Perovskite solar cells (PSCs) have recently demonstrated a rapid power conversion efficiency of above 25%. In terms of physical properties, SnO2 is similar to TiO2 but with stronger charge extraction at the interface. Furthermore, the SnO2 electron transporting layer (ETL) is prepared using new, simple, and efficient methods, resulting in high-performance PSCs. This review initially described recent progress in SnO2 nanostructures and preparation methods. The passivation options were then divided into elemental doping, bilayer alterations, and interfacial modifications. Finally, we discussed the challenges and limitations of SnO2 ETL-based PSCs and made recommendations for further research.

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Advances in SnO2-based perovskite solar cells: from preparation to photovoltaic applications

Organohalide lead perovskites (PVKs) are among the leading materials for the fabrication of high-efficiency and low-cost photovoltaic devices. Deposition of a suitable electron transport layer (ETL) plays a pivotal role in the manufacturing of perovskite solar cells (PSCs). Among all reported ETLs, zinc oxide (ZnO) has not been developed properly compared with its counterparts such as TiO2 and SnO2. In this work, we fabricated PSCs based on low-temperature solution-processed ZnO nanoparticles under ambient conditions. The degradation of PVK films on the ZnO ETL has been widely reported in the literature. We demonstrate that the localization of positive ions resulting from hydroxyl groups (–OH) present at the ZnO surface is a reason for this issue. In order to deactivate these groups, we treated the surface of the ZnO ETL with carbon nanotubes (CNTs) before the deposition of the PVK film. We found that CNTs modify the ZnO surface and stop the potential reaction between the ZnO and PVK films. The results demonstrate that the CNT modification of ZnO resulted in a PVK film with larger grains without any pinholes. Upon incorporation of CNTs into our devices, we improved the power conversion efficiency of the PSC from 15.05% to 18.79%, possibly due to the higher quality of the PVK film and improved charge extraction properties. Most importantly, PSCs based on the ZnO/CNT ETL showed better ambient and thermal stability compared to the reference PSCs.

Surface treatment of ZnO films with carbon nanotubes for efficient and stable perovskite solar cells

Annealing Free Tin Oxide Electron Transport Layers for Flexible Perovskite Solar Cells

Hydrolysis-Regulated Chemical Bath Deposition of Tin-Oxide-Based Electron Transport Layers for Efficient Perovskite Solar Cells with a Reduced Potential Loss

To upscale the emerging perovskite photovoltaic technology to larger-size modules, industrially relevant deposition techniques need to be developed. In this work, the deposition of tin oxide used as an electron extraction layer is established using chemical bath deposition (CBD), a low-cost and solution-based fabrication process. Applying this simple low-temperature deposition method, highly homogeneous SnO2 films are obtained in a reproducible manner. Moreover, the perovskite layer is prepared by sequentially slot-die coating on top of the n-type contact. The symbiosis of these two industrially relevant deposition techniques allows for the growth of high-quality dense perovskite layers with large grains. The uniformity of the perovskite film is further confirmed by scanning electron microscopy (SEM)/scanning transmission electron microscopy (STEM) analysis coupled with energy dispersive X-ray spectroscopy (EDX) and cathodoluminescence measurements allowing us to probe the elemental composition at the nanoscale. Perovskite solar cells fabricated from CBD SnO2 and slot-die-coated perovskite show power conversion efficiencies up to 19.2%. Furthermore, mini-modules with an aperture area of 40 cm2 demonstrate efficiencies of 17% (18.1% on active area).

Industrially Compatible Fabrication Process of Perovskite-Based Mini-Modules Coupling Sequential Slot-Die Coating and Chemical Bath Deposition.

Planar perovskite solar cells (PSCs) incorporating n-type SnO2 have attracted significant interest because of their excellent photovoltaic performance. However, the film fabrication of SnO2 is limited by self-aggregation and inhomogeneous growth of the intermediate phase, which produces poor morphology and properties. In this study, a self-controlled SnO2 layer is fabricated directly on a fluorine-doped tin oxide (FTO) surface through simple and rapid chemical bath deposition. The PSCs based on this hydrolyzed SnO2 layer exhibit an excellent power conversion efficiency of 20.21 % with negligible hysteresis. Analysis of the electrochemical impedance spectroscopy on the charge transport dynamics indicates that the bias voltage influences both interfacial charge transportation and the ionic double layer under illumination. The hydrolyzed SnO2 -based PSCs demonstrate a faster ionic charge response time of 2.5 ms in comparison with 100.5 ms for the hydrolyzed TiO2 -based hysteretic PSCs. The results of quasi-steady-state carrier transportation indicate that a dynamic hysteresis in the J-V curves can be explained by complex ionic-electronic kinetics owing to the slow ionic charge redistribution and hole accumulation caused by electrode polarization, which causes an increase in charge recombination. This study reveals that SnO2 -based PSCs lead to a stabilized dark depolarization process compared with TiO2 -based PSCs, which is relevant to the charge transport dynamics in the high-performing planar SnO2 -based PSCs.

Self-Aggregation-Controlled Rapid Chemical Bath Deposition of SnO2 Layers and Stable Dark Depolarization Process for Highly Efficient Planar Perovskite Solar Cells.

Taemin Kim

Papers

Hydrolysis-Regulated Chemical Bath Deposition of Tin-Oxide-Based Electron Transport Layers for Efficient Perovskite Solar Cells with a Reduced Potential Loss

Self-Aggregation-Controlled Rapid Chemical Bath Deposition of SnO2 Layers and Stable Dark Depolarization Process for Highly Efficient Planar Perovskite Solar Cells.