Holographic nanoscale imaging via femtosecond structured illumination

Introduction

Solution-processed organic and hybrid materials have immense promise for low-cost photovoltaic devices. Their intrinsically heterogeneous morphology directly impacts the photophysical processes that happen over multiple timescales down to femtoseconds and which ultimately define functionality, such as carrier diffusion, charge separation, and recombination.

Current Limitations

Currently, experimental techniques that can simultaneously study the nanoscale morphology and the ultrafast photophysics are limited.

• Ultrafast microscopes are restricted to single point or very small fields of view, lacking the large sample area coverage needed to place observations in their proper statistical context.
• Moreover, they are generally incompatible with super-resolution imaging, preventing the required nanoscale spatial resolution from being achieved.

New Approach

Recently, I introduced a widefield transient holographic microscope using off-axis holography that has shot-noise limited performance and can image large sample areas.

Importantly, this approach is compatible with nonlinear structured illumination, a widefield super-resolution technique based on combining a spatially structured illumination pattern and a nonlinear sample response, with the spatial resolution being only limited by how many nonlinear terms can be acquired.

Project Goals

In HOLOFAST, my team and I will combine the new ultrafast holographic microscope with nonlinear structured illumination to bring unprecedented photophysical knowledge of organic photovoltaic materials, with:

1. Temporal resolution down to 10 femtoseconds
2. Spatial resolution down to 50 nm
3. Simultaneous imaging of ~100 micron areas

This will enable us to finally reveal the heterogeneity of charge separation and extraction processes over large sample areas.

Expected Outcomes

HOLOFAST will create a photophysical and morphological database that will be valuable to understand and solve the problems that currently limit device efficiencies and lifetimes.