Erin Ratcliff1
University of Arizona1
The indoor photovoltaic market continues to grow at the same pace as the sensor market, fueled by the continued emergence of the Internet of Things (IoT). One promising strategy to power the IoT are flexible, printable organic photovoltaics (OPVs), which can efficiently harvest/recycle ambient lighting to power small electronic devices. Additional attributes can include recyclability of devices and substrates, preferential color selection for appearance/aesthetics, and low-cost. For wearables in particular, OPVs offer an order of magnitude (or more) in power-per-weight over conventional PV technologies (CIGS, Si, GaAs, etc).<br/>Towards these applications, OPVs devices have a number of interfaces that synergistically lead to high power conversion efficiencies but can also contribute to degradation. Blends of donor and acceptor materials are responsible for both free carrier generation and charge transport through the photoactive layer but phase segregation with time can lead to decreased photoconductivity and reduced fill factors. Charge transfer reactions with oxygen and water can result in chemical changes to the semiconductors, yielding trap states and/or increased recombination pathways. Charge selective contacts are responsible for selectively harvesting one carrier but for metal oxide-based contacts in particular, unpassivated Lewis acid-base sites can result in mid-gap states that promote surface recombination and decreased open-circuit voltages and fill factors.<br/>This talk will focus on a large characterization tool box that allows for investigations of interconnected properties and functionalities of various interfaces in organic photovoltaics from the atomic-to-molecular-to-nanometer-to-device length scales. Emphasis will be placed on understanding contributions to stability and power conversion efficiency retention, with considerations to aesthetics (necessary for wearables and building integrated PV), bond and redox chemistry, microstructure, and photoconductivity. New approaches to <i>operando </i>degradation (degradation of layers under relevant electric fields and charge fluxes) and subsequent characterization of buried interfaces will be discussed.