Efficient Perovskite Solar Cells Based on CdSe/ZnS Quantum Dots Electron Transporting Layer with Superior UV Stability

Abstract

Organic-inorganic perovskite materials with their outstanding optoelectronic properties have made a revolution in the field of optoelectronic devices. [1][2][3][4][5][6][7][8] Among all thin film photovoltaics (PVs), perovskite solar cells (PSCs) show a fast progress in a short period of time with high efficiency exceeding 25%, due to their great absorption, long diffusion length, high-quality crystals, low cost, and low-temperature processing. [9][10][11][12][13][14] Over the past years, researchers mostly focused on compositional engineering, interface engineering, additive engineering, and surface passivation approaches to boost the device performance as well as stability. [15][16][17][18][19][20][21][22][23][24][25][26] Apart from extensive efforts of researchers in this regard, stability is still the main challenge in this field. [27][28][29][30] In fact, finding new effective transporting layers for the PSCs is a good strategy to address this issue. [31][32][33] Titanium dioxide (TiO 2 ) is one of the most commonly used electron transporting layers (ETLs) in the PSCs. [13,34,35] However, it suffers from hysteresis and stability issues due to having high amount of oxygen vacancies caused by UV light and also weak charge extraction properties. [36] To address this shortening, double-layer ETL and doping strategy have been proposed by many groups, which can improve slightly the efficiency and stability. [37][38][39] Moreover, employment of new organic and inorganic ETLs such as tin oxide (SnO 2 ) with better transporting properties could be another solution for this issue. [40] However, these strategies cannot protect the PSCs from the UV illumination. Applying downshifting materials on the PSCs is an effective way for this purpose. [41,42] In this study, we propose CdSe/ZnS QDs as a new ETL in the planar PSCs for the first time, with downshifting property. We fabricate methylammonium lead triiodide (MAPbI 3 ) perovskite on a thin layer of CdSe/ZnS QDs ETL using evaporation technique. We find that the PSC on CdSe/ZnS QDs ETL with green emission gives us the best efficiency due to more suitable band alignment with respect to the perovskite film than the dots with red emission. We finally achieve a PSC with 18% PCE, indicating a superior UV stability and low hysteresis.Here, we considered CdSe/ZnS QDs (Mesolight) with green (520 nm) and red (640 nm) emissions at ETLs in the PSCs, which have photoluminescence quantum efficiencies (PLQEs) of 85% ( Figure S1, Supporting Information). Here, we used CdSe QDs wrapped by ZnS shell due to having higher PLQE and better downshifting property as compared with the pure QDs layers. [43] The PLQE has an important role in the efficiency of the device and if it is not high enough, the QDs layer cannot efficiently convert the photons with high energy to the photons with low energy, resulting in lower current density and thus PCE. In this work, we used a solid-state ligand exchange method for deposition of the QDs layer. Then, we used methylammonium triiodide (MAPbI 3 ) perovskit...

Enhancement of Schottky Junction Silicon Solar Cell with CdSe/ZnS Quantum Dots Decorated Metal Nanostructures

“…Compared to other CdSe QDs, the green one has a greater band gap, leading to a lower recombination rate in solar cells. Thus, CdSe/ZnS (green) is an potential candidate for enhancing PV performance [30,31].…”

Ultraviolet Photocatalytic Degradation of Perovskite Solar Cells: Progress, Challenges, and Strategies

“…Similarly, CdSe/ZnS QDs (PLQE of 85%) with green emission were proposed as ETLs for the first time. [ 118 ] However, it needs a vacuum technique for perovskite film deposition to prevent the solvent to dissolve the underneath QD layer.…”

Downconversion Materials for Perovskite Solar Cells

“…Apart from the efficiency improvement, these QDs have shown improved PSC stability under continuous illumination of light and under UV light. Tavakoli et al [ 160 ] reported the first incorporation of CdSe/ZnS core–shell QDs of green and red emissions as an ETL and DC dual layer. The measured PLQE was 85% for these QDs and showed how efficient it is at converting high‐energy photons to low‐energy photons.…”

“…e) The normalized PCE of TiO 2 and QD (green) devices under UV light. Reproduced with permission [160]. Copyright 2020, Wiley-VCH.…”