Researchers from Nanyang Technological University (NTU) have demonstrated fully vacuum‑processed ultrathin perovskite solar cells with MAPbI3 absorber layers down to around 10 nm, achieving multi‑percent efficiency together with high transparency for building‑integrated use.
The team thermally evaporated MAPbI3 in a planar p–i–n architecture and varied the absorber thickness from about 10 nm to several hundred nanometers. Devices with 10 nm, 30 nm, and 60 nm layers reached power conversion efficiencies of roughly 7%, 11%, and 12%, respectively, with open‑circuit voltage and fill factor remaining comparable to conventional 300–900 nm “bulk” devices, indicating low trap density and good optoelectronic quality.
The stack comprises glass/ITO, a Spiro‑TTB hole transport layer with a self‑assembled monolayer, the MAPbI3 absorber, followed by C60 as the electron transport layer, a BCP buffer, and a silver back contact, all realized via vacuum processing. Structural and morphological analysis shows that crystallographic orientation evolves with thickness in a way that supports charge transport, while FESEM and AFM confirm that even 10 nm films are continuous, smooth, and uniform.
Optical studies reveal a thickness‑dependent bandgap widening at ultrathin scales due to quantum confinement, which reduces visible absorption and enhances transparency, particularly in the 30–60 nm regime. As a result, semitransparent devices reach average visible transparency (AVT) values up to about 65%. A 60 nm cell delivers around 41% AVT with approximately 7.6% efficiency, corresponding to a light‑utilization efficiency (LUE) of 3.13, while 30 nm absorbers offer a maximum LUE potential of about 5.15.
The ultrathin cells also perform well under low‑illumination conditions and exhibit near color‑neutral transmission with a color rendering index of about 79.7, making them suitable for window and façade applications. Overall, the 30 nm and 60 nm devices set benchmark LUE figures for ultrathin perovskite solar cells, pointing to a viable path toward scalable, design‑flexible, semitransparent photovoltaics for the built environment.
