Structural tuning of wide-gap chalcopyrite CuGaSe₂ thin films and highly efficient solar cells: differences from narrow-gap Cu(In,Ga)Se₂

Abstract

Simultaneous realization of high values of open circuit voltage (V oc ), fill factor (FF), and energy conversion efficiency (η) in wide-gap CuGaSe 2 (CGS) solar cells has long been one of the most challenging issues in the realm of chalcopyrite photovoltaics. In this communication, structural tuning of CGS thin films by means of controlling the amount of Se flux used during CGS film growth and improvements in solar cell performance (V oc > 0.9 V, FF > 0.7, and η > 10%) are demonstrated. Systematic variations in CGS film properties with the Se flux and correlation with device properties are shown. The unique CGS thin-film growth kinetics, which are different from narrow-gap Cu(In,Ga)Se 2 , are also presented and discussed. This development of double digit efficiency for CGS solar cells opens a new frontier for the broad application of a new class of chalcopyrite-based devices.

Design of 4-terminal Solar Modules Combining Thin-film Wide-Bandgap Top Cells and c-Si Bottom Cells

“…4(b) and the curve is mathematically fitted with a polynomial function so that the IBC cell efficiency can be expressed by J sc a single variable. Therefore, the efficiency of a hybrid tandem module ( ) with the given IBC bottom cell can be expressed by the equation: [9,10,11]. This offers the possibility to make a hybrid tandem module with an efficiency of over 24%.…”

Revisiting radiative deep-level transitions in CuGaSe2 by photoluminescence

“…5 Due to the highest band gap, the In-free ternary compound is suited for the top cell of a stacked solar cell. But with increasing Ga-content in CIGS, the open circuit voltage loss with respect to the band gap is significantly increased.…”

Optical design of 4-terminal hybrid tandem modules combining thin-film top and c-Si bottom cells

“…5(b), assuming that J sc_sum is equal to 39.8 mA/cm 2 . The shaded area in the figure, in which J sc_t is limited by the band gap of the top-cell absorber material and the product V oc *FF is taken from literature [3,4], indicates the attainable efficiency of the tandem devices with two different top cells. It shows that compared to the single-junction IBC module structure with an efficiency of 19.3%, both a-SiO x :H and CuGaSe 2 top cells can help to increase efficiency in a 4-terminal hybrid tandem device.…”