Colloidal Quantum Dot Photovoltaics Enhanced by Perovskite Shelling

Abstract

Solution-processed quantum dots are a promising material for large-scale, low-cost solar cell applications. New device architectures and improved passivation have been instrumental in increasing the performance of quantum dot photovoltaic devices. Here we report photovoltaic devices based on inks of quantum dot on which we grow thin perovskite shells in solid-state films. Passivation using the perovskite was achieved using a facile solution ligand exchange followed by postannealing. The resulting hybrid nanostructure created a more intrinsic CQD film, which, when incorporated into a photovoltaic device with graded bandstructure, achieved a record solar cell performance for single-step-deposited CQD films, exhibiting an AM1.5 solar power conversion efficiency of 8.95%.

Single-step colloidal quantum dot films for infrared solar harvesting

“…To achieve this, we improved upon an anti-solvent phase-boundary exchange method used for 1.3 eV CQDs. 7,8 In this process, oleic-acid (OA)-capped PbS CQDs (OA-PbS) dispersed in octane are mixed with halide precursors that are dissolved in N,Ndimethylformamide (DMF). Previous work on anti-solvent phase boundary exchanges had used methylammonium iodide 7 and methylammonium lead tri-iodide for the ligandexchange process.…”

“…Previous work on anti-solvent phase boundary exchanges had used methylammonium iodide 7 and methylammonium lead tri-iodide for the ligandexchange process. 8 Here, we use lead iodide (PbI 2 ) that can also act as a ligand, which has recently been shown to increase short-circuit current in a solid-state treatment. 9 Further, the iodide ligands have been demonstrated to be stable under air storage.…”

“…Typically, n-butylamine (BTA) is used as a final solvent for 1.3 eV halide-capped solution-exchanged CQDs. 7,8 We first attempted to form a stable colloid of 1 eV PbI 2 -PbS nanocrystals in BTA. However, we found that a large proportion of the CQDs instantly agglomerated and could not be redispersed in the solvent.…”

Solid‐State Ligand‐Exchange Fabrication of CH3NH3PbI3 Capped PbS Quantum Dot Solar Cells

“…As shown in Figure 3c and Table 1, among the devices with active layer numbers of 3, 5, 7, and 10, respectively, the five‐layer device exhibits an optimum PCE of 4.25% with a J sc of 24.83 mA cm −2 , an open‐circuit voltage ( V oc ) of 0.45 V, and a fill factor (FF) of 38%. Note that this PCE is significantly higher than those reported values of traditional EDT‐capped PbS solar cells (≈3%) 7, 8, 24, 25. It is also notably higher than those of EDT capped PbS/CH 3 NH 3 PbI 3 core/shell QDs sensitized solar cells (3.2%)30 and CH 3 NH 3 PbI 3 /oleic acid capped PbS bilayer heterojunction photovoltaic cells (3.6%),31 respectively.…”

“…Recent studies showed an effective strategy of improving FF and PCE in the PbS CQD solar cells by inserting a thin top layer of PbS−EDT 24. We therefore added two layers of p‐type PbS−EDT CQDs (≈50 nm)24 onto the optimal five layers of n‐type PbS−CH 3 NH 3 PbI 3 CQDs (≈300 nm) in solar cells to create graded band structures.…”