Abstract:

Nearly all of the emerging photovoltaic (PV) technologies that have developed over the past two decades have been preceded by time-resolved optical spectroscopic investigations of the photoactive layers that comprise the devices. Transient absorption (TA) spectroscopy has revealed photoinduced electron transfer from the primary light harvesting materials to electron acceptors in systems such as organic photovoltaics; while time-resolved photoluminescence (TRPL) has demonstrated long carrier diffusion lengths in the most efficient class of emerging PVs, the perovskites. Time-resolved spectroscopies have accelerated the search for new material systems to serve as PV active layers, while simultaneously enabling an understanding of the losses within PV devices.

Organic (OSC) and perovskite (PSC) solar cells are two of the emerging PV technologies with the greatest potential, reaching power conversion efficiencies of up to 19% and 26% for single junction devices, respectively. Despite their impressive advances, both technologies suffer from losses in efficiency and stability arising from interfaces between the photoactive layers and charge-selective transport layers (CTLs). Recently, conventional CTLs based on semiconductor thin-films have been replaced with molecularly-thin CTLs (MTLs). These MTLs, being only a single molecule in thickness, are ideal CTLs due to their propensity to bond to transparent electrodes, the lack of dangling bonds at their surfaces, and their charge selectivity. This class of materials includes self-assembled monolayers (SAMs) and two-dimensional (2D) semiconductors.

In this talk, I will describe some of our studies on the photophysical processes that emerge at interfaces between MTLs and organic and perovskite active layers, as revealed through transient spectroscopies. I will discuss our results on charge generation, transfer, and separation that occur when a conjugated organic material, BTP-4F (i.e., “Y6”) is interfaced with a 2D MoS₂ monolayer. I will then discuss our results on disentangling the competing effects of charge transfer and interfacial recombination at perovskite-SAM interfaces. Finally, I will discuss our work on understanding the interface between conjugated polymers and SAMs, and the impact that SAMs have on the optical and morphological properties of the polymer.

Bio:

Christopher Petoukhoff is currently a KGFP fellow in the KAUST Solar Center, within the Ultrafast Dynamics Group. He received his PhD in 2017 from Rutgers University in Materials Science and Engineering under the supervision of Prof. Deirdre O’Carroll. During his PhD, he was awarded with a Corning, Inc. fellowship, an NSF-IGERT traineeship, and an NSF-EAPSI – JSPS Summer fellowship. He transitioned to Okinawa Institute of Science and Technology (OIST) as a postdoc in 2017 to undertake research on ultrafast spectroscopy of solar energy materials. Christopher joined KAUST in 2022 to pursue his research interests in predicting, understanding, and mitigating losses in organic and perovskite solar cells. He combines time-resolved and steady-state optical spectroscopies with optoelectronic simulations and morphological characterization to understand and predict performance and stability losses. He has been working towards mitigating these losses using nanophotonic structures, nanomaterials, and interfacial energy level alignment.