Butylamine‐Catalyzed Synthesis of Nanocrystal Inks Enables Efficient Infrared CQD Solar Cells

Abstract

The best‐performing colloidal‐quantum‐dot (CQD) photovoltaic devices suffer from charge recombination within the quasi‐neutral region near the back hole‐extracting junction. Graded architectures, which provide a widened depletion region at the back junction of device, could overcome this challenge. However, since today's best materials are processed using solvents that lack orthogonality, these architectures have not yet been implemented using the best‐performing CQD solids. Here, a new CQD ink that is stable in nonpolar solvents is developed via a neutral donor ligand that functions as a phase‐transfer catalyst. This enables the realization of an efficient graded architecture that, with an engineered band‐alignment at the back junction, improves the built‐in field and charge extraction. As a result, optimized IR CQD solar cells (Eg ≈ 1.3 eV) exhibiting a power conversion efficiency (PCE) of 12.3% are reported. The strategy is applied to small‐bandgap (1 eV) IR CQDs to augment the performance of perovskite and crystalline silicon (cSi) 4‐terminal tandem solar cells. The devices show the highest PCE addition achieved using a solution‐processed active layer: a value of +5% when illuminated through a 1.58 eV bandgap perovskite front filter, providing a pathway to exceed PCEs of 23% in 4T tandem configurations with IR CQD PVs.

PbS Colloidal Quantum Dot Inks for Infrared Solar Cells

“…Since the polar BTA solvent will re-disperse and destroy the underlying CQD solid films, fabricating graded CQDSCs using the LSLX method remains a challenge. Kim et al. (2018a , 2018b) solved this issue by using non-polar CQD inks that the BTA was introduced as a phase transfer catalyst to dissolve CQDs forming CQD-BTA complexes.…”

“… (B) Schematic illustration of device architecture for graded CQDSCs and solvent engineering process of the halide passivated CQDs in nonpolar solvents. Adapted with permission from Kim et al (2018a , 2018b) . Copyright (2018) WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.…”

“…The interlayer structure of MoO x /Au/AZO ( Aqoma et al., 2017a , 2017b ) was demonstrated to have an excellent charge recombination effect, in which the island-shaped Au reduced series resistance and increased shunt resistance ( Kim et al., 2017 ). Furthermore, the sputtered dense AZO could protect the organic front cell from being penetrated by the CQD inks, and the CQDs with a low E g were used for back cell fabrication ( Kim et al., 2018a , 2018b ). Kim et al.…”

Orthogonal colloidal quantum dot inks enable efficient multilayer optoelectronic devices

“…Lead chalcogenide CQDs have the advantage of wide-ranging bandgap tunability across the visible to the infrared (IR) (~0.6 eV), extending the PV and photodetector response beyond the c-Si bandgap ( E g = 1.1 eV). In light of their IR absorption, CQDs are promising materials for use in short-wavelength IR photodetectors 12 and as back cells 13 , 14 in tandems with Si ( E g = 1.1 eV) and perovskites (1.58–1.68 eV).…”

Interface Engineering for Both Cathode and Anode Enables Low‐Cost Highly Efficient Solution‐Processed CdTe Nanocrystal Solar Cells

“…Solution‐processed CdTe nanocrystal (NC) solar cells have attracted much attention in recent years because they can be manufactured via solution processing with the feasibility using low‐cost roll‐to‐roll large‐area printing techniques under ambient fabricating conditions . The performance of CdTe NC solar cells has been improved rapidly for power conversion efficiency (PCE) from ≈3% to 8.54% through optimization of NC sintering and n‐type acceptor as well as device architecture .…”