Search

Tin (Sn)-based perovskites are very promising for the fabrication of low-toxicity lead-free perovskite solar cells (PSCs), but they suffer from easy oxidation of Sn2+ to Sn4+ which leads to poor performance.

In recent years, hybrid organic–inorganic halide perovskite solar cells (PVSCs) have emerged as leading candidates for next-generation photovoltaic technologies. The architecture of PVSCs rely on charge transport layers to enable optimal efficiency and stability. In particular, tin oxide (SnO2) has been shown to be an effective electron transport layer (ETL) due to favorable energy level alignment, relatively wide band gap, and high environmental and thermal stability. However, traditional processing of SnO2 necessitates a high-temperature and/or long-duration sintering step that limits substrate choice and introduces manufacturing challenges. To overcome this limitation, we present here a rapid, low-temperature, solution-based method for SnO2 film fabrication based on intense pulsed photonic annealing. Following a comprehensive survey of the precursor solution and photonic annealing conditions, light exposure as short as 20 milliseconds is shown to provide a high-quality nanocrystalline SnO2 film at room temperature, enabling PVSCs with low hysteresis and high power conversion efficiencies exceeding 15%. Overall, this work establishes a processing pathway for SnO2-based PVSCs that is compatible with flexible substrates and high-throughput, roll-to-roll manufacturing.

Both tin oxide (SnO2) and fullerenes have been reported as electron selective layers (ESLs) for producing efficient lead halide perovskite solar cells. Here, we report that SnO2 and fullerenes can work cooperatively to further boost the performance of perovskite solar cells. We find that fullerenes can be redissolved during perovskite deposition, allowing ultra-thin fullerenes to be retained at the interface and some dissolved fullerenes infiltrate into perovskite grain boundaries. The SnO2 layer blocks holes effectively; whereas, the fullerenes promote electron transfer and passivate both the SnO2/perovskite interface and perovskite grain boundaries. With careful device optimization, the best-performing planar perovskite solar cell using a fullerene passivated SnO2 ESL has achieved a steady-state efficiency of 17.75% and a power conversion efficiency of 19.12% with an open circuit voltage of 1.12 V, a short-circuit current density of 22.61 mA cm−2, and a fill factor of 75.8% when measured under reverse voltage scanning. We find that the partial dissolving of fullerenes during perovskite deposition is the key for fabricating high-performance perovskite solar cells based on metal oxide/fullerene ESLs.

Mg doping into high temperature processed (HTP) SnO2 as an electron selective layer (ESL) significantly improves perovskite solar cell (PSC) performance including power conversion efficiency (PCE), open circuit voltage, short circuit current (JSC) and fill factor. An optimum Mg content (7.5%) affords a uniform, smooth and dense Mg-doped SnO2 film with high electron mobility and its corresponding PSC displays less hysteresis and achieves a highest steady-state PCE of 14.55%, nearly 92.8% enhancement compared to that with undoped SnO2. Electrical measurements show that suitable Mg doping dramatically reduces free electron density and substantially increases the electron mobility of pristine SnO2. The mechanism of efficiency enhancement for PSCs is proposed as follows: the low free electron density causes suppression of carrier recombination and high electron mobility facilitates fast extraction of electrons from perovskite to ESLs, contributing to an improved JSC. Impedance analysis strongly supports the proposed mechanism and reveals that the higher is the electron mobility, the higher is the electron collection efficiency, and the higher are the JSC and PCE. The HTP SnO2 with a suitable Mg content can be an excellent ESL for PSCs and might well be a suitable candidate of ESLs for CdTe, CuInGaSe and other photovoltaic devices involved in HTP treatment.

Thin-film photovoltaics based on organic–inorganic hybrid perovskite light absorbers have recently emerged as a promising low-cost solar energy harvesting technology. Over the past several years, we have witnessed a great and unexpected progress in organic–inorganic perovskite solar cells (PSCs). The power conversion efficiency (PCE) increased from 3.8% to 20.1% and exceeded the highest efficiency of conventional dye-sensitized solar cells. Here, the focus is specifically on the recent developments of the electron transport layer (ETL) in PSCs, which is an important part for high performing PSCs. This review briefly discusses the development of the structure of PSCs, and we attempt to give a systematic introduction about the optimization of ETL and its related interfaces for efficient PSCs. Moreover, the introduction of appropriate interfacial materials is another important issue to improve PSC performance by optimizing the interfacial electronic properties between the perovskite layer and the charge-collecting electrode. Besides, some related issues such as device stability and hysteresis behavior are also discussed here.

Efficient lead halide perovskite solar cells have been realized using SnO2 as electron selective layers (ESLs). Here, we report on the effects of the annealing temperature of solution-processed SnO2 ESLs on the performance of perovskite solar cells. We find that the cells using low-temperature annealed SnO2 (LT-SnO2) ESLs outperform the cells using high-temperature annealed SnO2 (HT-SnO2) ESLs, exhibiting higher open circuit voltages and fill factors. Structural, electrical, optical, and electrochemical characterizations reveal the origin of the performance differences: LT-SnO2 produces better film coverage, wider band gap, and lower electron density than that of HT-SnO2. The confluence of these properties results in more effective transportation of electrons and blocking of holes, leading to lower interface recombination. Therefore, LT-SnO2 ESLs are preferred for manufacturing perovskite solar cells on flexible substrates.

Efficient organic–inorganic lead halide perovskite solar cells with regular structure typically use solution-processed electron selective layers. Here, we demonstrated efficient planar perovskite solar cells using vacuum-processed C60 compact electron selective layers at room temperature. The best-performing planar perovskite solar cell has shown a power conversion efficiency of 15.14% with an open circuit voltage of 1.08 V and a fill factor of 74.51% measured under reverse voltage scanning. Our results suggest that vacuum-processed fullerene electron selective layer is a good candidate for fabricating all perovskite tandem solar cells.

Efficient organic solar cells (OSCs) based on regioregular poly(3-hexylthiophene):fullerene derivative [6,6]-phenyl-C61butyric acid methyl ester composites have been fabricated on fluorine-doped tin oxide (FTO) coated glass substrates by a radio frequency (RF) sputtered and ultraviolet ozone (UVO) treated MoS2 film as the hole-transport layer (HTL). With the help of X-ray photoelectron spectroscopy, ultraviolet photoelectron spectroscopy, Raman spectroscopy, transmission spectra and the Hall-effect system, we find that the deposition temperature can modulate the contents of the various valence states of molybdenum, which can result in changes of the energy level, and the optical and electrical properties of the MoS2 films. MoS2 has been oxidized to a double-layered MoO3–MoS2 film by UVO treatment. Due to the presence of the molybdenum oxidation states Mo5+ and Mo6+, the MoS2 film shows p-type conductive behavior, and its smaller electron affinity can effectively block electron from exciton dissociation. By optimizing the HTL thickness and sputtering deposition temperature, a power conversion efficiency up to 4.15% has been achieved for an OSC that used a double-layered MoO3–MoS2 film as the HTL. Its JSC is bigger than that of the OSC with a pure MoO3 film as the HTL. This shows that this double layer MoO3–MoS2 interface is more favorable for hole-transfer.