@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 = {

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.

}, 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.} } @article {49077, title = {Scanning tunneling microscopy investigation of synaptic behavior in AgInS2 quantum dots: effect of ion transport in neuromorphic applications}, journal = {ACS Applied Nano Materials }, volume = {7}, year = {2024}, month = {MAR}, pages = {7226-7236}, type = {Article}, abstract = {

Scanning tunneling microscopy (STM) is a powerful technique for investigating the nanoscale properties of functional materials. Additionally, scanning tunneling spectroscopy (STS) facilitates the determination of the local density of states (LDOS) within the material. In this study, we present an exploration of the resistive switching (RS) properties and neuromorphic computing capabilities of individual AgInS2 quantum dots, utilizing STM and STS techniques. By examining the material{\textquoteright}s bandgap and its temperature dependence, we uncover a nonlinear variation below the Debye temperature and a linear trend at higher temperatures. Moreover, STS measurements demonstrate changes in the conducting states induced by localized pulses, further confirming the unique characteristics of the quantum dots. The experimental devices constructed by using these quantum dots effectively replicate the RS properties observed at the nanoscale. To assess the neuromorphic application of the devices, pulse transient measurements simulating the learning and forgetting processes were conducted. The gradual set and reset processes successfully mimic the information retention and erasure capabilities essential for neuromorphic computing. Notably, the resistive switching mechanism in these devices is attributed to localized ionic transport, which highlights the significant involvement of ionic species in the observed RS behavior. The outcomes of this study contribute to the fundamental understanding of RS properties in single AgInS2 quantum dots and offer valuable insights into their potential applications in neuromorphic computing.

}, keywords = {corona poling, Ion transport, neuromorphic computing, quantum dots, resistive switching, Scanning tunneling microscopy, STS}, doi = {10.1021/acsanm.3c06272}, author = {Betal, Atanu and Chetia, Anupam and Bera, Jayanta and Saikia, Dibyajyoti and Sharma, Ashish and Rath, Arup K. and Sahu, Satyajit} } @article {49241, title = {Solution-phase ligand engineering for all-quantum-dot near-infrared light-emitting diodes}, journal = {ACS Applied Nano Materials}, volume = {7}, year = {2024}, month = {APR }, pages = {9126-9135}, type = {Article}, abstract = {

Strong emission over a wide near-infrared (NIR) region makes lead sulfide quantum dots (QDs) a preferred material in building NIR light-emitting diodes (NIR-LEDs) for numerous applications. Narrow-bandgap emitter QDs blended in the matrix of high-band gap QDs offer a simple yet powerful architectural platform for building high-performance NIR-LEDs. So far, the all-QD-based blend architecture has been realized using a poorly controlled solid-state ligand exchange approach. Advanced solution-phase ligand exchange, which offers greater control over surface passivation, is yet to be realized in all-QD LED device construction. We observe that the solution-phase ligand exchange from the optimized lead halide and thiol ligand combination, used in high-performing QD solar cell construction, is inefficient in realizing efficient all-QD LEDs, which could have restricted the adoption of the solution-phase ligand exchange thus far. Here, we introduce an innovative dual-ligand strategy to build all-QD-based NIR-LEDs using an advanced solution-phase ligand exchange approach. Through ligand engineering of matrix QDs, we managed to improve photoluminescence quantum yield (40\%), reduce trap density (10(14) cm(-3)), and prolong carrier lifetime (832 ns). The LED devices benefit from improved electronic properties and balanced carrier injection to yield 6\% EQE and 7.7\% PCE, which are six times higher than those of state-of-the-art ligands.

}, keywords = {electroluminescence, lead sulfide, ligand passivation, light-emitting diodes, near-infrared, quantumdots}, doi = {10.1021/acsanm.4c00634}, author = {Biswas, Arindam and Mitra, Anurag and Sharma, Ashish and Shinde, Dipak Dattatray and Dambhare, V. Neha and Sharma, Anjali and Mahajan, Chandan and Rath, Arup K.} }