Graphene-Induced Improvements of Perovskite Solar Cell Stability: Effects on Hot-Carriers

Abstract

Hot-carriers, that is, charge carriers with an effective temperature higher than that of the lattice, may contribute to the high power conversion efficiency (PCE) shown by perovskite-based solar cells (PSCs), which are now competitive with silicon solar cells. Hot-carriers lose their excess energy in very short times, typically in a few picoseconds after excitation. For this reason, the carrier dynamics occurring on this time scale are extremely important in determining the participation of hot-carriers in the photovoltaic process. However, the stability of PSCs over time still remains an issue that calls for a solution. In this work, we demonstrate that the insertion of graphene flakes into the mesoscopic TiO 2 scaffold leads to stable values of carrier temperature. In PSCs aged over 1 week, we indeed observe that in the graphene-free perovskite cells the carrier temperature decreases by about 500 K from 1800 to 1300 K, while the graphene-containing cell shows a reduction of less than 200 K after the same aging time delay. The stability of the carrier temperature reflects the stability of the perovskite nanocrystals embedded in the mesoporous graphene-TiO 2 layer. Our results, based on femtosecond transient absorption measurements, show that the insertion of graphene can be beneficial for the design of stable PSCs with the aim of exploiting the hot-carrier contribution to the PCE of the PSCs.

Hot carrier relaxation in Cs2TiIyBr6−y (y = 0, 2 and 6) by a time-domain ab initio study

“…40 It has demonstrated that extracting the hot carriers before they totally relax will be the core method for new generation high-efficiency solar cells. 41,42 The hot carrier relaxation is an intraband charge dynamic process, which is inevitably affected by the density of states (DOS) of the valence band (VB) and the conduction band (CB). 21,25,43 Fig.…”

Review of fabrication methods of large-area transparent graphene electrodes for industry

“…PCEs are notorious for degrading (via e.g., light-induced degradation [185,186], humidity [187,188], and perovskite-metal reactions due to interdiffusion [189,190]), and even the best PSCs have lifetimes of only thousands of hours [191]. Graphene has been used as a stabilizing agent as, e.g., a protective layer [192][193][194], and transport layer [195][196][197][198][199] and electrode material [200][201][202][203].…”

A two-fold engineering approach based on Bi2Te3 flakes towards efficient and stable inverted perovskite solar cells

“…[1][2][3][4] Meanwhile, the exceptional optoelectronic properties of 2D materials and their compatibility with large-scale, solutionprocessable methods (e.g., roll-to-roll printing techniques) lay the ground for the direct integration of low-cost and flexible photovoltaic devices in emerging smart and multifunctional technologies. [5][6][7][8][9][10][11] The beneficial impact of graphene and related 2D materials in PSCs has been demonstrated both in mesoporous [12][13][14][15][16] and inverted planar structures, [17][18][19] as well as in their corresponding tandem systems. 20 Beyond graphene and its derivatives, various 2D material families have been tested including transition metal dichalcogenides, 21 MXenes, 13,22 phosphorene 23,24 and antimonene, 25 just to name a few.…”