The power conversion efficiency boost of Cu(In,Ga)Se2 in the past years has been possible due to the incorporation of heavy alkali atoms. Their addition through postdeposition treatments results in an improvement of the open‐circuit voltage, the origin of which has been associated with grain boundaries. Herein, the effect of potassium fluoride postdeposition treatments on the optoelectronic properties of a series of sodium‐free Cu(In,Ga)Se2 single crystals with varying Cu and Ga content is discussed. Results suggest that improvement of the quasi‐Fermi level splitting can be achieved in the absence of grain boundaries, being greater in low‐gallium Cu‐poor absorbers. Secondary ion mass spectrometry reveals the presence of potassium inside the bulk of the films, suggesting that transport of potassium can occur through grain interiors. In addition, a type inversion from n to p in potassium fluoride‐treated low‐gallium Cu(In,Ga)Se2 is observed, which along with study of the carrier lifetime demonstrates that potassium can act as a dopant. The fact that potassium on its own can alter the optoelectronic properties of Cu(In,Ga)Se2 single crystals demonstrates that the effect of postdeposition treatments goes beyond grain boundary passivation.

ZnO nanorod arrays have been grown by potentiostatic pulse electrodeposition between a reduction potential and a "rest" potential. The effect of the duty cycle and pulse frequency as well as the heat-treatment in air on the properties of the electrodeposits has been studied. Surface morphology, structural, optical and electrical properties were evaluated. Absorption spectra reveal a high energy bandgap Burstein-Moss shift for the as-grown nanorods, in line with the donor density (1.1 × 10 19 and 9.5 × 10 19 cm −3 ) determined from electrochemical impedance spectroscopy. After annealing, the carrier concentration decreases to 10 17 -10 18 cm −3 , which is accompanied by an increase of the optical quality of the samples, assessed by the narrowing of the full width at half maximum of the near band edge recombination and steeper absorption at ∼3.3 eV. The donor density and the flatband potential are dependent of the applied duty cycle and pulse frequency. All the analyzed samples evidence deep broad emission bands in the visible region, whose intensity is enhanced after annealing. The defect luminescence is due to an overlap of emitting centers in the red, yellow and green spectral regions, as evidenced and discussed by comparing the steady-state and transient spectroscopies.

Thin film semiconductors grown using chemical bath methods produce large amounts of waste solvent and chemicals that then require costly waste processing. We replace the toxic chemical bath deposited CdS buffer layer from our Cu­(In,Ga)­(S,Se)2 (CIGS)-based solar cells with a benign inkjet-printed and annealed Zn­(O,S) layer using 230 000 times less solvent and 64 000 times less chemicals. The wetting and final thickness of the Zn­(O,S) layer on the CIGS is controlled by a UV ozone treatment and the drop spacing, whereas the annealing temperature and atmosphere determine the final chemical composition and band gap. The best solar cell using a Zn­(O,S) air-annealed layer had an efficiency of 11%, which is similar to the best conventional CdS buffer layer device fabricated in the same batch. Improving the Zn­(O,S) wetting and annealing conditions resulted in the best device efficiency of 13.5%, showing the potential of this method.

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