Unmasking the invisible layers in flexible all-perovskite tandem solar cells

We tend to treat thin films as monolithic slabs. We pour, we spin, we assume uniformity. But at the molecular level, materials have their own agendas. In the pursuit of lightweight power, specifically within the architecture of flexible all-perovskite tandem solar cells, a common conductive polymer has been hiding a secret.

The material in question is PEDOT:PSS. It is the standard hole transport layer for many photovoltaic devices. The assumption? That it forms a consistent, conductive pathway. The reality, observed in this study, is far messier. The researchers uncovered a vertical phase segregation. It seems the PSS component—which is insulating—floats to the surface, leaving the conductive PEDOT trapped at the base. It is a microscopic stratification.

Optimising flexible all-perovskite tandem solar cells

This creates a problem. The PSS-rich surface acts as an insulating cap, inducing interfacial electric dipoles. These dipoles effectively block the extraction of 'holes' (positive charge carriers), capping the device's potential. The physics is clear: if you cannot extract the charge, the cell is inefficient.

The solution proposed is remarkably elegant. The team introduced Triton X-100, a common surfactant often found in laboratories. This additive appears to modulate the polymer interactions. The data measured a distinct disruption of that vertical segregation, resulting in a homogenous film rather than a layered cake. Consequently, the surface dipole formation was suppressed.

The impact on performance is stark. With this modified interface, the researchers achieved a power conversion efficiency of 25.4% for flexible cells. They also constructed a flexible mini-module reaching 19.7%. While current modelling suggests theoretical limits could exceed 24% for modules, this physical proof-of-concept implies that lightweight, bendable solar power for aerospace is moving from theoretical possibility to engineering reality.