Efficient Flexible Perovskite Solar Cells with Reduced Hysteresis Employing Cobalt Nitrate Treated SnO₂

Abstract

Flexible perovskite solar cells (PSCs) have great potential for portable electronics, however, suffer from large hysteresis in regular structure. Insufficient charge extraction in commonly used tin dioxide (SnO 2 ) electron transporting layer (ETL) is regarded as one possible origin of hysteresis due to the low crystallinity and energy level mismatching. Here, the hysteresis of flexible PSCs is suppressed by synthesizing cobalt-modified SnO 2 ETLs, which improve electron extraction capability due to the high carrier mobility and well-aligned energy levels. Moreover, cobalt modification passivates the defects on the ETL surface, facilitates sequential perovskite film growth, and inhibits carrier recombination. As a result, flexible PSCs with efficiencies exceeding 20% are obtained with significantly reduced hysteresis and enhanced illumination stability. Comprehensive optoelectronic simulations are conducted to unveil the deep mechanisms of eliminated hysteresis. The proposed work provides an efficient and facile strategy for the fabrication of high-performance flexible PSCs upon future commercialization.

Annealing-Free SnO2 Layers for Improved Fill Factor of Perovskite Solar Cells

“…(The statistical histogram of FF of PSCs based on A-SnO 2 and NPE-SnO 2 ETLs is shown in Figure S7b). Further, there is almost no hysteresis for PSCs with the help of NPE, which can be attributed to its significantly suppressed interfacial charge accumulation and recombination . As shown in Figure b, the external quantum efficiency (EQE) results confirm the integrated J SC of PSCs based on A-SnO 2 and NPE-SnO 2 ETLs is to be 24.10 and 23.96 mA/cm 2 , respectively.…”

“…35 Further, there is almost no hysteresis for PSCs with the help of NPE, which can be attributed to its significantly suppressed interfacial charge accumulation and recombination. 36 As shown in Figure 5b, the external quantum efficiency (EQE) results confirm the integrated J SC of PSCs based on A-SnO 2 and NPE-SnO 2 ETLs is to be 24.10 and 23.96 mA/cm 2 , respectively. The corresponding PCE statistical distribution of the PSCs on both ETLs in Figure 5c intuitively reflects the positive effect of NPE-SnO 2 on device performance.…”

Low Temperature Processed SnO2 Electron Transporting Layer from Tin Oxalate for Perovskite Solar Cells

“…The slopes of the I – V curves monotonically decrease with increasing H 2 O 2 volumes, indicating that conductivity of the SnO 2 ETLs are decreased with higher H 2 O 2 volumes. According to refs and , the O–H species can act as traps on the surface of SnO 2 film, which have a detrimental effect on the charge transportation of the SnO 2 ETLs. Therefore, the 250 μL SnO 2 ETL with the lowest content of O–H species exhibits the highest electrical conductivity.…”

Transient Response Mismatch: A Limiting Factor of Perovskite Photodetectors

“…Universally, hybrid perovskite materials show mixed ionicelectronic behaviors due to the fragile lattice and low defectformation energy. [28][29][30] Besides the electrons and holes, the Electron affinity χ eV 2.5 [31] 3.93 [31] 4.0 [39] Band gap E g eV 2.93 [31] 1.55 [31] 3.6 [39] Relative permittivity ε r 3 [32] 6.5 [35] 9 [40] Effective DOS for electrons N c cm −3 10 19 [33] 0.23 m 0 [36] 0.3 m 0 [41] Effective DOS for holes N v cm −3 10 19 [33] 0.29 m 0 [36] 1 m 0 [41] Electron mobility µ n cm 2 V −1 s −1 1 × 10 −7 -1 × 10 −4 [44] 2 [37] 0.004 [39] Hole mobility µ p cm 2 V −1 s −1 1 × 10 −4 -0.8 [44] 2 [37] 0.004 [39] SRH life time τ n =τ p µs 0.1 [34] 0.06 [38] 1300 [42] Radiative recombination coefficient B rad cm −3 s −1 -3.27 × 10 −11 [38] -Auger recombination coefficient C n =C p cm 6 s −1 -0.88 × 10 −29 [38] movable ions need also to be considered. These off-site ionic charges can be driven by the electric field to form a potential barrier and affect carrier transport.…”