@article {46703,
	title = {Reduction of trap and polydispersity in mutually passivated quantum dot solar cells},
	journal = {ACS Applied Energy Materials},
	volume = {3},
	year = {2020},
	month = {SEP},
	pages = {8903-8911},
	type = {Article},
	abstract = {<p>Control over surface passivation is a key to manage the optoelectronic properties in low-dimensional nanomaterials because of their high surface-to-volume ratios. Tunable band gap quantum dots (QDs) are a potential building block for the development of optoelectronic devices like solar cells, photodetectors, and light-emitting diodes. Long and insulating surface ligands of colloidally synthesized QDs are exchanged by short ligands to attain compact arrangement in thin films to facilitate the charge transport process. However, the ligand exchange process often resulted in reduced surface passivation, inhomogeneous QD fusion, and deterioration of energy band gap, which adversely impact their performance in solar cells. Here, we introduce a surface passivation strategy where the QDs are mutually passivated by the organic ligand 3-methyl mercapto propionate and inorganic halometallate ligands to develop a conducting QD ink. The mutually passivated QDs (MPQDs) show significant improvement in optoelectronic properties in maintaining the trap-free energy band gap and size monodispersity. The photovoltaic performance of MPQDs shows a 33\% average increase in power conversion efficiency (PCE) over the conventional halometallate passivation to attain 9.6\% PCE in MPQD solar cells. The improvements in photovoltaic parameters are corroborated by the reduction in density of the intermediate trap states and an increase in depletion width and diffusion length in MPQD-based solar cells.</p>
},
	keywords = {polydispersity, quantum dot, solar cells, surface passivation, trap states},
	issn = {2574-0962},
	doi = {10.1021/acsaem.0c01378},
	author = {Sharma, Ashish and Mahajan, Chandan and Rath, Arup K.}
}
@article {46652,
	title = {Solution-phase hybrid passivation for efficient infrared-band gap quantum dot solar cells},
	journal = {ACS Applied Materials \& Interfaces},
	volume = {12},
	year = {2020},
	month = {NOV },
	pages = {49840-49848},
	type = {Article},
	abstract = {<p>The broad tunability of the energy band gap through size control makes colloidal quantum dots (QDs) promising for the development of photovoltaic devices. Large-size lead sulfide (PbS) QDs, exhibiting a narrow energy band gap, are particularly interesting as they can be used to augment perovskite and c-Si solar cells due to their complementary NIR absorption. However, their complex surface chemistry makes them difficult to process for the development of solar cells. The shape of the QDs transformed from octahedron to cuboctahedron as their size increases, a phenomenon guided by surface energy minimization. As a result, the surface properties change drastically for large-size QDs, which exhibit nonpolar (200) facets and polar (111) facets, as opposed to only (111) facets in small-size QDs. Recent advancements in solution-phase surface passivation strategies, used for the development of high-performance solar cells using the small size and wide band gap QDs, failed to translate a similar enhancement in the case of large-size and narrow band gap QDs. Here, we report a hybrid passivation strategy for large-size and narrow band gap QDs to passivate both (111) and (200) facets, respectively, using inorganic lead triiodide (PbI3-) and organic 3-chloro-1-propanethiol (CPT). By employing charge balance calculation, we identified the desired narrow band gap for QDs to complement the perovskite and c-Si absorption. The distinct choice of the organic ligand CPT enhances the colloidal stability of QDs in the solution phase and improves surface passivation to stop QD fusion in solid films. Photophysical properties show narrower excitonic and emission peaks and a reduction in the Stokes shift. Hybrid passivation leads to a 94\% increase in the power conversion efficiency of solar cells and a 74\% increase in the external quantum efficiency at the excitonic peak.</p>
},
	keywords = {infrared band gap, polydispersity, quantum dot, solar cells, surface passivation, trap states},
	issn = {1944-8244},
	doi = {10.1021/acsami.0c15703},
	author = {Mahajan, Chandan and Sharma, Ashish and Rath, Arup K.}
}
