Evaluating different alkylammonium bromide passivation films to stabilize and enhance PV performance of perovskite solar cells

Abstract

• Optimized the carbon chain length for interface passivation film used in perovskite solar cells. • Demonstrated how the perovskite film quality, performance, and stability are affected by smaller and larger carbon chains. • The optimized device power conversion efficiency was improved to 21.4% from 19% in the control device. • Emphasized on necessity to explore passivation films to extract full potential of perovskite solar cells. 2-dimensional (2D) materials are gaining immense popularity as interface passivation films for perovskite solar cells (PSCs). Among several types of interface passivation films used, long carbon chain alkylammonium bromides are the commonly used option due to their availability, cost, and easy deposition method. These 2D films passivate the boundaries of the cells, but a lengthy carbon chain can affect the carrier conduction in the device. Here, we have optimized the carbon chain length in 2D alkylammonium bromide films, giving the best-performing PV devices. All the 2D passivation films improved the open circuit voltages and fill factors of the devices. The champion cell obtained using n-hexylammonium bromide 2D film showed a power conversion efficiency (PCE) of 21.4%, a 12.6% increase from the control device. Moreover, all the passivated devices were considerably more stable in storage and operational conditions. Surface analysis with atomic force microscopy and scanning electron microscopy showed smoother surfaces with larger grains when 2D passivation films were added. In addition, depth profile measurements showed lower ion migration in the passivated films, directly resulting in mitigating hysteresis in the device in the long term. Overall, adding an optimized 2D passivation film can greatly improve PSCs with minimal extra cost and processing time.