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Effect of Crystal Orientation and Conduction Band Grading of Absorber on Efficiency of Cu(In,Ga)Se 2 Solar Cells Grown on Flexible Polyimide Foil at Low Temperature
Author(s) -
Kim SeongYeon,
Yoo Hyesun,
Rana Tanka Raj,
Enkhbat Temujin,
Han Gyuho,
Kim JunHo,
Song Soomin,
Kim Kihwan,
Gwak Jihye,
Eo YoungJu,
Yun Jae Ho
Publication year - 2018
Publication title -
advanced energy materials
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 10.08
H-Index - 220
eISSN - 1614-6840
pISSN - 1614-6832
DOI - 10.1002/aenm.201801501
Subject(s) - materials science , copper indium gallium selenide solar cells , energy conversion efficiency , polyimide , foil method , solar cell , optoelectronics , substrate (aquarium) , layer (electronics) , analytical chemistry (journal) , composite material , oceanography , chemistry , chromatography , geology
Flexible Cu(In,Ga)Se 2 (CIGS) solar cells are developed on polyimide (PI) foil by using a three‐stage co‐evaporation method. To deposit CIGS on a PI substrate, low temperature deposition process (below 440 °C) is investigated. By optimizing the three‐stage process, power conversion efficiency (PCE) values of 12.1% and 13.6% are obtained at maximum process temperatures of 400 °C and 440 °C, respectively (without anti‐reflection coating). The CIGS absorber deposited at 400 °C is grown with (220)/(204) rather than (112) as its dominant growth orientation, accompanied by highly homogeneous crystal structure and phases. Admittance spectroscopy reveals that the defect levels were lower in the CIGS absorber with (220)/(204) dominant growth orientation, which could have contributed to the PCE of 12.1%. The CIGS solar cell deposited at a temperature of 440 °C exhibits worse defect characteristics compared to that fabricated at 400 °C. However, the CIGS solar cell fabricated below 440 °C exhibited marginal double‐grading of Ga/(Ga + In) in the absorber layer, which resulted in an improved PCE of 13.6%. This result implies that at a temperature below 440 °C, the double‐grading of Ga/(Ga + In) is the more dominant factor causing the PCE improvement above 13%.