ABSTRACT
The inorganic lead-free Cs2AgBiBr6 double perovskite structure is the promising development direction in perovskite solar cells (PSCs) to solve the problem of the instability of the APbX3 structure and lead toxicity. However, the low short-circuit current and power conversion efficiency (PCE) caused by the low crystallization of Cs2AgBiBr6 greatly limit the optoelectronic application. Herein, we adopt a simple strategy to dope single-layered MXene nanosheets into titania (Ti3C2Tx@TiO2) as a multifunctional electron transport layer for stable and efficient Cs2AgBiBr6 double PSCs. The single-layered MXene nanosheets significantly improve the electrical conductivity and electron extraction rate of TiO2; meanwhile, the single-layered MXene nanosheets change the surface wettability of the electron transport layer and promote the crystallization of the Cs2AgBiBr6 double perovskite in solar cell devices. Therefore, the PCE went up by more than 40% to 2.81% compared to that of a TiO2 based device, and the hysteresis was greatly suppressed. Furthermore, the device based on Ti3C2Tx@TiO2 showed the long-term operating stability. After storing the device for 15 days under ambient air conditions, the PCE still remained a retention rate of 93% of the initial one. Our finding demonstrates the potential of Ti3C2Tx@TiO2 in electron transfer material of high-performance double PSCs.
ABSTRACT
Organic-inorganic halide perovskite solar cells (PSCs) still suffer from stability issues which are caused by possible erosions from moisture, ultraviolet (UV) light, heat, and so forth. An electron-transporting layer (ETL), that is, TiO2, is a key component for state-of-the-art PSCs. However, UV-caused desorption of O2- in TiO2 would accelerate the degradation of PSCs. Herein, we explored perovskite oxide, NaTaO3, for the first time as an alternative ETL in PSCs. NaTaO3 as an ETL can effectively avoid the damage from UV irradiation, inhibit the degradation of the perovskite layer, and improve the overall stability of the PSC. PSCs fabricated with NaTaO3 yielded a power conversion efficiency (PCE) of 21.07% with a retention of more than 80% of this initial PCE after 240 min UV irradiation in air while the reference device with a PCE of 20.16% can only retain about 53% of its initial PCE after the same testing condition. The developed stable perovskite oxide material of NaTaO3 provides the diversification of electron-selective contact for highly efficient and stable PSCs.
ABSTRACT
Perovskite solar cells have attracted worldwide attention as one of the key research areas in the field of thin-film photovoltaics. Although they exhibit easy solution processability, it is important to effectively control the crystallization of the light-absorbing layer, which affects the performance and stability of devices. Here, we present lead oxalate (PbC2O4) as a nonhalide lead constituent of the perovskite precursor solution, which contributes to anion replacement during thin film annealing. This strategy limits the perovskite nucleation rate and retards crystallization. As a result, we achieved excellent perovskite films with larger grains and fewer defects. The open-circuit voltage of the optimal device under 1 sun illumination rose to 1.12 V with a power conversion efficiency (PCE) of 20.20%. In addition, the indoor PCE at 1000 lux can reach 34.86%. This nonhalide lead compound dopant provides a guide for the crystallization of perovskite materials and paves a way for the fabrication of nonhalide perovskite solar cells.
ABSTRACT
Addressing the toxicity issue in lead-based perovskite compounds by seeking other nontoxic candidate elements represents a promising direction to fabricate lead-free perovskite solar cells. Recently, Cs2AgBiBr6 double perovskite achieved by replacing two Pb2+ with Ag+ and Bi3+ in the crystal lattice has drawn much attention owing to the convenient substitution of its chemical compositions. Herein, the dependence of the optoelectronic properties and corresponding photovoltaic performance of Cs2AgBiBr6 thin films on the deposition methods of vacuum sublimation and solution processing is investigated. Compared to the vacuum sublimation based one, the solution-processed Cs2AgBiBr6 shows inherently higher crystallinity, narrower electronic bandgap, longer photoexcitation lifetime, and higher mobility. The excellent optoelectronic properties are attributed to the accurate composition stoichiometry of Cs2AgBiBr6 films based on solution processing. These merits enable the corresponding perovskite solar cells to deliver a champion power conversion efficiency (PCE) of 2.51%, which is the highest PCE in the Cs2AgBiBr6-based double perovskite solar cells to date. The finding in this work provides a clear clue that a precise composition stoichiometry could guarantee the formation of high quality multicomponent perovskite films.
ABSTRACT
A new approach to improve the quality of MAPbI3 - x Cl x perovskite film was demonstrated. It involves annealing the precursor film after pumping away the solvent, which can decrease the influence of solvent evaporation rate for the growth of the MAPbI3 - x Cl x perovskite film. The resulting film showed improved morphology, stronger absorption, fewer crystal defects, and smaller charge transfer resistance. The corresponding device demonstrated enhanced performance when compared with a reference device. The averaged value of power conversion efficiency increased from 10.61 to 12.56 %, and a champion efficiency of 14.0 % was achieved. This work paves a new way to improve the efficiency of perovskite solar cells.
ABSTRACT
The electrical doping nature of a strong electron acceptor, 1,4,5,8,9,11-hexaazatriphenylene hexacarbonitrile (HATCN), is investigated by doping it in a typical hole-transport material, N,N'-bis(naphthalen-1-yl)-N,N'-diphenylbenzidine (NPB). A better device performance of organic light-emitting diodes (OLEDs) was achieved by doping NPB with HATCN. The improved performance could, in principle, arise from a p-type doping effect in the codeposited thin films. However, physical characteristics evaluations including UV-vis absorption, Fourier transform infrared absorption, and X-ray photoelectron spectroscopy demonstrated that there was no obvious evidence of charge transfer in the NPB:HATCN composite. The performance improvement in NPB:HATCN-based OLEDs is mainly attributed to an interfacial modification effect owing to the diffusion of HATCN small molecules. The interfacial diffusion effect of the HATCN molecules was verified by the in situ ultraviolet photoelectron spectroscopy evaluations.
