Herein, the dependence of photovoltaic performance on the additives of FAX (X = Cl, Br, and I, FA = formamidinium) and ACl [A = methylammonium (MA), Cs, Rb, and NH4] in FAPbI3‐based perovskite solar cells (PSCs) is reported. Effect of concentration on photovoltaic parameters is first screened for each additive, from which optimal concentration is determined with respect to the pristine without additive. Power conversion efficiency (PCE) is significantly improved from 16.55% to 22.51% after adding 20 mol% FACl in the perovskite precursor solution, whereas moderate increase in PCE to 20.08% and 19.97% is observed for FABr and FAI, respectively, indicating an important role of chloride. MACl and CsCl improved PCE to 20.81% and 20.59%, respectively, which is, however, inferior to FACl. A significantly increased carrier lifetime by treating FACl is responsible for the best performance. Energy dispersive X‐ray spectroscopy shows that chloride in the additive FACl is not incorporated in grain but placed on the grain boundary, which plays an important role in passivating iodide‐deficient grain boundary. The FACl additive has benefits over other additives because it cannot change the bandgap of FAPbI3.
Additive engineering has been known to be an effective method for inducing a simultaneous effect of enlarging grain size and surface passivation. As compared to the monovalent halides frequently used...
An easy transfer procedure to obtain graphene-based gas sensing devices operating at room temperature (RT) is presented. Starting from chemical vapor deposition-grown graphene on copper foil, we obtained single layer graphene which could be transferred onto arbitrary substrates. In particular, we placed single layer graphene on top of a SiO/Si substrate with pre-patterned Pt electrodes to realize a chemiresistor gas sensor able to operate at RT. The responses to ammonia (10, 20, 30 ppm) and nitrogen dioxide (1, 2, 3 ppm) are shown at different values of relative humidity, in dark and under 254 nm UV light. In order to check the sensor selectivity, gas response has also been tested towards hydrogen, ethanol, acetone and carbon oxide. Finally, a model based on linear dispersion relation characteristic of graphene, which take into account humidity and UV light effects, has been proposed.
As
a revolutionary photovoltaic technology, the perovskite solar
cell has received enormous attention, owing to excellent electronic
and optical properties of perovskite materials. The mesoporous TiO2 (m-TiO2) framework is extensively used as an electron
transport layer (ETL) to construct high-performance perovskite solar
cells (PSCs), showing efficient electron extraction capability, owing
to the enlarged perovskite/ETL interface. However, the TiO2 ETL usually involves high-density oxygen vacancies, low electron
mobility, and relatively high photocatalytic activity toward perovskite
materials. To address such issues, herein, we demonstrate the successful
construction of SnO2 quantum dot (QD)-modified m-TiO2 as an effective ETL for PSCs. It is revealed that the SnO2 QD-modified m-TiO2 ETL affords more favorable
electron extraction and transport characteristics and suppressed charge
recombination, resulting from the interfacial passivation and the
enhanced conductivity of ETLs. Furthermore, the ultrathin SnO2 QD layer incorporated at the m-TiO2/perovskite
interface effectively lowers the photocatalytic activity of TiO2 toward perovskite materials, thereby improving the long-term
device stability. Eventually, the MAPbI3- and FAPbI3-based PSCs utilizing the SnO2 QD-modified m-TiO2 ETLs obtained appreciable power conversion efficiencies of
19.09 and 20.09%, respectively, higher than those of counterpart devices
based on the conventional m-TiO2 and SnO2 ETLs.
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