Colloidal Solution-Processed CuInSe₂ Solar Cells with Significantly Improved Efficiency up to 9% by Morphological Improvement

Abstract

We demonstrate here that an improvement in the green density leads to a great enhancement in the photovoltaic performance of CuInSe2 (CISe) solar cells fabricated with Cu-In nanoparticle precursor films via colloidal solution deposition. Cold-isostatic pressing (CIP) increases the precursor film density by ca. 20%, which results in an appreciable improvement in the microstructural features of the sintered CISe film in terms of a lower porosity, a more uniform surface morphology, and a thinner MoSe2 layer. The low-band-gap (1.0 eV) CISe solar cells with the CIP-treated films exhibit greatly enhanced open-circuit voltage (V(OC), typically from 0.265 to 0.413 V) and fill factor (FF, typically from 0.34 to 0.55), compared to the control devices. As a consequence, an almost 3-fold increase in the average efficiency, from 3.0 to 8.2% (with the highest value of 9.02%), is realized. Diode analysis reveals that the enhanced V(OC) and FF are essentially attributed to the reduced reverse saturation current density and diode ideality factor. This is associated with suppressed recombination, likely due to the reduction in recombination sites at grain/air surfaces, intergranular interfaces, and defective CISe/CdS junctions. From the temperature dependences of V(OC), it is revealed that CIP-treated devices suffer less from interface recombination.

Solvent-free synthesis of Cu2ZnSnS4 nanocrystals: a facile, green, up-scalable route for low cost photovoltaic cells

“…Further studies are accordingly in progress to enhance the densication of the absorber layer. It should be noted, however, that the present result exceeding 6% efficiency was achieved with no additional treatments of the absorber layer, such as mechanical pressing, 43 intentional Na-incorporation, 12,44 chemical etching with KCN or HCl solutions, 44,45 or annealing in a Sn-containing atmosphere. 46 Fig.…”

“…In particular, the shunt conductance (G sh ¼ 0.87 mS cm À2 ) was almost three times higher than that of the low-bandgap CuInSe 2 device with 8.33% efficiency. 43 It is thus suggested that this high G sh together with the high n resulted in the low FF. The TEM crosssectional image of the as-prepared device (Fig.…”

Wurtzite Cu2GeS3 Nanocrystals: Phase‐ and Shape‐Controlled Colloidal Synthesis

“…However, increasing prices of rare metals, such as indium and gallium, hamper further advancement in the field of CIGS thin‐film solar cells. From this perspective, various copper‐based ternary and quaternary chalcogenide nanocrystals, such as CuInS 2 , CuInSe 2 , CuSbS 2 , Cu 3 BiS 3 , Cu 2 FeSnS 4 , Cu 2 ZnSnS 4 (CZTS), and Cu 2 ZnSnSe 4 (CZTSe), have all emerged as potential alternatives . Recently, it was shown that the band gap of Cu 2 SnS 3 and Cu 2 ZnSn(S x Se 4− x ) (CZTSSe) could be tuned by substituting tin with germanium in the crystal lattice, which resulted in enhanced device performance .…”

High-density Cu–In intermetallic nanocrystal layers: towards high-efficiency printable CuInSe2 solar cells

“…21 Furthermore, by employing a cold-isostatic pressing (CIP) technique, it was demonstrated that the microstructure of CISe lms was strongly affected by the packing density of the precursor layers. 22 However, the CIP method is not readily applicable in large-scale production processes due to the complexity of the process.…”