Effects of Sodium and Potassium on the Photovoltaic Performance of CIGS Solar Cells

Surface and bulk effects of K in Cu1−xKxIn1−yGaySe2 solar cells

“…Cu1-xKxInSe2 alloy formation was previously shown to drive Na diffusion out from the substrate [27,33]. This was also observed for Ga/(Ga+In) of 0.3, 0.5 and 1 in the present study (SIMS in Fig.…”

“…The ~29 phenomena associated with KF PDTs have obscured the underlying beneficial mechanisms, although it has been established that a relatively large amount of K is present at the p-n junction in the most efficient solar cells [1]. That observation motivated the study of K bonds in chalcopyrite-based material: Cu1-xKxInSe2 alloys [49,50], control of K bonds in Cu-K-In-Se material using substrate Na [33] and temperature [51], PV performance effects of K at the surface and bulk in Cu1-xKxInSe2 [52], and PV performance [27] and surface spectroscopy [21] of bulk Cu1-xKxIn1-yGaySe2 absorbers with K/(K+Cu), or x ~ 0.07 and Ga/(Ga+In), or y ~ 0.3. These studies on K bonding in chalcopyrites are presently extended to Ga alloys with y of 0 to 1, and connected with surface and bulk mechanisms for PV performance enhancement in Cu1-xKxIn1-yGaySe2.…”

The effect of Na on Cu-K-In-Se thin film growth

“…Recent reports have detailed power conversion efficiency enhancements when potassium fluoride and selenium have been co-evaporated onto Cu(In,Ga)Se2 (CIGS) absorbers at around 350°C (KF post-deposition treatment (PDT)) [1][2][3][4][5][6][7][8][9][10][11]. Although the mechanism(s) responsible for these efficiency improvements are not clear, the KF PDT has been associated with multiple phenomena: increased hole concentration (e.g., by…”

“…consuming InCu compensating donors to produce KCu neutral defects [12]) [5][6][7][8][11][12][13][14], decreased hole concentration (e.g., by consuming NaCu, which produces InCu compensating donors, and may also lead to an increased Mo/CIGS barrier for current flow [8]) [1,8,10], grain boundary passivation [5,15], general defect passivation [2,3], Cu-depleting chemical reaction(s) resulting in better near-surface inversion [1,8,10,16] or decreased valence band energy [14,17,18], morphology changes resulting in increased CdS nucleation sites [2,10], general changes in CdS growth [16], formation of a passivating K-In-Ga-Se [10,19] or K-In-Se [18] interfacial compound, and modified Cu-Ga-In interdiffusion [6,13]. Additional, as-yet-unsubstantiated hypotheses have also been proposed: K could reduce the surface work function [20], interfacial K-Se compounds could cause beneficial effects [15], and detrimental KInSe2 formation could occur [6].…”

Surface and bulk effects of K in highly efficient Cu1-xKxInSe2 solar cells

“…to commercially-relevant chalcogenized CIGS absorbers, [12] full size (0.75 m 2 ) modules, [13] and Cd-free Zn(O,S) buffers. [2,12,22] Although the mechanisms responsible for these efficiency improvements are not clear, the KF PDT has been associated with multiple phenomena: increased hole concentration (e.g., by consuming InCu compensating donors to produce KCu neutral defects [23] ), [5,7,8,11,14,15,19,[24][25][26][27] decreased hole concentration (by consuming NaCu to produce InCu compensating donors, [1] or by forming (K-K)Cu dumbbell interstitial donors [28] ), [1,8,10,16] Na depletion or formation of soluble Na chemical(s), [1,5,7,8,10,13,14,25,26,29,30] Ga depletion at the surface, [1, 8, 10, 13-15, 29, 31, 32] Cu depletion at the surface [7,13,15,18,20] resulting in better near-surface inversion [1,8,10,16,33] or decreased valence band energy,…”