The ability to print Group IV semiconductor devices from quantum dot inks opens up a pathway towards lower cost, lower energy, and larger area semiconducting devices that retain the benefits of quantum confinement—potentially leading to a paradigm shift for the semiconductor industry. Achieving this goal in nanoparticles is complicated by the same properties that make Group IV materials so desirable in bulk form, namely the long mean free path, the ability to form stable robust oxides, and control over surface passivation.
In this overview talk, I will discuss the challenges in preparing semiconducting thin films (~100 nm to 1 micron) from printed solutions of colloidal silicon and germanium quantum dots with focus on the role of the surface passivation and the ligand exchange. The electrical, optical and structural properties of the quantum dot thin films will be compared to the colloidal solution properties and bulk system properties. I will describe the properties of the resulting photoconductors and photovoltaic devices prepared using bulk-heterojunction (i.e. TiO2) device structures that retain the properties of the quantum dots, such as high absorption coefficient and band-gap tuning. I conclude by discussing the importance of doping in quantum dot Si and Ge inks in the context of pn junctions and also compare the properties of thin films printed from colloidal-solution versus plasma-fabricated quantum dots.