Alkali-Templated Surface Nanopatterning of Chalcogenide Thin Films: A Novel Approach Toward Solar Cells with Enhanced Efficiency

Abstract

Concepts of localized contacts and junctions through surface passivation layers are already advantageously applied in Si wafer-based photovoltaic technologies. For Cu(In,Ga)Se2 thin film solar cells, such concepts are generally not applied, especially at the heterojunction, because of the lack of a simple method yielding features with the required size and distribution. Here, we show a novel, innovative surface nanopatterning approach to form homogeneously distributed nanostructures (<30 nm) on the faceted, rough surface of polycrystalline chalcogenide thin films. The method, based on selective dissolution of self-assembled and well-defined alkali condensates in water, opens up new research opportunities toward development of thin film solar cells with enhanced efficiency.

Injection Current Barrier Formation for RbF Postdeposition‐Treated Cu(In,Ga)Se2‐Based Solar Cells

“…[25] It was found that similar to a KF PDT, a surface layer forms. [5][6][7][8][9]26,30] Additionally, as presented here for a RbF PDT, with the introduction of a KF PDT, a blocking of the diode current was observed. [15] Recently, Malitckaya et al calculated the bandgap energies of AlkInSe 2 (Alk = Li, Na, K, Rb, Cs) secondary phases, which are expected to segregate on the surface of the CIGS absorber for K, Rb, and Cs.…”

“…Initially, it was found that the KF PDT causes the Cu depletion of the CIGS surface [4] and that a K-In-Se phase forms. [5][6][7][8] Additionally, shown in Figure 1f. A barrier at the front contact is introduced originating from a conduction band offset ΔE C at the iZnO/CdS interface.…”

Point contacts at the copper-indium-gallium-selenide interface—A theoretical outlook

“…Even for an ideal PL, V oc and η don't catch up to the same values. This can be explained by the fact that no perfect passivation of the defects is assumed here, unlike Reinhard et al [10], who modeled the interface between PL and CIGSe without any defects. It is very noteworthy that a significant improvement also occurs for a device having initially a very small interface recombination rate, the efficiency of which should theoretically be limited by recombination in the quasi-neutral region [7,20].…”

“…It can happen due to the diffusion of the atomic elements into the Cu vacancies in the CIGS absorbers, like the Zn diffusion from the ZnS passivation layer [21] or the removal of Cu from the interface and occupation of potassium in the KF treatment [10]. An appropriate etching completely removes the surface oxides before the chemical bath deposition of the buffer layer.…”

“…However, the idea of a point junction was reported by Fu et al by incorporating ZnS nanodots into In 2 S 3 buffer layer, which has been shown to be beneficial for CIGS perfomance [9]. Recently, a novel surface nano patterning technique achieved by self-assembling of alkali condensates make this a method to look for accomplishing PL at CIGS front interface [10].…”