No abstract

The nature of the photoconductivity in solution-processed films of methylammonium lead iodide perovskite is investigated by determining the variation of the photoconductive response with temperature. Ultrabroadband terahertz (THz) photoconductivity spectra in the 0.3-10 THz range can be reproduced well by a simple Drude-like response at room temperature, where free charge carrier motion is characterized by an average scattering time. The scattering time determined from Drude fits in the 0.3-2THz region increases from ∼4 fs at 300 K (tetragonal phase; mobility of ∼27 cm(2) V(-1) s(-1)) to almost ∼25 fs at 77 K (orthorhombic phase, mobility of ∼150 cm(2) V(-1) s(-1)). For the tetragonal phase (temperature range 150< T < 300 K) the scattering time shows a ∼T(-3/2) dependence, approaching the theoretical limit for pure acoustic phonon (deformation potential) scattering. Hence, electron-phonon, rather than impurity scattering, sets the upper limit on free charge transport for this perovskite.

On-chip micro-supercapacitors (MSCs) are important Si-compatible power-source backups for miniaturized electronics. Despite their tremendous advantages, current on-chip MSCs require harsh processing conditions and typically perform like resistors when filtering ripples from alternating current (AC). Herein, we demonstrated a facile layer-by-layer method towards on-chip MSCs based on an azulene-bridged coordination polymer framework (PiCBA). Owing to the good carrier mobility (5×10 cm V s ) of PiCBA, the permanent dipole moment of azulene skeleton, and ultralow band gap of PiCBA, the fabricated MSCs delivered high specific capacitances of up to 34.1 F cm at 50 mV s and a high volumetric power density of 1323 W cm . Most importantly, such MCSs exhibited AC line-filtering performance (-73° at 120 Hz) with a short resistance-capacitance constant of circa 0.83 ms.

Methylammonium lead iodide perovskite is an outstanding semiconductor for photovoltaics. One of its intriguing peculiarities is that the band gap of this perovskite increases with increasing lattice temperature. Despite the presence of various thermally accessible phonon modes in this soft material, the understanding of how precisely these phonons affect macroscopic material properties and lead to the peculiar temperature dependence of the band gap has remained elusive. Here, we report a strong coupling of a single phonon mode at the frequency of ~ 1 THz to the optical band gap by monitoring the transient band edge absorption after ultrafast resonant THz phonon excitation. Excitation of the 1 THz phonon causes a blue shift of the band gap over the temperature range of 185 ~ 300 K. Our results uncover the mode-specific coupling between one phonon and the optical properties, which contributes to the temperature dependence of the gap in the tetragonal phase.

On-chip micro-supercapacitors (MSCs) are important Si-compatible power-source backups for miniaturized electronics.D espite their tremendous advantages,c urrent onchip MSCs require harsh processing conditions and typically perform like resistors when filtering ripples from alternating current (AC). Herein, we demonstrated af acile layer-by-layer method towardso n-chip MSCs based on an azulene-bridged coordination polymer framework (PiCBA). Owing to the good carrier mobility (5 10 À3 cm 2 V À1 s À1 )ofPiCBA, the permanent dipole moment of azulene skeleton, and ultralow band gap of PiCBA, the fabricated MSCs delivered high specific capacitances of up to 34.1 Fcm À3 at 50 mV s À1 and ahigh volumetric power density of 1323 Wcm À3 .M ost importantly,s uch MCSs exhibited AC line-filtering performance (À738 8 at 120 Hz) with ashort resistance-capacitance constant of circa 0.83 ms.On-chip electrochemical energy storage devices, [1] such as micro-supercapacitors (MSCs) and microbatteries,h ave attracted tremendous attention in the past few years because of the rapid development of mobile electronics,w ireless sensors,a nd medical implants.C ompared with micro-batteries,on-chip MSCs have many advantages owing to their rapid energy-harvesting features,b urst-mode power delivery,a nd, in particular,c ompatibility with the Si industry. [1b, 2] Recent studies have focused on the thin-film fabrication of MSCs by using nanostructured functional materials such as graphene, [1d,3] graphene-based nanocomposites, [4] monolithic carbide-derived carbon, [1a] mesoporous conducting polymers, [5] and several other pseudocapacitive materials. [6] However, most devices based on these materials require harsh processing operation steps such as the high-temperature fabrication of electrode films,m etal electrode deposition, electrode gap generation by oxygen plasma, and the wet chemistry etching method. Such procedures lead to the easy cracking and delamination of active films from substrates,s uch as with Si wafers and Kapton films. [1b] Therefore,the development of Sicompatible MSCs with easy and cheap fabrication procedures is essential to enable their practical applications.Alternating current (AC) line-filtering,w hich can filter the AC ripple on the line-powered devices,isone of the most important tasks in the field of renewable electronic power systems such as power generation by using wind and tidal power. [7] However,t raditional aluminum electrolytic capacitors (AECs), which are widely used for this purpose,h ave al ow energy density and large volume size.T herefore, supercapacitors,p articularly MSCs,t hat possess an AC linefiltering ability,h igh energy density,a nd minimal size,a re ideal alternatives to AECs.T raditionally,p orous carbonbased supercapacitors exhibit poor AC line-filtering performance (resistance-capacitance [RC] time constant % 1s) compared with AECs (RC time constants = 8.3 ms) [7c] because of the slow and internal response of the polarization [7c] and limited signal propagation [7a] from the electrodes...