Enhancing Hole Transport by Buried Interface Engineering for Scaling-up Perovskite/Silicon Tandem Solar Cells

Abstract

Organic-inorganic metal halide perovskite solar cells (PSCs) have received significant attention over the past decade. In just a few years, the power conversion efficiency of the perovskite solar cells increased from 3.8% to over 26%. They have shown various advantages, including high efficiency, low production costs, and wide applicability. Silicon/perovskite tandem solar cells can achieve excellent power conversion efficiency (PCE) surpassing that of silicon (Si) single cells in the marketplace. Its theoretical limit exceeds 43%, which is much higher than the 33% limit of Si. Si/perovskite tandem solar cell is a stacked structure of perovskite top cell on the Si bottom cell. To make good contact, buried interface engineering of the perovskite top cell is important. The buried interface refers to the layer beneath the perovskite layer but above the transparent electrode. In p-i-n structure, it is a space where hole collection and transport occur. The wettability of perovskite ink and the formation of good hole transport layers (HTLs) can affect the buried interface quality. In this study, RF-sputtered nickel oxide (NiOx) at the buried interface was investigated in Part 1. NiOx improved the wettability of perovskite ink, enhancing hole collection. To apply to commercialization process, RF-sputtering was applied. It can achieve better stability and reproducibility than the solution process. To optimize the sputtered film quality, thickness, oxygen flux, and working pressure were controlled. For high performance, self-assembly monolayer (SAM) was used as HTL. However, SAM tends to aggregate causing micelles in the solution. To prevent this, hydroxyethyl methacrylate (HEMA) as a co-solvent for SAM was introduced in Part 2. HEMA helps maintain non-aggregated SAM and contributes to the formation of a uniform monolayer. In Part 3, scale-up process of bar-coating and vacuum-quenching was studied. Lab-scale solution processes such as spin-coating and anti-solvent are not adoptable at large area fabrication. In scaling up, we faced the morphology and void issues at the buried interface. These issues were enhanced by modifying the perovskite composition and adding an Al2O3 nanoparticle (np) buried interface layer. Triple-halide cation perovskites exhibit an enhanced morphology compared to double halide-cation perovskites. And Al2O3 np improves the wettability of perovskite ink, significantly reducing voids in the buried interface. Finally, we reached a power conversion efficiency of 25.72% of silicon/perovskite tandem device (active area: 1cm2). Moreover, we successfully achieved large-area coating of 7 × 7cm2 using bar- coating and vacuum-quenching processes for wide-bandgap perovskite top cells.