Carbon Nanotubes - the p-Type Contact of the Future for Perovskite Solar Cells?

Abstract

The enormous strides researchers have made in advancing perovskite based photovoltaics in the past few years are fueling the dream of a rapid entry of this highly promising technology into the global energy market. This seems like serendipitous timing since solar power has gained an enormous momentum over the past decade exceeding all projections. This expansion in solar power is driven by an increasing understanding that climate change requires immediate action, in particular with regards to power generation; and simultaneously, the price for photovoltaic modules has remarkably quickly fallen to make solar power generation competitive vis-à-vis conventional technologies. Compositional tuning of the perovskite absorber has led to immense improvements in stability and efficiency of perovskite solar cells leading to a certified efficiency of 22.7% for a single-junction laboratory device. The successful transition of a photovoltaic technology from the lab into the field requires, however, two additional important parameters aside from efficiency which are essential for real-world deployment: stability and scalability. We propose using single-walled carbon nanotubes (SWCNTs) as p-type layer for perovskite solar cells for future applications. Carbon nanotubes combine several highly attractive characteristics such as chemical inertness and mechanical resilience with intrinsically high charge-carrier mobilities endowing them with a unique potential to be a very stable dopant-free charge-selective contact. Furthermore, the SWCNT deposition techniques for large-scale use, such as spray-coating, are already well-established, opening clear avenues for direct implementation in a real-world industrial setting. In this study, we demonstrate that employing SWCNTs as hole-transporting material can yield steady-state efficiencies of above 20% for alloyed narrow bandgap perovskites, and of over 7% for wide-bandgap perovskites, illustrating the versatility and excellent performance of SWCNTs as charge-selective contact material.