Efficient, Stable Infrared Photovoltaics Based on Solution-Cast Colloidal Quantum Dots

Abstract

Half of the sun's power lies in the infrared. As a result, the optimal bandgaps for solar cells in both the single-junction and even the tandem architectures lie beyond 850 nm. However, progress in low-cost, large-area, physically flexible solar cells has instead been made in organic and polymer materials possessing absorption onsets in the visible. Recent advances have been achieved in solution-cast infrared photovoltaics through the use of colloidal quantum dots. Here we report stable solution-processed photovoltaic devices having 3.6% power conversion efficiency in the infrared. The use of a strongly bound bidentate linker, benzenedithiol, ensures device stability over weeks. The devices reach external quantum efficiencies of 46% in the infrared and 70% across the visible. We investigate in detail the physical mechanisms underlying the operation of this class of device. In contrast with drift-dominated behavior in recent reports of PbS quantum dot photovoltaics, we find that diffusion of electrons and holes over hundreds of nanometers through our PbSe colloidal quantum dot solid is chiefly responsible for the high external quantum efficiencies obtained in this new class of devices.

Schottky Solar Cells Based on Colloidal Nanocrystal Films

“…This simple ITO/NC/metal device features a higher NC loading and fewer heterojunctions than either NCsensitized Gratzel or NC/polymer blend designs, and outperforms existing lead salt NC solar cells. [24][25][26][27][28][29][30][31][32][33][34] Our work demonstrates that large EQEs are obtainable from NC cells without the need for sintering, superlattice order or separate phases for electron and hole transport. An improved understanding of electronic coupling, surface passivation, doping, and junction formation in NC films will lead to much more efficient and stable NC solar cells in the future.…”

Ionic-passivated FeS2 photocapacitors for energy conversion and storage

“…The quantum dot PVs have been realized using a variety of short mono-and bidentate organic ligands. Ethanedithiol (EDT), aromatic thiols, 19 alkylamines, 20 mercaptocarboxylic acids (MPA) 21 and inorganic ligands 14 have all shown promise in achieving effective passivation while reducing interparticle spacing. We have utilized three different ligands to examine their passivation effects on the performance of FeS 2 photocapacitors.…”

Multiple exciton generation in quantum dot-based solar cells

“…These strategies use for such surface passivation either a ligand sphere of organic [55,82,83] and/or inorganic molecules [49,80,84] [82,83,89]. While QDs passivated with dithiol ligands showed high charge-carrier mobilities [90,91] and competitive device performances in solar cells, no evidence for MEG could be found in devices [26,60].…”

“…The second effect of using hydrazine as a ligand is the very short interparticle spacing; this reduces the width of the tunnelling barrier between QDs thereby increasing carrier mobility of the film as a whole. Both effects are particularly beneficial for holes that are produced via MEG as they are commonly located far away from the holeextracting electrode and are thus prone to recombination during charge extraction [79,82,83].…”