitaxy. Optical and electrical characteristics are reported and a onedimensional drift-diffusion model of internal quantum efficiency is used to estimate minority carrier diffusion lengths. The GaAs/GaNAsSb heterostructure produced AM1.5G short-circuit current of 23.6 mA/cm 2 , open-circuit voltage of 0.44V and fill factor of 67%. The model suggests that this performance is limited by both diffusion length and surface recombination.

Modelling of lattice matched dilute nitride 4-junction concentrator solar cells on Ge substrates

“…The majority carrier mobility has been found to be on the order of 70 cm 2 /V•s for p-type samples with a weak sensitivity to doping density (8 cm 2 /V•s difference between 1•10 17 and 1•10 18 cm -3 doping level) while n-type samples showed a mobility of 266 and 128 cm 2 /V•s for 1•10 17 and 5•10 17 , respectively. By using TRPL, we have determined the surface recombination velocity between GaAs/GaNAsSb to be on the order of 10 3 cm/s and lifetimes within the range of 0.1-0.5 ns for both p-type and n-type samples in agreement with reference [3]. By using the experimental optical constants (n, k) calculated from ellipsometry measurements, the thickness requirement is estimated to be higher than 2 µm in order to ensure a high light collection (>95%) while an absorber of 3 µm would collect about 98% of the incoming light for the ASTM-G1703 direct terrestrial reference spectrum.…”

“…On one hand, to comply with the current-matching criteria, MBE-grown dilute nitrides have shown better photovoltaic properties than their MOVPE counterparts as demonstrated in [1]. However, the quality of the material is very dependent on specific conditions of in-situ and/or ex-situ thermal annealing treatments and their effect on the evolution of nitrogen related defects and background carrier concentration [3,7]. Therefore, the achievement of a high quality material is not straightforward.…”

10 MeV proton irradiation effects on GaInP/GaAs/Ge concentrator solar cells and their component subcells

“…Even though this indirect technique gives excellent results, it does not provide a direct access to the radiation damage in each subcell. Another motivation to increase the number of degradation studies in conventional 3JSCs is that such structure is the baseline of the socalled 4-junction lattice matched multijunction solar cell which inserts a 1eV dilutenitride cell between the GaAs and Ge subcells [13,14].…”

Structures based on GaAs(Sb)(N) semiconductor alloys for high efficiency multi-junction solar cells

“…Indeed, the band structure of GaAs 1-x-y Sb x N y can be modeled by a double BAC (DBAC) model, which is a combination of a CB BAC model for GaAs 1-y N y and a VB BAC model for GaAs 1-x Sb x [68,69]. Moreover, the The GaAs 1-x-y Sb x N y alloy has been recently applied to solar cell technology, both as a thick layer [52,[71][72][73][74][75][76][77][78][79][80][81][82][83][84] and as a capping layer over InAs quantum dots [85,86]. Nevertheless, the obtained solar cell performance is not satisfactory up to now.…”

“…As was discussed in Chapter 2, GaAs 1-x-y Sb x N y is a suitable candidate for its implementation as 1.0-1.15 eV sub-cell in optimum GaAs/Ge-based MJSCs designs. Bulk layers of GaAs 1-x-y Sb x N y material have already been experimentally tested for MJSC applications [52,72,73,77,[79][80][81][82]84]. However, as far as we know, the efficiencies achieved have not approached the predicted values, mainly due to difficulties in achieving high-quality material [92].…”