Textured Perovskite/Silicon Tandem Solar Cells Achieving Over 30% Efficiency Promoted by 4-Fluorobenzylamine Hydroiodide.

Monolithic textured perovskite/silicon tandem solar cells (TSCs) are expected to achieve maximum light capture at the lowest cost, potentially exhibiting the best power conversion efficiency. However, it is challenging to fabricate high-quality perovskite films and preferred crystal orientation on commercially textured silicon substrates with micrometer-size pyramids. Here, we introduced a bulky organic molecule (4-fluorobenzylamine hydroiodide (F-PMAI)) as a perovskite additive. It is found that F-PMAI can retard the crystallization process of perovskite film through hydrogen bond interaction between F- and FA+ and reduce (111) facet surface energy due to enhanced adsorption energy of F-PMAI on the (111) facet. Besides, the bulky molecular is extruded to the bottom and top of perovskite film after crystal growth, which can passivate interface defects through strong interaction between F-PMA+ and undercoordinated Pb2+/I-. As a result, the additive facilitates the formation of large perovskite grains and (111) preferred orientation with a reduced trap-state density, thereby promoting charge carrier transportation, and enhancing device performance and stability. The perovskite/silicon TSCs achieved a champion efficiency of 30.05% based on a silicon thin film tunneling junction. In addition, the devices exhibit excellent long-term thermal and light stability without encapsulation. This work provides an effective strategy for achieving efficient and stable TSCs.

Diffusible Capping Layer Enabled Homogeneous Crystallization and Component Distribution of Hybrid Sequential Deposited Perovskite.

Nowadays, the development of wide-bandgap perovskite by thermal evaporation and spin-coating hybrid sequential deposition (HSD) method has special meaning on textured perovskite/silicon tandem solar cells. However, the common issues of insufficient reaction caused by blocking of perovskite capping layer are exacerbated in HSD, because evaporated precursors are usually denser with higher crystallinity and the widely used additive-assisted microstructure is also difficult to access. Here, a facile "diffusible perovskite capping layer" (DPCL) strategy to solve this dilemma is presented. With DPCL, crystallization alleviation of perovskite and more diffusion channels of organic salts can be realized simultaneously, contributing to a homogenization process. The resultant perovskite films exhibit complete conversion, uniform crystallization, enhanced quality, and reduced defect, leading to obvious improvements in device efficiency, repeatability, and stability. This work offers a way to promote the development of textured tandems a step further.

Improving the performance of inorganic perovskite solar cells via the perovskite quantum dot dynamically mediated film growth method.

Perovskite quantum dots (PQDs) are promising interface modification materials for perovskite solar cells (PSCs). However, due to the limitation of the preparation method, it is hard to use PQDs as substrates for the growth of perovskite films by the common solution process. In this work, by introducing the rare earth element Ce into PQDs with the vacuum freezing and drying technology, we have successfully improved the solvent stability of PQDs. Moreover, we propose a technology, PQD dynamically mediated growth of perovskite film (PDMG), to prepare high-quality perovskite films, which can avoid the formation of PQD charge-blocking layers. Thanks to the improvement of perovskite crystallinity and the charge transport ability, the PCE is improved from 10.44% to 12.14% for CsPbI2Br PSCs and from 14.43% to 16.38% for CsPbI3 PSCs. Our work opens an avenue for using PQDs as substrates in the fabrication of highly efficient PSCs.

2D Perovsktie Substrate-Assisted CsPbI3 Film Growth for High-Efficiency Solar Cells.

High-quality perovskite films are beneficial for fabricating perovskite solar cells (PSCs) with excellent photoelectric performance. The substrate on which the perovskite film grows plays a profound role in improving the crystallization quality of the perovskite film. Here, we proposed a novel method for optimizing CsPbI3 perovskite films, that is, two-dimensional (2D) perovskite substrate-assisted growth (2D-PSAG) method. The prepared PEA2PbI4 2D perovskite with proper wettability and roughness is used as a substrate to fabricate the high-quality CsPbI3 film. Moreover, it is found that PEA cations show a vertical gradient distribution within the whole CsPbI3 film because of their bottom-up self-diffusion. Also, PEA cations induce the moderate distortion of [PbI6]4- octahedron and slight lattice contraction of CsPbI3 by chemically bonding between Pb and N atoms. Surprisingly, the trace amounts of PEA cations lead to a bottom-up gradient phase transition from γ-CsPbI3 to ß-CsPbI3. Therefore, the energy-level alignment becomes more matched at the interface of the perovskite layer/hole transport layer (poly3-hexylthiophene, P3HT), which denotes a large improvement of hole transport and extraction in PSCs made with the 2D-PSAG method. As a result, the CsPbI3-based PSCs with P3HT as a hole transport layer exhibit a champion efficiency of 17.13%, while the control device exhibits a PCE of only 14.16%. The PSCs made by the 2D-PSAG method retain above 70% of the initial PCE value after storage of 9 days in air (RH 10-20%), while the control device decomposes completely after 9 days. The improved stability could originate from the steric effects of PEA cations and the high crystallization quality of the mixed-phase CsPbI3 film. Therefore, 2D-PSAG is a novel and promising strategy to develop all-inorganic PSCs with high performance and stability.

Application of quantum dots in perovskite solar cells.

Perovskite solar cells (PSCs) are important candidates for next-generation thin-film photovoltaic technology due to their superior performance in energy harvesting. At present, their photoelectric conversion efficiencies (PCEs) are comparable to those of silicon-based solar cells. PSCs usually have a multi-layer structure. Therefore, they face the problem that the energy levels between adjacent layers often mismatch each other. Meanwhile, large numbers of defects are often introduced due to the solution preparation procedures. Furthermore, the perovskite is prone to degradation under ultraviolet (UV) irradiation. These problems could degrade the efficiency and stability of PSCs. In order to solve these problems, quantum dots (QDs), a kind of low-dimensional semiconductor material, have been recently introduced into PSCs as charge transport materials, interfacial modification materials, dopants and luminescent down-shifting materials. By these strategies, the energy alignment and interfacial conditions are improved, the defects are efficiently passivated, and the instability of perovskite under UV irradiation is suppressed. So the device efficiency and stability are both improved. In this paper, we overview the recent progress of QDs' utilizations in PSCs.