Concentration-Dependent Impact of Alkali Li Metal Doped Mesoporous TiO₂ Electron Transport Layer on the Performance of CH₃NH₃PbI₃ Perovskite Solar Cells

Abstract

TiO 2 is most commonly employed as an electron transport layer (ETL) in mesoscopic n−i−p perovskite solar cells (PSCs). However, the low electron mobility, low electrical conductivity, and high electronic trap states of TiO 2 may have negative impacts on further enhancement of PSC performance. Metal doping is an efficient way to improve the electronic properties of TiO 2 films. In this work, we investigate the concentration-dependent impact of alkali lithium metal doping of the mesoporous TiO 2 ETL on the performance of mesoscopic CH 3 NH 3 PbI 3 PSCs. It was found that Li doping results in remarkable improvement in electrical conductivity and electron mobility and reduces the number of electronic trap states arising due to the oxygen vacancies within TiO 2 lattice. Such enhancements led to an enhanced charge extraction and transport and reduced charge recombination rate at the perovskite/ mesoporous TiO 2 interface as revealed by steady-state photoluminescence (PL) and time-resolved PL (TRPL) spectra, and resulted in an increase in the V OC , J SC , and FF of the PSCs. Moreover, the J−V curve hysteresis behavior after Li doping was effectively suppressed due to the reduced charge accumulation and recombination at the TiO 2 /perovskite interface. Consequently, the device performance relies on the concentration of alkali lithium metal doping, and the power conversion efficiency (PCE) of the PSC was significantly improved from 13.64% to 17.59% with reduced the J−V curve hysteresis behavior for a Li doped mesoporous TiO 2 layer with an optimized concentration of 30 mg/mL.

The Optoelectrical Properties of Li: TiO2/p‐Si Photodiodes for Various Li Doping

“…They reported that the carrier concentrations of undoped TiO 2 film increased from 4.93 × 10 9 to 6.43 × 10 10 cm −3 , and the resistivity of the undoped film decreased from 3.69 × 10 6 to 4.06 × 10 5 Ω cm after 5.0 mol% Li doping. Amalathas et al [ 13 ] investigated the influence of alkali Li‐doped on the electrical features of TiO 2 , which was utilized as an electron transport layer for perovskite solar cell application. They reported that the electrical conductivity of undoped TiO 2 increased from 4.39 × 10 −7 to 1.84 × 10 −6 mS cm −1 with 30 mg mL −1 Li doping.…”

“…According to the limited Li-doped TiO 2 films studies in the literature, Li doping is an effective way of increasing the conductivity of TiO 2 films. [10,11,13] Yan et al [10] have investigated the influence of Li doping on the crystal structure, and the optical and electrical features of TiO 2 thin films. They reported that the carrier concentrations of undoped TiO 2 film increased from 4.93 Â 10 9 to 6.43 Â 10 10 cm À3 , and the resistivity of the undoped film decreased from 3.69 Â 10 6 to 4.06 Â 10 5 Ω cm after 5.0 mol% Li doping.…”

“…[11] There are many methods for increasing electrical conductivity and mobility of TiO 2 as well as adjusting energy levels and reducing electronic trap states. [10,12,13] One of these methods is the doping process with one or more elements. Lithium (Li) doping is an effective method for the passivation of surface defects and enhancement of carrier transport by decreasing the density of subbandgap states of TiO 2 .…”

Mechanism understanding for stripping electrochemistry of Li metal anode

“…It is reported that Li metal has been an effective additive to improve the electronic properties of electron transport layer (ETL) employed in perovskite solar cells. 212,213 Additionally, it is critical to promote the uniform electron transfer on the Li metal, the conductive host as well as the current collector with the aim to avoid the formation of dead Li.…”

Improving Hole‐Conductor‐Free Fully Printable Mesoscopic Perovskite Solar Cells’ Performance with Enhanced Open‐Circuit Voltage via the Octyltrimethylammonium Chloride Additive

“…[ 17 ] Peter et al doped mesoporous TiO 2 with alkali lithium metal to reduce the density of electron traps raised by oxygen vacancies in TiO 2 , and realized a reduced charge recombination at TiO 2 /perovskite interface. [ 18 ] Ma et al obtained a better contact at TiO 2 /perovskite interface by immersing TiO 2 into NaCl solution to passivate the trap states on the surface of TiO 2 , resulting in a better electronic transport properties. [ 19 ] Sidhik et al prepared Co‐doped mesoporous TiO 2 to passivate the electronic defect levels or space‐charge regions caused by oxygen vacancies in TiO 2 , and achieved faster electron transport and collection.…”