Local growth of CuInSe 2 micro solar cells for concentrator application

Abstract

A procedure to fabricate CuInSe2 (CISe) micro-absorbers and solar cells for concentrator applications is presented. The micro-absorbers are developed from indium precursor islands which are deposited on a molybdenum coated glass substrate (back contact), followed by deposition of copper on top and subsequent selenization as well as selective etching of copper selenides. In order to compare the properties of the locally grown absorbers to those of conventional large area CISe films, we systematically examine the compositional and morphological homogeneity of the micro absorbers and carry out photoluminescence measurements. Preliminary devices for micro-concentrator solar cell applications are fabricated by optimizing the copper to indium ratio and the size of the indium precursor islands. The resulting micro solar cells provide a characteristic I-V curve under standard illumination conditions (1 sun).

Thin-film micro-concentrator solar cells

“…Physical vapor deposition techniques (PVD) have also been proven to be compatible with the fabrication of micro absorbers. Heidmann et al were able to grow micrometer-sized indium islands by PVD [46]. A metallic indium precursor was deposited by PVD onto Mo substrates, which were pre-structured by femtosecond laser pulses [47,48].…”

“…A metallic indium precursor was deposited by PVD onto Mo substrates, which were pre-structured by femtosecond laser pulses [47,48]. This site-selective modification of the Mo surface [49] promoted the localized deposition of In and thus created an easily tunable arrangement of nucleation sites [46][47][48], as schematized in figure 6(a). The In islands were subsequently coated by Cu and converted into CISe by a selenization process, after which excess Cu-Se was removed by a KCN etching step.…”

“…The In islands were subsequently coated by Cu and converted into CISe by a selenization process, after which excess Cu-Se was removed by a KCN etching step. To isolate the cells, a resist layer was spin coated, leaving the upper part of the CISe islands uncovered to be coated by the CdS buffer layer and transparent conductive oxide [46]. In a later work, CIGSe and CISe micro absorbers, such as the one shown in the SEM image in figure 6(b), were fabricated by this sequential PVD on laser-patterned Mo substrates, showing efficiencies up to 1.4% [50].…”

“…Subsequently, a standard selenization process in Se ambient, as well as an etching process by KCN to remove unwanted Cu-Se phases were performed. Solar cell devices were completed, as described before [46]. Although this approach has so far resulted in low efficiencies due to very limited J SC values, the photocurrent does increase as expected under concentrated illumination.…”

“…Inset in (c) shows the difference Δ between experimental efficiency and the expected one. Data taken from (α) [36], (β) [28], (γ) [33], (δ) [44], (ε) [40], (η) [26], (θ) [27], (κ) [51], (λ) [57] and (μ) [46].…”