All-inorganic perovskite solar cells (pero-SCs) are attracting considerable attention due to their promising thermal stability, but their inferior power-conversion efficiency (PCE) and moisture instability are hindering their application. Here, we used a gradient thermal annealing (GTA) method to control the growth of a-CsPbI 2 Br crystals and then utilized a green anti-solvent (ATS) isopropanol to further optimize the morphology of a-CsPbI 2 Br film. Through this GTA-ATS synergetic effect, the growth of a-CsPbI 2 Br crystals could be precisely controlled, leading to a high-quality perovskite film with one-micron average grain size, low root-mean-square of 25.9 nm, and reduced defect density. Pero-SCs based on this CsPbI 2 Br film achieved a champion scan PCE of 16.07% (stabilized efficiency of 15.75%), which is the highest efficiency reported in all-inorganic pero-SCs. Moreover, the CsPbI 2 Br pero-SC demonstrates excellent robustness against moisture and oxygen, and maintains 90% of initial PCE after aging 120 hr under 100 mW/cm 2 UV irradiation.
Organic solar cells (OSCs) can be unstable under ultraviolet (UV) irradiation. To address this issue and enhance the power conversion efficiency (PCE), an inorganic-perovskite/organic four-terminal tandem solar cell (TSC) based on a semitransparent inorganic CsPbBr perovskite solar cell (pero-SC) as the top cell and an OSC as bottom cell is constructed. The high-quality CsPbBr photoactive layer of the planar pero-SC is prepared with a dual-source vacuum coevaporation method, using stoichiometric precursors of CsBr and PbBr with a low evaporation rate. The resultant opaque planar pero-SC exhibits an ultrahigh open-circuit voltage of 1.44 V and the highest reported PCE of 7.78% for a CsPbBr -based planar pero-SC. Importantly, the devices show no degradation after 120 h UV light illumination. The related semitransparent pero-SC can almost completely filter UV light and well maintain photovoltaic performance; it additionally shows an extremely high average visible transmittance. When it is used to construct a TSC, the top pero-SC acting as a UV filter can utilize UV light for photoelectric conversion, avoiding the instability problem of UV light on the bottom OSC that can meet the industrial standards of UV-light stability for solar cells, and leading to the highest reported PCE of 14.03% for the inorganic-perovskite/organic TSC.
Bulk-heterojunction organic solar cells (OSCs) have received considerable attention with significant progress recently and offer a promising outlook for portable energy resources and building-integrated photovoltaics in the future. Now, it is urgent to promote the research of OSCs toward their commercialization. For the commercial application of OSCs, it is of great importance to develop high performance, high stability, and low cost photovoltaic materials. In this review, a comprehensive overview of the fundamental requirements of photoactive layer materials and interface layer materials toward commercialization is provided, mainly focusing on high performance, green manufacturing, simplifying device fabrication processes, stability, and cost issues. Furthermore, the perspectives and opportunities for this emerging field of materials science and engineering are also discussed.
Charged defects at the surface of the organic–inorganic perovskite active layer are detrimental to solar cells due to exacerbated charge carrier recombination. Here we show that charged surface defects can be benign after passivation and further exploited for reconfiguration of interfacial energy band structure. Based on the electrostatic interaction between oppositely charged ions, Lewis-acid-featured fullerene skeleton after iodide ionization (PCBB-3N-3I) not only efficiently passivates positively charged surface defects but also assembles on top of the perovskite active layer with preferred orientation. Consequently, PCBB-3N-3I with a strong molecular electric dipole forms a dipole interlayer to reconfigure interfacial energy band structure, leading to enhanced built-in potential and charge collection. As a result, inverted structure planar heterojunction perovskite solar cells exhibit the promising power conversion efficiency of 21.1% and robust ambient stability. This work opens up a new window to boost perovskite solar cells via rational exploitation of charged defects beyond passivation.
Polymer solar cells (PSCs) possess the unique features of semitransparency and coloration, which make them potential candidates for applications in aesthetic windows. Here, the authors fabricate inverted semitransparent PSCs with high-quality hybrid Au/Ag transparent top electrodes and finetuned dielectric mirrors (DMs). It is demonstrated that the device color can be tailored and the light harvesting in the PSCs can be enhanced by matching the bandgap of the polymer donors in the active layer with the specifically designed maximum-reflection-center-wavelengths of the DMs. A detailed chromaticity analysis of the semitransparent PSCs from both bottom and top (mirror) views is also carried out. Furthermore, the inverted semitransparent PSCs based on PTB7-Th:PC 71 BM with six pairs of DMs demonstrate a maximum power conversion efficiency (PCE) of 7.0% with an average visible transmittance (AVT) of 12.2%. This efficiency is one of the highest reported for semitransparent PSCs, corresponding to 81.4% of the PCE from opaque counterpart devices. The device design and processing method are also successfully adapted to a flexible substrate, resulting in a device with a competitive PCE of 6.4% with an AVT of 11.5%. To the best of our knowledge, this PCE value is the highest value reported for a flexible semitransparent PSC.
Tailoring the doping of semiconductors in heterojunction solar cells shows tremendous success in enhancing the performance of many types of inorganic solar cells, while it is found challenging in perovskite solar cells because of the difficulty in doping perovskites in a controllable way. Here, a small molecule of 4,4′,4″,4″′‐(pyrazine‐2,3,5,6‐tetrayl) tetrakis (N,N‐bis(4‐methoxyphenyl) aniline) (PT‐TPA) which can effectively p‐dope the surface of FAxMA1−xPbI3 (FA: HC(NH2)2; MA: CH3NH3) perovskite films is reported. The intermolecular charge transfer property of PT‐TPA forms a stabilized resonance structure to accept electrons from perovskites. The doping effect increases perovskite dark conductivity and carrier concentration by up to 4737 times. Computation shows that electrons in the first two layers of octahedral cages in perovskites are transferred to PT‐TPA. After applying PT‐TPA into perovskite solar cells, the doping‐induced band bending in perovskite effectively facilitates hole extraction to hole transport layer and expels electrons toward cathode side, which reduces the charge recombination there. The optimized devices demonstrate an increased photovoltage from 1.12 to 1.17 V and an efficiency of 23.4% from photocurrent scanning with a stabilized efficiency of 22.9%. The findings demonstrate that molecular doping is an effective route to control the interfacial charge recombination in perovskite solar cells which is in complimentary to broadly applied defect passivation techniques.
solution-processing opens an avenue toward flexibility, simple device fabrication, versatility of interface engineering, and feasibility of multijunction solar cells. [1,2] The rapidly developed planar p-i-n pero-SCs promote its power conversion efficiency (PCE) exceeding 21%. [3][4][5] Among the highperformance devices, [6,6]-phenyl-C 61 -butyric acid methyl ester (PCBM) is by far predominantly used for the electron transport layer (ETL) in planar p-i-n pero-SCs owing to its multifunctionality, including trap-states passivation and efficient electron extracting ability. [6][7][8] Nevertheless, some inferior properties, such as insufficient coverage on perovskite film, [9] energy disorder, [10] and ineffective passivation on the under-coordinated Pb 2+ ions defects of perovskite surface, [5] still hamper further enhancement of the PCE and stability of the PCBM-based pero-SCs.As for the conventional PCBM ETL grown on perovskite film, because of its discontinuous and aggregated nature, the water molecules in ambient atmosphere can easily permeate it then diffuse into the perovskite film. [9,11] This process is likely to form a hydrate perovskite phase that would accelerate the decomposition of CH 3 NH 3 PbI 3 (MAPbI 3 ) crystal lattice. [12] The resulting decomposition products, such as HI and I 2 , can further diffuse and penetrate PCBM film to react with Ag or Al metal electrode forming an Ag-I or Al-I insulating layer under the metal electrode, thus leading to further degradation of the pero-SCs. [11,13] In order to address this issue, an encapsulating strategy was employed. For example, thick PCBM film and bilayer structure, such as PCBM/metal oxide, [14] PCBM/PS, [15] and PEAI/PCBM, [16] can effectively reduce the discontinuity or enhance the hydrophobicity of PCBM films for preventing moisture permeation. However, the device performance was limited, due to the mismatched energy level/electron mobility between bilayers, and the increased charge recombination in thick PCBM film or bilayers. Therefore, extensive work toward designing new fullerene derivatives with good film-forming ability, [17] high electron mobility, [18] and water-resistant ability [19] have been conducted to replace PCBM as ETL, but have rarely shown both high efficiencies and high stabilities in the p-i-n pero-SCs.On the other hand, recent studies have clearly revealed that various types of defects, including vacancies, interstitials, and antisites, existing at the surface and grain boundaries of The poor long-term stability of organic-inorganic hybrid halide perovskite solar cells (pero-SCs) remains a big challenge for their commercialization.Although strategies such as encapsulation, doping, and passivation have been reported, there remains a lack of understanding of the water resistance and thermal stability of pero-SCs. A fullerene derivative, [6,6]-phenyl-C 61 -butyric acid-N,N-dimethyl-3-(2-thienyl)propanam ester (PCBB-S-N) containing a functional sulfur atom and C 60, is synthesized and employed as electron transporting layer (ETL)/i...
Mixed tin (Sn)-lead (Pb) perovskite is considered the most promising low-bandgap photovoltaic material for both pursuing the theoretical limiting efficiency of single-junction solar cells and breaking the Shockley-Queisser limitation by constructing tandem solar cells. However, their power conversion efficiencies (PCEs) are still lagging behind those of medium-bandgap perovskite solar cells (pero-SCs) due to their serious energy loss (E loss ). In this work, we used an ultra-thin bulkheterojunction (BHJ) organic semiconductor (PBDB-T:ITIC) layer as an intermediary between the hole transporting layer and Sn-Pb-based low-bandgap perovskite film to minimize E loss . It was found that this BHJ PBDB-T:ITIC intermediary simultaneously provided a cascading energy alignment in the device, facilitated high-quality Sn-Pb perovskite film growth, and passivated the antisite defects of the perovskite surface. In this simple way, the E loss of pero-SCs based on (FASnI 3 ) 0.6 (MAPbI 3 ) 0.4 (bandgap ≈ 1.25 eV) was dramatically reduced below 0.4 eV, leading to a high open-circuit voltage (V oc ) of 0.86 V. As a result, the best pero-SC showed a significantly improved PCE of 18.03% with negligible J-V hysteresis and high stability. To the best of our knowledge, the PCE of 18.03% and V oc of 0.86 V are the highest values among the low-bandgap pero-SCs to date.
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