Facile, Multiple Ligands-Assisted Rapid Synthetic Approach Leads to Novel SnO2 QDs

Perovskite solar cell technology has attracted significant global academic and industrial attentions, with the unprecedented efficiency boosting speed. One of the greatest challenges in the perovskite solar cell research is how to reduce the open circuit voltage loss towards S-Q limit, i.e. eliminating the non-radiative recombination loss.

In the paper published in Light Science & Application, a team of scientists, led by Professor Gang Li from Department of Electronic and Information Engineering, Hong Kong Polytechnic University, reported the synthesis of novel electron transport material which significantly suppresses the non-radiative recombination loss. The facile, multiple ligands-assisted, room-temperature rapid synthetic approach leads to novel SnO₂ QDs anchored with multi-functional terminal groups (Figure 1), which function as excellent ETLs to in situ manipulate the interfacial contact in planar perovskite solar cells. Such ligand-tailored SnO₂ QDs exhibited superior properties over the current benchmark materials (e.g., alcohol-based SnO₂ and commercialized colloidal SnO₂).

The ligand-tailored SnO₂ QDs ETLs in planar PSCs show threefold benefits: 1. the ligand-tailored SnO₂ QDs not only passivated perovskite at buried interface with ETL, but also work as seeding-controlling agent to direct the subsequent high-quality perovskite crystallization, resulting in suppressed non-radiative recombination and elongated charge carrier lifetime; 2. the ultrafine SnO₂ QDs act as interfacial "glue" to bridge the perovskite and transparent electrode both chemically and physically (Figure 2), resulting in a favorable electronic and physical interfacial contact; 3. The new SnO₂ QDs ETLs allow the crystallization temperature to be lowered to 100 ℃, providing a new opportunity for flexible substrate manufacturing.

With these improved aspects, the ligand-tailored SnO₂ QDs ETL based devices achieve a high PCE (reverse scan) of 23.02% (certified efficiency 22.51%) in a 1.541 eV bandgap perovskite system. It is noteworthy that a substantially enhanced PCE (V_OC) from 20.4% (1.152 V) to 22.8% (1.242 V, 90 mV higher V_OC, 0.04 cm² device) in the blade-coated 1.613 eV PSCs system, via replacing the widely used benchmark commercial colloidal SnO₂ ETL with the new ligand-tailored SnO₂ QDs. We further investigate the feasibility of the ultrafine SnO₂ QDs ETL in the upscaling of different PSC systems (Eg = 1.541 eV and 1.613 eV respectively) via manufacturing friendly blade coating process. We achieve blade-coated devices with 21.6% (0.98 cm², an impressive V_OC loss of only 0.336 V) in a 1.541 eV and 20.7% PCE (0.8 cm²) in a 1.613 eV perovskite system, representing a record PCE for SnO₂ ETL based upscaling blade-coated PSCs to the best of our knowledge. Moreover, we successfully achieve 30 × 30 mm² mini-modules with 19.5% PCE in 1.541 eV (2 sub-cells) and 18.9% in 1.613 eV (3 sub-cells) perovskite systems.

This in situ solution chemistry engineering of metal oxide synthesis contrives a new direction toward achieving low temperature and high-quality functionalized SnO₂ ETLs, and is compatible with upscaling of large-area high-quality films in perovskite-based photoelectronic devices.