Enhanced Open-Circuit Voltage in Colloidal Quantum Dot Photovoltaics via Reactivity-Controlled Solution-Phase Ligand Exchange

Abstract

The energy disorder that arises from colloidal quantum dot (CQD) polydispersity limits the open-circuit voltage (V_OC ) and efficiency of CQD photovoltaics. This energy broadening is significantly deteriorated today during CQD ligand exchange and film assembly. Here, a new solution-phase ligand exchange that, via judicious incorporation of reactivity-engineered additives, provides improved monodispersity in final CQD films is reported. It has been found that increasing the concentration of the less reactive species prevents CQD fusion and etching. As a result, CQD solar cells with a V_OC of 0.7 V (vs 0.61 V for the control) for CQD films with exciton peak at 1.28 eV and a power conversion efficiency of 10.9% (vs 10.1% for the control) is achieved.

Keywords: colloidal quantum dots; open-circuit voltage; photovoltaics; polydispersity; solution-phase ligand exchange.