Nanoscale AFM Breakthrough: Advanced Characterization Techniques for Next-Generation Solar Cells

The race toward more efficient, stable, and affordable photovoltaic technology has led researchers to an exciting new frontier: the nanoscale. Today, it's widely recognized that a solar cell's macro-level performance stems from complex interactions at the nanometer scale—from the morphology of active layers to the electronic structure of interfaces and charge transport pathways.

This is especially critical for next-generation photovoltaic technologies. In organic solar cells (OSCs), charge generation efficiency depends heavily on the donor-acceptor bulk heterojunction morphology. For perovskite solar cells (PSCs), performance and stability are intimately linked to grain boundary properties, crystalline domain distribution, and nanoscale defects that can trap charges. Even in established silicon technologies, identifying performance-limiting inhomogeneities requires nanometer-scale precision.

Traditional characterization methods have struggled to meet these demands. Standard Conductive AFM (C-AFM) suffers from measurement artifacts like current saturation and limited dynamic range, while conventional Kelvin Probe Force Microscopy (KFM) often lacks the resolution needed to capture subtle electronic variations in advanced materials.

CSInstruments has developed a comprehensive solution combining three revolutionary technologies: High-Definition Kelvin Force Microscopy (HD-KFM™), ResiScope™, and Soft Intermittent Contact (Soft IC) Mode. Together, these innovations overcome conventional limitations and provide unprecedented insights into photovoltaic materials.

HD-KFM™: High-Definition Surface Potential Mapping

HD-KFM™ represents a fundamental shift from traditional KFM techniques. Conventional KFM operates in double-pass "lift mode," scanning each line twice—once for topography and again at 10-100 nm height to measure electrostatic forces. This large separation limits spatial resolution and signal strength.

HD-KFM™ employs advanced single-pass multifrequency excitation. The system mechanically excites the cantilever's first flexural eigenmode for precise topography while simultaneously exciting the second, higher-frequency eigenmode (350-400 kHz) for surface potential. This provides 20-30 times more detection cycles per pixel, dramatically improving signal-to-noise ratio.

Key advantages: detection at 350-400 kHz versus ~17 kHz, 20-30x more cycles, enhanced sensitivity using eigenmode resonance, significantly improved resolution, tip-sample distance under 1 nm versus 10-100 nm, and one-click auto-tune algorithm.

HD-KFM surface potential map of perovskite film showing grain boundaries

For photovoltaic research, HD-KFM™ enables clear visualization of work function variations between donor and acceptor domains in OSCs—a direct indicator of electronic driving force for charge separation.

ResiScope™: Artifact-Free Conductivity Mapping

ResiScope™ overcomes fundamental C-AFM limitations through revolutionary DSP-controlled hardware architecture. Traditional C-AFM relies on fixed-gain amplifiers users must manually select. If conductivity is too high, signals saturate. If too low, signals disappear into noise.

ResiScope™ uses a fast Digital Signal Processor that continuously monitors current in real-time and automatically selects the optimal internal amplifier within microseconds for each location. This enables an extraordinary 10-decade dynamic range in a single scan: resistance from 10² to 10¹² Ω and current from 50 fA to 1 mA.

Comparison of conventional C-AFM vs ResiScope™

Soft ResiScope™: Non-Destructive Characterization

Soft Intermittent Contact (Soft IC) Mode is CSInstruments' "third mode" of AFM. The AFM tip contacts the surface under precisely controlled constant force for measurements, then fully retracts before moving laterally to the next point.

High-resolution ResiScope™ mapping of silicon solar cell

By combining Soft IC Mode's gentleness with ResiScope™'s electrical characterization, Soft ResiScope™ becomes ideal for delicate organic photovoltaic materials.

Multi-Modal Analysis

The Nano-Observer AFM series allows users to switch between Soft ResiScope™ and HD-KFM™ on the same sample area with a single software click. No need to change tips, disengage, or realign—ensuring perfect registration between datasets.

Soft ResiScope™ analysis of P3HT/PMMA organic solar cell

Application Showcase

In P3HT/PMMA organic blends, Soft ResiScope™ current maps clearly distinguish conductive P3HT polymer domains from insulating PMMA matrix, even when topography appears featureless.

For perovskite solar cells, ResiScope™ provides detailed resistance distribution maps crucial for understanding charge transport efficiency and ion migration.

ResiScope™ resistance map of perovskite solar cell film

Conclusion: Empowering Photovoltaic Innovation

CSInstruments' advanced AFM platform provides comprehensive solutions to pressing nanoscale characterization challenges. HD-KFM™ delivers unmatched resolution for mapping surface potential and work function. ResiScope™ enables artifact-free conductivity measurements across 10-decade dynamic range. Soft ResiScope™ offers revolutionary non-destructive characterization of fragile materials.

By transforming AFM into a powerful diagnostic tool, the Nano-Observer AFM Series provides critical insights needed to solve fundamental photovoltaic challenges, accelerating development of more efficient, stable, and cost-effective solar energy technologies.