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

Abstract

Two strategies for enhancing photovoltaic (PV) performance in chalcopyrite solar cells were investigated: Cu1-xKxIn1-yGaySe2 absorbers with low K content (K/(K+Cu), or x ~ 0.07) distributed throughout the bulk, and CuIn1-yGaySe2 absorbers with KIn1-yGaySe2 grown on their surfaces. For the Ga-free case, increased temperature improved PV performance in the KInSe2 surface absorbers, but not in the bulk x ~ 0.07 absorbers.Growth temperature also increased KInSe2 phase fraction, relative to Cu1-xKxInSe2 alloys-evidence that surface KInSe2 improved performance more than bulk KInSe2.Surface KIn1-yGaySe2 and bulk x ~ 0.07 Cu1-xKxIn1-yGaySe2 films with Ga/(Ga+In), or y of 0.3 and 0.5 also had improved efficiency, open-circuit voltage (VOC), and fill factor (FF), relative to CuIn1-yGaySe2 baselines. On the other hand, y ~ 1 absorbers did not benefit from K introduction. Similar to Cu1-xKxInSe2, the formation of Cu1-xKxGaSe2 alloys was favored at low temperatures and high substrate Na content, relative to the formation of mixed-phase CuGaSe2 + KGaSe2. KIn1-yGaySe2 alloys were grown for the first time, as evidenced by X-ray diffraction and ultraviolet/visible spectroscopy. For all Ga/(Ga+In) compositions, the surface KIn1-yGaySe2 absorbers had superior PV

Revealing the beneficial role of K in grain interiors, grain boundaries, and at the buffer interface for highly efficient CuInSe2 solar cells

“…Overall, the K integration throughout the CKIS absorber and the application of a KIS surface both improve the final CuInSe 2 device. While Ga was excluded from the present study for simplicity, the present growth strategies for K incorporation were confirmed for Ga‐containing alloys up to Ga/(Ga + In) of 0.5 in another study . However, that study and another using RbF PDTs found little or no benefits for CuGaSe 2 …”

“…The diverse absorber/buffer interface effects have impeded consensus regarding the true efficiency enhancing nature of the KF PDT, and a controlled experiment is needed to elucidate these issues. Alternative processing approaches have been used to develop Cu 1‐x K x InSe 2 alloys and Cu 1‐x K x In 1‐y Ga y Se 2 to better understand the KF PDT, particularly the materials chemistry of K in CIGS solar cells.…”

Effects of Copper Substitution by Alkali Metals on the Properties of Chalcopyrites for Tandem Applications: Insights from Theory

“…The resulting observations are coherent with the conclusions from previous sections: the subtsitution of copper with alkali metals widens the band gap of the materials studied. This finding is, in general, in good agreement with the experimental data available (notably for the substitution of Cu by Li and K in CuInS 2 and CuInSe 2 or Rb in CuInSe 2 ) and with other theoretical works: − , the error in the calculated band gap values does not exceed 10%. A recent study accounts for the band gap widening of RbInSe 2 in comparison to CuInSe 2 , according to both experiment and theory.…”

A Comprehensive Perspective on the Fabrication of CuGaSe2/Si Tandem Solar Cells

“…The passivation efforts heal the defects in the absorber bulk and at the absorber/buffer, absorber/back contact interfaces. [ 112–114 ] The defect passivation improves bulk carrier lifetime and diffusion lengths. [ 115 ] Nadenau et al reported the V oc improvements for Na‐containing Ga‐rich CGSe, and Ishizuka et al reported the J sc improvements for PDT‐RbF‐treated CGSe devices.…”