Slow Dynamic Processes in Lead Halide Perovskite Solar Cells. Characteristic Times and Hysteresis

Abstract

Characteristic times of perovskite solar cells (PSCs) have been measured by different techniques: transient photovoltage decay, transient photoluminescence, and impedance spectroscopy. A slow dynamic process is detected that shows characteristic times in the seconds to milliseconds scale, with good quantitative agreement between transient photovoltage decay and impedance spectroscopy. Here, we show that this characteristic time is related with a novel slow dynamic process caused by the peculiar structural properties of lead halide perovskites and depending on perovskite crystal size and organic cation nature. This new process may lie at the basis of the current−voltage hysteresis reported for PSCs and could have important implications in PSC performance because it may give rise to distinct dynamical behavior with respect to other classes of photovoltaic devices. Furthermore, we show that low-frequency characteristic time, commonly associated with electronic carrier lifetime in other photovoltaic devices, cannot be attributed to a recombination process in the case of PSCs. SECTION: Energy Conversion and Storage; Energy and Charge Transport

Solution‐Grown Monocrystalline Hybrid Perovskite Films for Hole‐Transporter‐Free Solar Cells

“…[32,[34][35][36] Here, the PCE obtained from the reversely scanned J-V curve is close to that extracted from the transient current measurement, which agrees well with the trapping-detrapping model. [32] Although MAPbBr 3 crystals have an ultra-low bulk trap density, [7] defects and trap states could accumulate at the crystal surface, which is also supported by the PL study ( Figure S5, Supporting Information).…”

Optoelectronic Studies of Methylammonium Lead Iodide Perovskite Solar Cells with Mesoporous TiO2: Separation of Electronic and Chemical Charge Storage, Understanding Two Recombination Lifetimes, and the Evolution of Band Offsets during J–V Hysteresis

“…recently reported 1 sun TPV lifetimes that varied from 100 µs to 2 µs, depending on the material (MAPI or formamadinium lead iodide) and the fabrication procedure (single or two step). 5 They came to the conclusion that these decay times could not be associated with electron/hole recombination. Most other papers using transients or impedance have found a 90-200 µs characteristic time, which they have assigned to charge recombination.…”

“…There is also debate about how to correctly measure the recombination and transport times, the charge density, and even the correct measurement of efficiency. [5][6][7][8][9][10][11][12][13][14][15][16][17] The debate about characterization centers on the interpretation of various time constants that can be measured by optical and electrical means. These time constants range from <1 µs to >100 µs.…”

“…18 All three of these possibilities remain in the debate. 5,19,20,20,25 Along with the addition of crystal size effects 21 . It has been proposed that an optimum mesoporous TiO 2 film thickness minimizes the JV hysteresis.…”

Charge‐Carrier Dynamics and Mobilities in Formamidinium Lead Mixed‐Halide Perovskites

“…[ 28 ] Replacing MA in MAPbI 3 by the larger cation formamidinium HC(NH 2 ) 2 + (FA) was found to decrease the bandgap from 1.57 to 1.48 eV, [29][30][31] yield long photoluminescence (PL) lifetimes, high PCEs, [ 28 ] and lower recombination and device hysteresis. [ 32 ] Highest PCEs of 20.1% have been reported [12][13][14] to date for solar cells based on FAPbI 3 making this an attractive system to explore. In addition, the gradual replacement of the MA cation by FA through the fi lm was shown to create a mixed cation-lead-iodide PSC allowing for energetic gradients.…”