Faming Li (李发明)

Surface post-treatment using larger organic spacer cations is widely recognized as one of the most effective approaches to suppress the defects and reconstruct microstructures in perovskite films. However, larger organic spacer cations always cause structural transformation to an uncontrollable low-dimensional phase at the perovskite surface, significantly restricting charge transport across interfaces within perovskite solar cells (PSCs). In this study, we introduce a bi-molecular competitive adsorption strategy using phenylmethylammonium iodide (PMAI) and octylammonium iodide (OAI) as co-modifiers from molecular dynamics perspectives. It is revealed that OA+ preferentially adsorbs on the surface of perovskite films owing to its much greater molecular polarity and steric hindrance effects, thereby inhibiting PMA+-induced surface layer transformation into a low-dimensional structural phase. This strategy therefore …

The performance of perovskite solar cells with inverted polarity (p-i-n) is still limited by recombination at their electron extraction interface, which also lowers the power conversion efficiency (PCE) of p-i-n perovskite-silicon tandem solar cells. A MgFx interlayer with thickness of ~1 nanometer at the perovskite/C60 interface favorably adjusts the surface energy of the perovskite layer through thermal evaporation, which facilitates efficient electron extraction and displaces C60 from the perovskite surface to mitigate nonradiative recombination. These effects enable a champion open-circuit voltage of 1.92 volts, an improved fill factor of 80.7%, and an independently certified stabilized PCE of 29.3% for a monolithic perovskite-silicon tandem solar cell ~1 square centimeter in area. The tandem retained ~95% of its initial performance after damp-heat testing (85°C at 85% relative humidity) for >1000 hours.

To date, the improvement of open‐circuit voltage (VOC) offers a breakthrough for the performance of perovskite solar cells (PSCs) toward their theoretical limit. Surface modification through organic ammonium halide salts (e.g., phenethylammonium ions PEA+ and phenmethylammonium ions PMA+) is one of the most straightforward strategies to suppress defect density, thereby leading to improved VOC. However, the mechanism underlying the high voltage remains unclear. Here, polar molecular PMA+ is applied at the interface between perovskite and hole transporting layer and a remarkably high VOC of 1.175 V is obtained which corresponds to an increase of over 100 mV in comparison to the control device. It is revealed that the equivalent passivation effect of surface dipole effectively improves the splitting of the hole quasi‐Fermi level. Ultimately the combined effect of defect suppression and surface dipole …

The photovoltaic (PV) performance of perovskite solar cells (PSCs) has rapidly advanced in the recent years; yet, the stability issue remains one of the last‐mile challenges on the road to commercialization. Charge transport layers and their interfaces with perovskites stand for critical tuning knobs that determine the device stability of PSCs. This review focuses on the effects of modification of SnO2 electron transport layers (ETLs) on the interfacial physicochemical properties and stability of PSC devices. In detail, the intrinsic defects, surface hydroxyls, and nonuniform morphology of SnO2 will negatively impact its interfacial physicochemical properties, thus degrading the device stability of PSCs. To tackle these existing issues, three modification approaches, such as surface morphology control, surface physicochemical modifications, and surface composite‐structure design, are categorized. Lastly, future perspectives …

NiOx-based perovskite solar cells (PSCs) have attracted much attention because of their low fabrication temperature, suppressed hysteresis, and superior stability. However, the poor interfacial contacts between NiOx and perovskite layers always limit the progress of PSCs. Here, we applied 2-thiophenemethylamine (TPMA) as charge transport channels at the interface between NiOx and perovskite layers. The introduction of TPMA provides moderate dipole moment pointing to the perovskite side and effectively promotes the charge transportation. Meanwhile, TPMA anchorage also passivates the defect states at the surfaces of both NiOx and MAPbI3, which compensates the voltage loss due to the change in NiOx work function induced by the dipole. Thus, the device performance has been significantly enhanced in both electrochemical properties and power conversion efficiency. Our work has demonstrated a new …

During the past decade, metal halide perovskites are widely studied in the field of optoelectronic materials due to their unique optical and electrical properties. Lead‐based halide perovskite solar cells (PSCs), in particular, currently achieve a record efficiency of 25.5%, thus showing strong potential in industrial application. However, toxicity of lead‐based perovskite materials possesses great concerns to natural environment and human body. Therefore, the quest for nontoxic and eco‐friendly elements to replace lead in perovskites is of great interest. Among all the element choices, tin(II) (Sn2+) is the most promising candidate. As a rising star of lead‐free PSCs, Sn‐based PSCs have drawn much attention and made promising progress during the past few years. While the rapid oxidation and decomposition of Sn‐based perovskites result in poor stability and low efficiency of PSCs. In this review, structural …

Perovskite/silicon tandem solar cells are promising avenues for achieving high‐performance photovoltaics with low costs. However, the highest certified efficiency of perovskite/silicon tandem devices based on economically matured silicon heterojunction technology (SHJ) with fully textured wafer is only 25.2% due to incompatibility between the limitation of fabrication technology which is not compatible with the production‐line silicon wafer. Here, a molecular‐level nanotechnology is developed by designing NiOx/2PACz ([2‐(9H‐carbazol‐9‐yl) ethyl]phosphonic acid) as an ultrathin hybrid hole transport layer (HTL) above indium tin oxide (ITO) recombination junction, to serve as a vital pivot for achieving a conformal deposition of high‐quality perovskite layer on top. The NiOx interlayer facilitates a uniform self‐assembly of 2PACz molecules onto the fully textured surface, thus avoiding direct contact between ITO and …

Inorganic CsPbI3 perovskite shows great potential in the field of photovoltaics due to its chemical and thermal stability. High-temperature (>320 °C) annealing is required to achieve the photoactive perovskite phase of CsPbI3, which, however, is not compatible with applications on thermally vulnerable substrates, such as silicon wafers and organics. Although approaches adopting HI effectively reduce the formation temperature of perovskite-phase CsPbI3, dimethylamine hydroiodide (DMAI) is inevitably formed as a thermally resilient byproduct that is hard to remove, which causes film heterogeneity, interfacial energy mismatch, and a negatively impacted device performance. Here, we develop a low-temperature strategy for the removal of DMAI to give efficient CsPbI3 perovskite solar cells (PSCs). We demonstrate that 2-thiophenylboric acid molecules will undergo a condensation reaction at a low post-annealing …

Halide perovskites have shown superior potentials in flexible photovoltaics due to their soft and high power‐to‐weight nature. However, interfacial residual stress and lattice mismatch due to the large deformation of flexible substrates have greatly limited the performance of flexible perovskite solar cells (F‐PSCs). Here, ammonium formate (HCOONH4) is used as a pre‐buried additive in electron transport layer (ETL) to realize a bottom‐up infiltration process for an in situ, integral modification of ETL, perovskite layer, and their interface. The HCOONH4 treatment leads to an enhanced electron extraction in ETL, relaxed residual strain and micro‐strain in perovskite film, along with reduced defect densities within these layers. As a result, a top power conversion efficiency of 22.37% and a certified 21.9% on F‐PSCs are achieved, representing the highest performance reported so far. This work links the critical connection …

The prevailing perovskite solar cells (PSCs) employ hybrid organic–inorganic halide perovskites as light absorbers, but these materials exhibit relatively poor environmental stability, which potentially hinders the practical deployment of PSCs. One important strategy to address this issue is replacing the volatile and hygroscopic organic cations with inorganic cesium cations in the crystal structure, forming all-inorganic halide perovskites. In this context, CsPbI3 perovskite is drawing phenomenal attention, primarily because it exhibits an ideal bandgap of 1.7 eV for the use in tandem solar cells, and it shows significantly enhanced thermal stability that is the key to the long-term device operation. Within only half a decade, the power conversion efficiency (PCE) of CsPbI3 PSCs has ramped beyond 20%, which has been driven by inventions of numerous processing methods for high-quality CsPbI3 perovskite thin films …

In most perovskite nanocrystal (PeNC)-based optoelectronic and photonic applications, surface ligands inevitably lead to a donor–bridge–acceptor charge transfer configuration. In this article, we demonstrate successful modulation of electron transfer (ET) rates from all-inorganic CsPbBr3 PeNCs to mesoporous titanium dioxide films, by using different surface ligands including single alkyl chain oleic acid and oleylamine, cross-linked insulating (3-aminopropyl)triethoxysilane and aromatic naphthoic acid molecules as the ligand-bridge. We systematically investigated the ET process through time-resolved photoluminescence spectroscopy. Calculations verified the ligand-bridge barrier effect of the three species upon the ET process. Transient absorption measurements excluded carrier-delocalization effect of the naphthoic acid ligands and confirmed the bridge-barrier effect. Our work provides a perspective for …

Vapor-deposited CsPbI3 solar cells demonstrate an efficiency of 16 Vapor-deposited CsPbI 3 solar cells demonstrate an efficiency of 16 Sci Bull (Beijing). 2021 Apr 30;66(8):757-760. doi: 10.1016/j.scib.2020.12.024. Epub 2020 Dec 30. Authors Qingrong Huang 1 , Faming Li 1 , Ming Wang 1 , Yong Xiang 2 , Liming Ding 3 , Mingzhen Liu 4 Affiliations 1 School of Materials and Energy, University of Electronic Science and Technology of China, Chengdu 611731, China; Center for Applied Chemistry, University of Electronic Science and Technology of China, Chengdu 611731, China. 2 School of Materials and Energy, University of Electronic Science and Technology of China, Chengdu 611731, China. Electronic address: xiang@uestc.edu.cn. 3 Center for Excellence in Nanoscience (CAS), Key Laboratory of Nanosystem and Hierarchical Fabrication (CAS), National Center for Nanoscience and Technology, Beijing …

Organic small molecule material, spiro-OMeTAD, is widely used in perovskite solar cells as the hole transport material due to its desirable properties, such as suitable highest occupied molecular orbital energy levels, high solubility and good film forming ability. However, the aggregation and hydrolysis of the common additive, Li-TFSI, in the spiro-OMeTAD, lead to the existence of voids/pinholes in the hole transport layer, which limits further improvement of perovskite solar cell efficiency. Here, we develop a low-cost and easy-fabrication technique to substantially reduce the undesired voids in hole transport layer by modifying it with commercially available PbI2. The strong interaction between the PbI2 and the TBP retards the evaporation of TBP, which hinders the agglomeration of Li-TFSI and generation of voids in the HTL. Consequently, the HTL shows a dramatically improved mobility and efficiency of charge …

Usage of nonhalide lead sources for fabricating perovskite solar cells (PSCs) has recently attracted increasing attention as a promising route toward realizing high quality PSC devices. However, the unique role of nonhalide lead sources in improving perovskite film morphology and PSC performance has largely remained unexplored, impeding broader application of these materials. Here, it is demonstrated that by using a new nonhalide lead source, lead formate (Pb(HCOO)2), good control of perovskite film morphology can be achieved. With the usage of lead formate, PbI2 can nicely border the perovskite grain boundaries (GBs) and form domain “walls” that segregate the individual perovskite crystal domains. The PbI2 at the GBs lead to significant improvement in film quality and device performance through passivating the defects at the perovskite GBs and suppressing lateral carrier diffusion. An impressive …

CdSe single crystals (SCs), with a relatively high atomic number, large X-ray absorption coefficients, and high carrier mobility, are expected to provide high-performance detection for X-ray. However, the difficulty of growing high-quality CdSe SC has severely limited its application in X-ray detection. In this work, we develop an unconstrained physical gas phase method and in situ annealing process to grow high-quality CdSe SCs under unconstrained conditions. Using this method, CdSe SCs exhibit natural exposure planes, ultrahigh resistivity of 5.43 × 1012 to 1.29 × 1013 Ω cm and high μτ product of 1.3 × 10–2 to 1.5 × 10–2 cm2 V–1. It is also observed that CdSe SC X-ray detectors exhibit a record sensitivity of 2.08 × 105 μC Gyair–1 cm–2 and a low detection limit of 85 nGyair s–1, which are both desired in medical diagnostics. Moreover, those devices with different crystal directions provide anisotropic X-ray …

Organic–inorganic lead halide perovskites have attracted great interest as low-cost and high efficiency solar cells. However, the excessive surface defects of perovskite crystal grains are still a crucial factor that limits further improvement in the performance of corresponding devices. Here, we introduce potassium chloride (KCl) into the precursor of a triple A-cation mixed-halide perovskite to passivate the surface defects and provide an insight into the underlying passivation mechanism of this common salt. We reveal that KCl exists on the surface of perovskite grains, suppressing the grain surface defects and modulating the energy level alignment of the perovskite solar cell (PSC). KCl added PSCs achieved a high open circuit voltage of 1.162 V compared with that of a control device (1.087 V), due to suppressed nonradiative recombination losses. Our work investigates the synergetic effect of K+ and Cl− on the …

Two-dimensional (2D) Sn-based lead-free perovskites have attracted extensive attention because of their nontoxicity and wide light absorption. It has been proven that the introduced organic spacer cations in the perovskite crystal prevent Sn2+ from oxidation to Sn4+. However, the effects of the alkyl chain length of these cations on the perovskite properties are unclear. Here, we investigate the impacts of chain length on crystal orientation and phase distribution of 2D Sn-based perovskite films by employing different alkylamines spacer cations (butylamine, octylamine, and dodecylamine). With the increase of alkyl chain length, the phase distribution of 2D Sn-based perovskite crystals become disordered and less oriented. Therefore, benefiting from application of a short alkyl chain in the organic spacer cation (e.g., BA), we manage to retard the oxidation process of Sn2+ for better device performance. Our work …

Flexible solar cells have attracted increasingly attentions due to its possible extensive applications in wearable, portable, flyable and deployable devices. The fabrication of flexible perovskite solar cells (PSCs) strictly requires the fabrication temperature below 150 °C due to the limitation of flexible substrate. For retaining the process at low temperature, applying anti-solvents has becoming to the most popular method. However, the involvement of anti-solvents requires very precise control and brings toxicity in the fabrication procedures, which limits its large-scale industrial use. Here, we propose a strategy that simply replacing the usual anti-solvents with CH3NH3Br (CH3NH3+, MA) into dynamic spinning of perovskite precursor significantly reduces the formation energy of α-phase FA-perovskites to 40 °C. An optimized annealing temperature at 100 °C provides high-quality morphology and crystallization of FA …