The effect of Zn_1−xSn_xO_y buffer layer thickness in 18.0% efficient Cd‐free Cu(In,Ga)Se₂ solar cells

Abstract

The influence of the thickness of atomic layer deposited Zn 1Àx Sn x O y buffer layers and the presence of an intrinsic ZnO layer on the performance of Cu(In,Ga)Se 2 solar cells are investigated. The amorphous Zn 1Àx Sn x O y layer, with a [Sn]/([Sn] + [Zn]) composition of approximately 0.18, forms a conformal and in-depth uniform layer with an optical band gap of 3.3 eV. The short circuit current for cells with a Zn 1Àx Sn x O y layer are found to be higher than the short circuit current for CdS buffer reference cells and thickness independent. On the contrary, both the open circuit voltage and the fill factor values obtained are lower than the references and are thickness dependent. A high conversion efficiency of 18.0%, which is comparable with CdS references, is attained for a cell with a Zn 1Àx Sn x O y layer thickness of approximately 13 nm and with an i-ZnO layer.

Growth of amorphous Zn–Sn–O thin films by RF sputtering for buffer layers of CuInSe2 and SnS solar cells

“…An amorphous structure has some advantages, such as the lack of a grain boundary, and the effect of the lattice mismatch with the p-type photoabsorber is negligible in amorphous thin films. As a result, the number of interface defect states may be reduced, which may thereby decrease the interface recombination current [17][18][19].…”

“…However, using an amorphous structure results in interesting properties because there is no grain boundary, and the effect of lattice mismatch with the ptype photoabsorber is negligible in amorphous thin films. As a result, the number of interface defect states may be reduced by using α-ZTO grown by atomic layer deposition as a buffer layer, which may thereby decrease the interface recombination current [17][18][19]. We revealed that sputtering damage to the pn-interface of a CIGS solar cell can be …”

The effect of substrate temperature on atomic layer deposited zinc tin oxide

“…An advantage of the ZTO material as a buffer layer is that its band gap and conduction band offset can be tuned by changing the [Sn]/([Zn] + [Sn]) ratio [7,13,15], which possibly enables an improved conduction band alignment to different CIGS surface compositions. Another advantage is that it only takes a ZTO film thickness of about 15 nm to fabricate highly efficient CIGS solar cells [3] with a demonstrated conversion efficiency of up to 18.2% for a 0.5 cm 2 cell [4], which is comparable to CdS buffer layer reference cells.…”

“…Zinc tin oxide, Zn 1 − x Sn x O y (ZTO) is a wide band gap semiconductor material that has a possible new application in photovoltaics, where it is used as a cheap, earth abundant and non-toxic buffer layer alternative for thin film Cu(In,Ga)Se 2 (CIGS) [1][2][3][4], cadmium telluride (CdTe) [5,6], metal-oxide [7] and inverted organic solar cells [8]. One buffer layer deposition technique that has proven suitable for making highly efficient CIGS solar cells is atomic layer deposition (ALD) [9].…”

Comparative study on structural, morphological and optical properties of Zn2SnO4 thin films prepared by r.f. sputtering using Zn and Sn metal targets and ZnO–SnO2 ceramic target

“…This makes ZTO a very interesting material for a wide panel of applications in electronics and optoelectronics, including transparent electrode for solar cells [3][4][5], chemical and gas sensors [2], light emitting diode and lasers [4], transistors [6], etc. Last but not least, ZTO thin film recently deposited by atomic layer deposition [7][8][9][10] and r.f. sputtering [11], successfully replaces cadmium sulphide as buffer layer in the p-n junction in Cu(In,Ga)Se 2 solar devices, due to its high optical transmittance in the visible light region.…”