2‐step process for 5.4% CuGaSe₂ solar cell using fluorine doped tin oxide transparent back contacts

Abstract

As single‐junction solar cells are approaching theoretical limits, multijunction solar cells are becoming increasingly relevant, and low‐cost wider bandgap light harvesters in tandem with silicon are the next frontier in thin film photovoltaic research. Cu‐based chalcogenide compounds have achieved great success as standard absorbers, but performance for bandgaps above 1.5 eV is still lacking. Additionally, the use of transparent back contacts remains challenging for this class of materials. In this work, we report on the fabrication of wide bandgap CuGaSe2 absorbers by a combination of metallic sputtering and reactive thermal annealing grown on transparent fluorine‐doped tin oxide‐coated glass substrate. The annealing temperature is carefully tuned in regard to material and photovoltaic device properties. The introduction of an ultrathin Mo interlayer at the CuGaSe2/back interface favors a higher contact's ohmicity and results in an important improvement of all figures of merit. A record conversion efficiency of 5.4% is obtained, which is the highest value reported for this class of absorber on transparent back contact. Fundamental material characterization of the as‐grown CuGaSe2 films reveals a better homogeneity in Cu distribution throughout the absorber's thickness when using a Mo interlayer, along with an enhanced crystalline quality. The sub‐bandgap transparency of the final device remains perfectible, and improvement pathways are proposed using transfer matrix‐based optical modeling, suggesting to use more specular interfaces to enhance optical transmission.

2D hexagonal CuGaSe2 nanosheets by a microwave assisted synthesis method: photoresponse and optical study for optoelectronic applications

“…This material family is relevant in many fields, including non-linear optical, optoelectronic, and photovoltaic devices. [1][2][3] Accurate knowledge of these materials is crucial for many applications. Despite the considerable research on these materials, this knowledge is still incomplete.…”

Silver Alloying in Highly Efficient CuGaSe2Solar Cells with Different Buffer Layers

“…So far, the highest efficiencies of CuGaSe 2 solar cells on TBCs are much lower, at about 5%. [23][24][25][26] Recently, research on the topic of TBCs has intensified and significant progress was observed, lifting the efficiency (η) of chalcopyrite solar cells with TBCs close to the level of those with standard Mo back contacts. [27][28][29][30][31][32][33] Thus, further improvements may be expected in the near future.…”

“…So far, the highest efficiencies of CuGaSe 2 solar cells on TBCs are much lower, at about 5%. [23][24][25][26] Recently, research on the topic of TBCs has intensified and significant progress was observed, lifting the efficiency (η) of chalcopyrite solar cells with TBCs close to the level of those with standard Mo back contacts. [27][28][29][30][31][32][33] Thus, further improvements may be expected in the near future.The best V OC values for CdS-buffered samples are achieved after a postannealing at 200 °C, reaching 971 mV for a polycrystalline [34] and 946 mV for a single-crystal absorber.…”