Understanding Photovoltaic Properties of PbS Quantum Dot Solids via Solution Contacting

Photovoltaic (PV) devices based on PbS quantum dot (QD) solids demonstrate high photontoelectron conversion yields. However, record power conversion efficiency remain low, in part due to small photovoltages, which in turn are affected by both bulk and interfacial defects. Their relative impacts on limiting the photovoltaic performance of QD solids are not known. Interfacial defects can be formed when contacting a semiconductor and may dominate the semiconductor/metal or metaloxide junction properties. The objective of this study is to explore whether electrochemical contacting using liquid electrolytes provides means of contacting QD solids without introducing interfacial defects. We have initially focused on the relationship between photovoltages of QD solids and energetics of the contacting electrolytes. We have investigated electrochemical contacting of PbS QD solids using anhydrous liquid electrolytes containing fast, outersphere redox couples. Depending on the energetics of a redox couple, rectifying or nonrectifying PbS QD solid/electrolyte junctions were formed. Results were consistent with electrochemical contacting being a “soft” contacting method that did not introduce interfacial defects as the opencircuit voltage (Voc) varied ideally with solution potential (E), ΔVoc/ΔE = 1.08 ± 0.04. Using this method, we are currently investigating how ligand chemistry of QD solids affects their photovoltages