Self assembled monolayer boosts performance of lead free tin perovskite solar cells

Self assembled monolayer boosts performance of lead free tin perovskite solar cells
by Robert Schreiber
Berlin, Germany (SPX) Aug 06, 2025

Perovskite semiconductors offer promising potential for solar energy due to their thin, flexible structure, high efficiency, and low production costs. However, widespread commercialization remains limited by two critical factors: long-term stability and the presence of toxic lead in high-performing variants.

Researchers at Helmholtz-Zentrum Berlin (HZB) are investigating tin-based perovskite solar cells as a safer, more stable alternative. These lead-free cells exhibit unique electro-optical traits ideal for tandem and triple-junction solar cells, although their efficiency still lags behind lead-containing counterparts.

A significant bottleneck lies in the charge transport layer. Conventional tin perovskite solar cells rely on PEDOT:PSS for the lowest contact layer, a material that introduces inefficiencies and adds complexity to fabrication. While self-assembled monolayers (SAMs) have set new efficiency records in lead-based perovskites, their application in tin variants has so far underperformed.

Principal investigator Dr. Artem Musiienko and collaborators identified the problem using density functional theory, which showed poor interface alignment between the MeO-2PACz SAM and the tin perovskite lattice. This mismatch led to significant recombination losses.

To address this, the team explored alternative SAMs and identified phenothiazine-based Th-2EPT, synthesized by researchers at Kaunas University of Technology in Lithuania. This sulfur-functionalized molecule forms tin perovskite films with good crystallinity and a more favorable interface, reducing electronic losses.

Solar cells using Th-2EPT outperformed those using either PEDOT or MeO-2PACz, achieving an efficiency of 8.2%. "We have demonstrated that the performance of tin perovskite photovoltaics can be significantly enhanced through targeted and rational molecular design," said Dr. Musiienko. Co-author Valerio Stacchini added, "We prove that the higher performance stems from the excellent optoelectronic quality of perovskite grown on the novel SAM."

Research Report:Phenothiazine-Based Self-Assembled Monolayer with Thiophene Head Groups Minimizes Buried Interface Losses in Tin Perovskite Solar Cells