Quantum and dielectric confinement effects in Ruddlesden-Popper 2D hybrid perovskites create excitons with a binding energy exceeding 150 meV. We exploit the large exciton binding energy to study exciton and carrier dynamics as well as electron-phonon coupling (EPC) in hybrid perovskites using absorption and photoluminescence (PL) spectroscopies. At temperatures <75 K, we resolve splitting of the excitonic absorption and PL into multiple regularly spaced resonances every 40-46 meV, consistent with EPC to phonons located on the organic cation. We also resolve resonances with a 14 meV spacing, in accord with coupling to phonons with mixed organic and inorganic character. These assignments are supported by density-functional theory calculations. Hot exciton PL and time-resolved PL measurements show that vibrational relaxation occurs on a picosecond time scale competitive with that for PL. At temperatures >75 K, excitonic absorption and PL exhibit homogeneous broadening. While absorption remains homogeneous, PL becomes inhomogeneous at temperatures <75K, which we speculate is caused by the formation and subsequent dynamics of a polaronic exciton.

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Direct Observation of Electron--Phonon Coupling and Slow Vibrational Relaxation in Organic--Inorganic Hybrid Perovskites

Perovskite solar cells (PSCs) based on the regular n–i–p device architecture have reached above 25% certified efficiency with continuously reported improvements in recent years. A key common factor for these recent breakthroughs is the development of SnO2 as an effective electron transport layer in these devices. In this article, the key advances in SnO2 development are reviewed, including various deposition approaches and surface treatment strategies, to enhance the bulk and interface properties of SnO2 for highly efficient and stable n–i–p PSCs. In addition, the general materials chemistry associated with SnO2 along with the corresponding materials challenges and improvement strategies are discussed, focusing on defects, intrinsic properties, and impact on device characteristics. Finally, some SnO2 implementations related to scalable processes and flexible devices are highlighted, and perspectives on the future development of efficient and stable large‐scale perovskite solar modules are also provided.

Advances in SnO2 for Efficient and Stable n–i–p Perovskite Solar Cells

Tin dioxide (SnO2), the most stable oxide of tin, is a metal oxide semiconductor that finds its use in a number of applications due to its interesting energy band gap that is easily tunable by doping with foreign elements or by nanostructured design such as thin film, nanowire or nanoparticle formation, etc., and its excellent thermal, mechanical and chemical stability. In particular, its earth abundance and non-toxicity make it very attractive for use in a number of technologies for sustainable development such as energy harvesting and storage. This article attempts to review the state of the art of synthesis and properties of SnO2, focusing primarily on its application as a transparent conductive oxide (TCO) in various optoelectronic devices and second in energy harvesting and energy storage devices where it finds its use as an electron transport layer (ETL) and an electrode material, respectively. In doing so, we discuss how tin oxide meets the requirements for the above applications, the challenges associated with these applications, and how its performance can be further improved by adopting various strategies such as doping with foreign metals, functionalization with plasma, etc. The article begins with a review on the various experimental approaches to doping of SnO2 with foreign elements for its enhanced performance as a TCO as well as related computational studies. Herein, we also compare the TCO performance of doped tin oxide as a function of dopants such as fluorine (F), antimony (Sb), tantalum (Ta), tungsten (W), molybdenum (Mo), phosphorus (P), and gallium (Ga). We also discuss the properties of multilayer SnO2/metal/SnO2 structures with respect to TCO performance. Next, we review the status of tin oxide as a TCO and an ETL in devices such as organic light emitting diodes (OLEDs), organic photovoltaics (OPV), and perovskite solar cells (including plasma treatment approaches) followed by its use in building integrated photovoltaic (BIPV) applications. Next, we review the impact of SnO2, mainly as an electrode material on energy storage devices starting from the most popular lithium (Li)-ion batteries to Li–sulfur batteries and finally to the rapidly emerging technology of supercapacitors. Finally, we also compare the performance of doped SnO2 with gallium (Ga) doped zinc oxide (ZnO), the main sustainable alternative to SnO2 as a TCO and summarize the impact of SnO2 on circular economies and discuss the main conclusions and future perspectives. It is expected that the review will serve as an authoritative reference for researchers and policy makers interested in finding out how SnO2 can contribute to the circular economy of some of the most desired sustainable and clean energy technologies including the detailed experimental methods of synthesis and strategies for performance enhancement.

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Tin oxide for optoelectronic, photovoltaic and energy storage devices: a review

The interfacial properties for the buried junctions of the perovskite solar cells (PSCs) play a crucial role for the further enhancement of the power conversion efficiency (PCE) and stability of devices. Delicate manipulation of the interface properties such as the defect density, energy alignment, perovskite film quality, etc., guarantees efficient extraction and transport of photogenerated carriers. Herein, chlorobenzenesulfonic potassium salts are presented as a novel multifunctional agent to modify the buried tin oxide (SnO2)/perovskite interface for regular PSCs. The increasing number of carbon‐chlorine bonds (CCl) in 2,4,5‐trichlorobenzenesulfonic potassium (3Cl‐BSAK) exhibit efficient interaction with uncoordinated Sn, effectively filling oxygen vacancies in the SnO2 surface. Importantly, synergistic effects of the functional group‐rich organic anions and the potassium ion are achieved for reduced defect density, carrier recombination, and hysteresis. A champion PCE of 24.27% and the open‐circuit voltage (VOC) up to 1.191 V for modified devices are obtained. The unencapsulated devices maintain 80% of their initial PCE after aging at 80 °C for 800 h in the atmosphere and 95% after aging for 100 d. With 3Cl‐BSAK decoration, a high efficiency semitransparent PSC with a PCE of 12.83% and an average visible light transmittance (AVT) over 27% is also obtained.

Chlorobenzenesulfonic Potassium Salts as the Efficient Multifunctional Passivator for the Buried Interface in Regular Perovskite Solar Cells

Modification of SnO2 Electron Transport Layer: Brilliant Strategies to Make Perovskite Solar Cells Stronger

Batch chemical bath deposition of large-area SnO2 film with mercaptosuccinic acid decoration for homogenized and efficient perovskite solar cells

The allure of high efficiency and low-temperature solution-processed organic-inorganic hybrid perovskite solar cells (PSCs) are inspiring scientists to seek for its commercialization. Interface passivation engineering has become an effective way to further enhance the efficiency and stability of PSCs by defect passivation, reduces the charge recombination and ion migration initiation and hysteresis control, etc. Herein, we have summarized the effects and recent research progress of interface passivation engineering in PSCs. Interface passivation layers can be realized by using the solution and/or vacuum evaporation processes which are very adaptable to varied materials with different properties and fabrication processes for enhanced photovoltaic performance and stability.

Interface passivation engineering for hybrid perovskite solar cells

A novel aqueous Sn-S complex solution was applied as precursor to fabricate SnO2 electron selective layers (ESLs) for the hybrid perovskite solar cells (PSCs). The tin and sulfur powder were directly dissolved in a (NH4)2S water solution to form Sn-S precursor. After depositon and annealing, the SnO2 film was formed, presenting as a low cost and enviromental friendly method for preparation of ESL. The films showed excellent transmittance at visible wavelength range. Moreover, the method exhibited high compatibility for doping using Cu, Cd, Li, and Zn elements. Zn doping (0.05 M) in the as-prepared SnO2 ESL significantly improved perovskite solar cells (PSCs) performance. The highest PCE of 13.17% was achived with 15% enhancement compared to that of undoped SnO2 ESL samples. TiCl4 modifications on SnO2 film improved photovoltaic performance to 14.45%, but resulted in the poor long-term stability, around 80% more degredation than that of PSCs based on Zn-doped SnO2 films.

Wenjian Shen

Papers

Batch chemical bath deposition of large-area SnO2 film with mercaptosuccinic acid decoration for homogenized and efficient perovskite solar cells

Interface passivation engineering for hybrid perovskite solar cells

Aqueous Sn-S Complex Derived Electron Selective Layer for Perovskite Solar Cells