The current state of the art in internal additive materials and quantum dots for improving efficiency and stability against humidity in perovskite solar cells

Abstract

The remarkable optoelectronic capabilities of perovskite structures enable the achievement of astonishingly high-power conversion efficiencies on the laboratory scale. However, a critical bottleneck of perovskite solar cells is their sensitivity to the surrounding humid environment affecting drastically their long-term stability. Internal additive materials together with surface passivation, polymer-mixed perovskite, and quantum dots, have been investigated as possible strategies to enhance device stability even in unfavorable conditions. Quantum dots (QDs) in perovskite solar cells enable power conversion efficiencies to approach 20%, making such solar cells competitive to silicon-based ones. This mini-review summarized the role of such QDs in the perovskite layer, hole-transporting layer (HTL), and electron-transporting layer (ETL), demonstrating the continuous improvement of device efficiencies.

Keywords: Electron transporting layer; Hole transporting layer; Passivation; Perovskite solar cells; Quantum dots; Stability.

Graphical abstract

Figure 1

a) The energy diagram illustrates the principle of suppressing surface charge recombination by the insulating layer strategy. The insulating layer of choice suppresses charge recombination by separating the excess electrons and holes in the electron transport layer and perovskite layer, respectively (reproduced with permission [34], copyright 2016, Wiley Online Library); b) The formation process of the mesoporous perovskite device with C₁₂-silane modification (reproduced with permission [37], copyright 2015, The Royal Society of Chemistry); c) The contact angle of unmodified and modified perovskite film of C₁₃–FAS (reproduced with permission [38], copyright 2016, The Royal Society of Chemistry); and d) Schematic diagram showing the interaction mode of 4-DMABA molecules with MAPbI₃ (reproduced with permission [39], copyright 2018, The Royal Society of Chemistry).

Figure 2

Chemical structures of large and small molecules additive materials for increasing the stability of perovskite.

Figure 3

a) Schematic and SEM Image of perovskite surface without and with PEG via spin coating method (reproduced with permission [53], copyright 2016, Nature Communication); b) Chemical formation mechanism of PVP-induced cubic phase CsPbI₃ (reproduced with permission [55], copyright 2018, Nature Communication); and c) Stability of perovskite solar cell without and with PAA under 43% relative humidity in the air with illumination (reproduced with permission [49], copyright 2019, The Royal Society of Chemistry).

Figure 4

Improvement of QDs based perovskite solar cells as a function of the percentage power conversion efficiency (PCE%). Evaluated international journal articles that were published by The Royal Society of Chemistry, American Chemical Society, Nature Publishing Group, The Wiley Online Library, and Elsevier, etc., were searched by using the phrase “Quantum Dots for Perovskite Photovoltaic Devices”.

Figure 5

Possible designs (left) of QD one-pot hydrothermal synthesis of chalcogenic CdTe, CdSe, or CdS with short-chain linker molecules (e.g., N-acetyl-L-cysteine, NAC), which can be exchanged for other linker molecules of interest using thiol chemistry (SH bonding with the QDs of e.g. trioctylphosphine oxide, TOPO), and schematic design of QD-deposited on substrates (right).

Figure 6

Comparison of different power conversion efficiencies with each of QDs for the active layer, HTL, and ETL.