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Device physics of back-contact perovskite solar cells
摘要： Back-contact perovskite solar cells (PSCs) are a promising candidate to further increase power conversion efficiency (PCE) and have been the subject of many investigations. However their full potential has not been achieved due a lack of a complete understanding of their operation from a device physics perspective. In this study, a detailed photoelectrical model for back-contact PSCs is developed by coupling a drift-diffusion description of free charge transport model with ion migration currents and emitted-carrier generation resulting from photon recycling. By studying the influence of relevant electrical parameters, the interplay between charge generation, transport and recombination, is revealed to further clarify the design principles based on devices with a back-contact structure. Although devices featuring the back-contact structure exhibit a sensitivity to electrical parameters, a high PCE exceeding 25% is predicted if the interface passivation and perovskite film quality can be well controlled. Different conduction band and valence band offsets offer various screening opportunities for functional materials with high efficiencies are introduced. Additionally, the simulated results revealed that mobile ions degrade the device performance if the average ion concentration exceeds 1016 cm?3. Furthermore, we point out that photon recycling can effectively compensate against radiative recombination, thereby resulting in an improved open circuit voltages. The results provide a new understanding of the carrier transport dynamics, ion migration, and photon recycling effects for the back-contact structure, which can be applied to a systematic improvement in the design of high efficiency PSCs.
关键词： Power conversion efficiency,Ion migration,Back-contact perovskite solar cells,Photoelectrical model,Photon recycling
更新于2025-09-19 17:13:59
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Ultrathin Nanosheets of Oxo‐functionalized Graphene Inhibit the Ion Migration in Perovskite Solar Cells
摘要： Mixed cation/halide perovskites have led to a significant increase in the efficiency and stability of perovskite solar cells. However, mobile ionic defects inevitably exacerbate the photoinduced phase segregation and self-decomposition of the crystal structure. Herein, ultrathin 2D nanosheets of oxo-functionalized graphene/dodecylamine (oxo-G/DA) are used to solve ion migration in cesium (Cs)-formamidinium (FA)-methylammonium (MA) triple-cation-based perovskites. Based on the superconducting carbon skeleton and functional groups that provide lone pairs of electrons on it, the ultrathin 2D network structure can fit tightly on the crystals and wrap them, isolating them, and thus reducing the migration of ions within the built-in electric field of the perovskite film. As evidence of the formation of sharp crystals with different orientation within the perovskite film, moiré fringes are observed in transmission electron microscopy. Thus, a champion device with a power conversion efficiency (PCE) of 21.1% (the efficiency distribution is 18.8 ± 1.7%) and a remarkable fill factor of 81%, with reduced hysteresis and improved long-term stability, is reported. This work provides a simple method for the improvement of the structural stability of perovskite in solar cells.
关键词： Ion-migration inhibition,triple cation perovskite,oxo-functionalized graphene
更新于2025-09-12 10:27:22
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Strontium Chloride Passivated Perovskite Thin Films for Efficient Solar Cells with Power Conversion Efficiency over 21% and Superior Stability
摘要： Industrialization of perovskite solar cells (PSCs) is constrained by adverse stability in the air. Herein, we report an effective strontium chloride (SrCl2) passivation upon the HC(NH2)2-CH3NH3 (FA-MA) based perovskite thin films for the suppression of non-radiative recombination. Moreover, the recombination dynamics, crystallinity, carrier transport, morphology and the elemental stoichiometry of this film were systematically studied. By optimizing the concentration of SrCl2, the corresponding devices exhibited an increased open-circuit voltage (1.00 V vs 1.09 V), in consistent with the enhanced photoluminescence lifetime. The champion passivated device showed a ascendant power conversion efficiency (PCE) about 21.11% , with over 90% retention of the primal PCE in dry air after 1000 h aging with 20% ~ 30% humidity. A superior stability and an accelerated eletron/hole extraction ability were futher observed by time-resolved photoluminescence (TRPL) spectroscopy.
关键词： Charge-transport,High-performance,Spin coating,Crystallzation,Hysteresis,Ion migration
更新于2025-09-12 10:27:22
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Improving and Stabilizing Perovskite Solar Cells with Incorporation of Graphene in the Spiro-OMeTAD Layer: Suppressed Li Ions Migration and Improved Charge Extraction
摘要： Perovskite solar cells (PSCs) have achieved a huge success in power conversion efficiency (PCE), while they still suffer from the long-term stability problem caused by the intrinsic sensitivity of perovskites to moisture. 2,2’,7,7’-tetrakis (N, N-di-p-methoxyphenylamine) 9,9’-spirobifluorene (Spiro-OMeTAD) is widely used as the hole transport layer (HTL) in typical PSCs; meanwhile bis(trifuoromethane)sulfonimide lithium salt (Li-TFSI) proves its necessity as an additive in the Spiro-OMeTAD HTL to improve the hole mobility. However, the Li+ ions bring in high hygroscopicity and water-uptake effect that both aggravate degradation of the Spiro-OMeTAD HTL and thereby of the perovskite layers. Here, we modify the Li-TFSI-based Spiro-OMeTAD HTL by adding reduced graphene oxide (rGO). We verify that rGO provides adsorption sites for Li+ ions and subsequently suppresses Li+ migration. The water-uptake effect originated from Li+ ions is thus relieved and detestable pinholes in HTL caused by Li+ ion migration are eliminated. Consequently, the rGO-incorporated HTL remarkably improves the device stability that maintains the initial PCEs within 3% loss after 700 h under 40% humidity; whereas the pristine devices almost lose the efficiency after 620 h. In addition, the good conductivity of the rGO favors hole transport in the Spiro-OMeTAD, resulting in a promotion in PCEs from 17.7% to 19.3% by incorporating rGO in HTL. Our work takes an insight into the function of rGO in the HTL and demonstrates an effective way of improving the efficiency and stability of PSCs simultaneously.
关键词： Perovskite solar cells,lithium ions,moisture stability,reduced graphene oxide (rGO),charge extraction,ion migration
更新于2025-09-11 14:15:04
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Influence of Work Function of Carrier Transport Materials with Perovskite on Switchable Photovoltaic Phenomena
摘要： The hysteresis effect and switchable photovoltaic phenomena in organo-metal halide perovskite have been observed in perovskite solar cells with certain structures and under certain measure conditions. These phenomena were favorably applied to resistive random-access memory and human-brain-mimicking devices, especially using photons as a reading or stress probe apart from using electrical probe. However, the mechanisms causing these effects are not fully understood. In this paper, the perovskite devices with different hole transporting layers, which have the work functions ranging from 5.9 eV to 3.7 eV, were fabricated and systematically characterized by current-voltage measurements and time-resolved photo-response measurements. These measurements show that the switchable photovoltaic phenomena are highly related to the work function of the hole transporting layer. The interfacial electronic structures of perovskite and several materials were studied in details using X-ray and ultraviolet photoemission spectroscopy (XPS and UPS), suggesting that the switchable photovoltaic is extensively dependent on the strong band bending effect. Light-mediated XPS measurements reveals that the degree of band bending in the perovskite layer was manipulated by charge trapping/de-trapping and hole-carrier accumulation. Based on the electrical measurements and band diagram, we propose a model that combines ion migration and charge trapping/detrapping processes to explain the switchable photovoltaic phenomena.
关键词： work function,band bending,hole transporting layer,perovskite,ion migration,charge trapping,switchable photovoltaic
更新于2025-09-11 14:15:04
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The Effect of Crystal Grain Orientation on the Rate of Ionic Transport in Perovskite Polycrystalline Thin Films
摘要： In this work, we examine the effect of microstructure on ion migration induced photoluminescence (PL) quenching in methylammonium lead iodide perovskite films. Thin films were fabricated by two methods: spin-coating, which results in randomly oriented perovskite grains, and zone-casting, which results in aligned grains. As an external bias is applied to these films, migration of ions causes a quenching of the PL signal in the vicinity of the anode. The evolution of this PL-quenched zone is less uniform in the spin-coated devices than in the zone-cast ones, suggesting that the relative orientation of the crystal grains plays a significant role in the migration of ions within polycrystalline perovskite. We simulate this effect via a simple Ising model of ionic motion across grains in the perovskite thin film. The results of this simulation align closely with the observed experimental results, further solidifying the correlation between crystal grain orientation and the rate of ionic transport.
关键词： zone-casting,ion migration,microstructure,photoluminescence,MAPbI3 perovskite
更新于2025-09-10 09:29:36
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Excess charge-carrier induced instability of hybrid perovskites
摘要： Identifying the origin of intrinsic instability for organic–inorganic halide perovskites (OIHPs) is crucial for their application in electronic devices, including solar cells, photodetectors, radiation detectors, and light-emitting diodes, as their efficiencies or sensitivities have already been demonstrated to be competitive with commercial available devices. Here we show that free charges in OIHPs, whether generated by incident light or by current-injection from electrodes, can reduce their stability, while efficient charge extraction effectively stabilizes the perovskite materials. The excess of both holes and electrons reduce the activation energy for ion migration within OIHPs, accelerating the degradation of OIHPs, while the excess holes and electrons facilitate the migration of cations or anions, respectively. OIHP solar cells capable of efficient charge-carrier extraction show improved light stability under regular operation conditions compared to an open-circuit condition where the photo-generated charges are confined in the perovskite layers.
关键词： charge-carrier extraction,ion migration,organic–inorganic halide perovskites,stability,solar cells
更新于2025-09-09 09:28:46