Electronic and Photovoltaic Properties of Superlattices Constructed by Organic–Inorganic Perovskites: a Theoretical Perspective

Abstract

Perovskite solar cells (PSCs) with ever-increasing power conversion efficiency (PCE) have received enormous attention over the past decade, but long-term stability is still a great challenge in practical applications. Constructing a superlattice by different perovskites is an effective approach for improving the stability and photovoltaic performance of PSCs. Herein, we report the first-principles calculations on geometric, electronic, and optoelectronic properties of superlattice structures composed of conventional perovskites MAPbI 3 , FAPbI 3 , and MAPbI 2 Br. Our calculated formation enthalpies and binding energies show that superlattice formations are exothermic processes, meaning that superlattice perovskites exhibit thermodynamic stability. The bandgaps of superlattices can be fine-tuned by the thickness of the pristine perovskite layers. The states at valence band maximum and conduction band minimum of superlattices are separated on different atomic layers, which can reduce the electron−hole recombination and is conducive to the separation and collection of charge carriers. Small effective masses of carriers and low exciton binding energies give rise to a high density, high mobility, and long lifetime of carriers in the superlattice perovskites. The estimated theoretical PCE of the superlattice reaches as high as 21.62%. This research offers a complementary strategy for designing more stable and efficient light-absorbing materials of PSCs.

A review on theoretical studies of structural and optoelectronic properties ofFA‐based perovskite materials with a focus onFAPbI3

“…Their results indicated that these superlattice structures have tunable direct band gaps, small effective electron, hole masses, and reduced electron‐hole recombination rates 188 . The properties of superlattice structures composed of conventional perovskites MAPbI 3 , FAPbI 3 , and MAPbI 2 Br were also studied by Cheng et al 189 The estimated theoretical PCE of the superlattice reaches as high as 21.62%. Cheng's group showed that the bandgaps of superlattices are related to the number of the monomer perovskite layer and can be fine‐tuned by the thickness of the pristine perovskite layers.…”

“…The PCE of these structures reaches as high as 21.62% and the band structure and photovoltaic performance of them can be fine‐tuned by controlling the thickness of the deposited perovskite. Therefore, the Br percent can play a crucial role in these materials 189 …”

“…Therefore, the Br percent can play a crucial role in these materials. 189 Through recent studies, engineering the mixed perovskites in A, B, or X sites has been the center of attention since this method appears to be a way leading to better efficiency and more stability in perovskite solar cells and tandem applications. 77,95,157,237…”

Intrinsic defects at the interface of the FAPbI3/MAPbI3 superlattice: insight from first-principles calculations

“…20 Experimental and theoretical investigations have proved that interface engineering is an effective strategy to achieve surface passivation, thereby improving the stability and efficiency of PSCs. [21][22][23][24][25][26][27] Heterojunctions consisting of two kinds of perovskite layers can provide a new paradigm for device engineering. Holmes et al 21 synthesized seven APbX 3 /MASnX 3 (A = Cs, MA, or FA; X = Br or I) heterojunctions using a combination of sequential solution and steam processing, and they found that two promising superlattice structures, MAPbBr 3 /MASnBr 3 and CsPbBr 3 /MASnBr 3 , are stable for more than 1500 hours.…”

“…25,26 In previous work, we have studied the structures and photoelectric properties of FAPbI 3 /MAPbI 3 superlattices by DFT calculations, showing that they are thermodynamically stable and exhibit good optical absorption performance. 27 Structural defects ranging from point defects to grain boundaries play a critical role in the performance of PSCs, especially the electron-hole diffusion lengths and recombination rates. 28 Some defects that create a deep level usually form nonradiative recombination centers and reduce carrier lifetime.…”