• Energy Research

In this study thin films of hydrogenated In2O3 (IOH) were fabricated by physical vapor deposition (PVD) with and without a post-annealing step, and by atomic layer deposition (ALD). The electro-opt ...

Abstract Thermochromic (TC) vanadium dioxide thin films provide means for controlling solar energy throughput and can be used for energy-saving applications such as smart windows. One of the factors limiting the deployment of VO 2 films in TC devices is the growth temperature τ s . At present, temperatures in excess of 450 °C are required, which clearly can be an impediment especially for temperature-sensitive substrates. Here we address the issue of high τ s by synthesizing VO 2 thin films from highly ionized fluxes of depositing species generated in high power impulse magnetron sputtering (HiPIMS) discharges. The use of ions facilitates low-temperature film growth because the energy of the depositing species can be readily manipulated by substrate bias. For comparison, films were also synthesized by pulsed direct current magnetron sputtering. Structural and optical characterization of VO 2 thin films on ITO-coated glass substrates confirms previous results that HiPIMS allows τ s to be reduced from ~500 to ~300 °C. Importantly, we demonstrated that HiPIMS permits the composition and TC response of the films to be tuned by altering the energy of the deposition flux via substrate bias. An optimum ion energy of 100 eV was identified, which points at a potential for further reduction of τ s thereby opening new possibilities for industrially-relevant applications of VO 2 -based TC thin films. Weak TC activity was observed even at τ s ≈200 °C in HiPIMS-produced films.

AbstractThis contribution studies the impact of the KF‐induced Cu(In,Ga)Se2 (CIGSe) absorber modification on the suitability of different transparent conductive oxide (TCO) layers in solar cells. The TCO material was varied between ZnO:Al (AZO), ZnO:B (BZO), and In2O3:H (IOH). It is shown that the thermal stress needed for optimized TCO properties can establish a transport barrier for charge carriers, which results in severe losses in fill factor (FF) for temperatures >150°C. The FF losses are accompanied by a reduction in open circuit voltage (Voc) that might originate from a decreased apparent doping density (Nd,app) after annealing. Thermally activated redistributions of K and Na in the vicinity of the CdS/(Cu,K)‐In‐Se interface are suggested to be the reason for the observed degradation in solar cell performance. The highest efficiency was measured for a solar cell where the absorber surface modification was removed and a BZO TCO layer was deposited at a temperature of 165°C. The presented results highlight the importance of well‐designed TCO and buffer layer processes for CIGSe solar cells when a KF post deposition treatment (KF‐PDT) was applied.