Ionic Accumulation as a Diagnostic Tool in Perovskite Solar Cells: Characterizing Band Alignment with Rapid Voltage Pulses

Despite record-breaking devices, interfaces in perovskite solar cells are still poorly understood, inhibiting further progress. Their mixed ionic-electronic nature results in compositional variations at the interfaces, depending on the history of externally applied biases. This makes it difficult to measure the band energy alignment of charge extraction layers accurately. As a result, the field often resorts to a trial-and-error process to optimize these interfaces. Current approaches are typically carried out in a vacuum and on incomplete cells, hence values may not reflect those found in working devices. To address this, a pulsed measurement technique characterizing the electrostatic potential energy drop across the perovskite layer in a functioning device is developed. This method reconstructs the current-voltage (JV) curve for a range of stabilization biases, holding the ion distribution static during subsequent rapid voltage pulses. Two different regimes are observed: at low biases, the reconstructed JV curve is s-shaped, whereas, at high biases, typical diode-shaped curves are returned. Using drift-diffusion simulations, it is demonstrated that the intersection of the two regimes reflects the band offsets at the interfaces. This approach effectively allows measurements of interfacial energy level alignment in a complete device under illumination and without the need for expensive vacuum equipment.

Automated summary

Despite the advancements in perovskite solar cells, understanding the interfaces in these cells remains limited. The mixed ionic-electronic nature of these cells leads to compositional variations at the interfaces, making it difficult to accurately measure the band energy alignment. To address this, a pulsed measurement technique is developed to characterize the energy drop across the perovskite layer in a functioning device. This approach allows for measurements of interfacial energy level alignment in a complete device without the need for expensive vacuum equipment.