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The structures of K or Cs alkaline-treated Cu­(In,Ga)­(S,Se)2 (CIGSSe) solar cells are developed, and their carrier recombination rates are scrutinized. It is determined that short-circuit current density (J SC) is enhanced (decreased optical loss), when ZnS­(O,OH), (Cd,Zn)­S, and Zn0.8Mg0.2O buffers with a large band gap energy (E g) are applied as a replacement of CdS buffer. The J SC is further increased, reducing the optical loss more, when Zn0.9Mg0.1O:B is used as the transparent conductive oxide (TCO) with a larger E g and lower free carrier absorption than those of ZnO:Al. Furthermore, all carrier recombination rates throughout the devices with K or Cs treatment, especially at the buffer/absorber interface and in the quasi neutral region, are reduced, thereby reducing open-circuit voltage deficit (V OC,def), well consistent with the simulated ones. The carrier recombination rate at the buffer/absorber interface is further decreased, when the CdS and (Cd,Zn)S buffers, deposited by chemical bath deposition, are applied, leading to the greater reduction of the V OC,def and the high conversion efficiency (η) of about 21%. Under the trade-off between V OC,def and optical loss, the highest η of 22.6% is attained with the lowest power loss (or the highest V OC × J SC) in the Cs-treated Cd-free CIGSSe solar cell with an optimized structure of glass/Mo/CIGSSe/Zn0.8Mg0.2O/Zn0.9Mg0.1O:B, fabricated by the all-dry process, where the Zn0.8Mg0.2O buffer is prepared by the sputtering method. This occurs because the J SC is the highest attributable to the larger E g of Zn0.8Mg0.2O buffer than those of the CdS and (Cd,Zn)­S.

Cu-deficient layer (CDL) on Cu(In,Ga)Se 2 (CIGS) promotes Cd diffusion from CdS buffer layer and forms a valence band offset (ΔE V ) between CDL and CIGS. We quantitively demonstrate the effects of CDL formation on the performance of CIGS solar cells through experiments and theoretical simulation. To investigate the effects of Cd diffusion and ΔE V by CDL, theoretical analysis was carried out for a CIGS solar cell with a surface layer which simulated the CDL at CdS/CIGS interface. It was revealed that when electron concentration in n-type surface layer is higher than the absolute carrier concentration in CIGS absorber (N D > |N A, CIGS |), open-circuit voltage and fill factor are improved. Additionally, ΔE V ≥ 0.15 eV leads to the highest open-circuit voltage by suppression of interfacial recombination. Transmission electron microscope energy dispersive X-ray spectrometry and scanning spreading resistance microscopy were employed for the same cross section of a CIGS solar cell fabricated by three-stage process. Despite CDL with Cu/(Ga + In) of 0.31 formed on the surface had high Cd contents of 3.4 at%, its carrier concentration of 4.8 × 10 10 cm −3 was lower than that of 10 14 -10 16 cm −3 in grain interior owing to insufficient activation of Cd atoms. These results indicate the effectiveness of ΔE V formation by introducing CDL with low Cu/(Ga + In) of 0.31 to boost CIGS solar cell performance and difficulty in realizing N D > |N A, CIGS | by surface Cd doping.

Cd‐free Cu(In,Ga)(S,Se)2 (CIGSSe) solar cells are fabricated by an all‐dry process (a Cd‐free and all‐dry process CIGSSe solar cell) with aged CIGSSe thin film absorbers. The aged CIGSSe thin films are kept in a desiccator cabinet under partial pressure of oxygen of ≈200 Pa for aging time up to 10 months. It is reported for the first time that aged CIGSSe thin film with increased aging time results in significant enhancement of photovoltaic performance of Cd‐free and all‐dry process CIGSSe solar cells, regardless of the alkali treatment. Based on carrier recombination analysis, carrier recombination rates at the interface and in the depletion region of the Cd‐free and all‐dry process CIGSSe solar cells are reduced owing to avoidance of sputtering damage on CIGSSe absorber surface, which is consistent with the strong electron beam‐induced current signal near CIGSSe surface after the increased aging time. It is implied that the interface and near‐surface qualities are clearly improved through the increased aging time, which is attributable to the self‐forming of Inx(O,S)y near CIGSSe surface, which acts as a buffer layer. Ultimately, the 22.0%‐efficient Cd‐free CIGSSe solar cell fabricated by all‐dry process is achieved with the aged Cs‐treated CIGSSe absorber with the aging time of 10 months.

This paper reports the formation and properties of covalently strapped double helices of bidipyrrin-Zn II complexes, where four dipyrrin chromophores interact with one another by strong exciton coupling.Thorough experimental examination, UV/vis, CD and 1 H NMR spectra, and theoretical studies suggest the existence of two modes of the double helix depending on the dihedral angles between two of the dipyrrin units at the pyrrole a-a bond. In fact, the changes of the modes were observed according to the lengths of straps as well as the temperatures.

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Bidipyrrin-bridged macrocycles, prepared from Ni(II)-bridged dipyrrin-based nanorings by intramolecular oxidative biaryl coupling reactions, yielded [2+4]-type Zn(II)-assisted stable twisted-ring dimers comprising two double helices. These [2+4]-type metal complexes can be optically resolved by chiral HPLC and exhibit tunable electronic and optical properties as a result of spring-like motions. The double helices behave as glue to connect two macrocycles and as the screws of hinges to form thermally responsive synchronized spring systems.