Expanded Phase Distribution in Low Average Layer-Number 2D Perovskite Films: Toward Efficient Semitransparent Solar Cells

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Optoelectronic and Energy Level Exploration of Bismuth and Antimony-Based Materials for Lead-Free Solar Cells

Inés Garcia Benito, Hiroyuki Kanda, Mohammad Khaja Nazeeruddin, Ryosuke Nishikubo

Bismuth- and antimony-based materials, such as A(3)M(2)X(9) and AMSX(2) (A = cation, M = Bi, Sb, S = sulfur, X = halogen), are promising candidates as the counterpart to lead halide perovskite. However, the large number of different compositions and crystal structures (dimer, perovskite, etc.) has made these materials largely overlooked; thus, an intuitive evaluation strategy is required. Here, we present a comprehensive study of the energy levels (bandgap, valence band maximum, etc.) and optoelectronics (photoconductivity and charge transfer to charge transport material) of the Bi - and Sb-based materials, which include 6 crystal categories with 44 compositions, by using time-resolved microwave conductivity (TRMC). Importantly, we found an efficient hole transfer from the Sb-based materials to the hole transport materials with the inclusion of the thiophene component, leading to an improved power conversion efficiency of 2.91% for Sb2S3-containing SbSI, prepared by a novel one-step method. Our study establishes a key rule for exploring active layer compositions and designing device structures, which would accelerate the evolution of Bi- and Sb-based lead-free solar cells.

2020

Defect Suppression in Oriented 2D Perovskite Solar Cells with Efficiency over 18% via Rerouting Crystallization Pathway

Yong Ding, Cheng Liu, Xuehui Liu, Mohammad Khaja Nazeeruddin, Olga Syzgantseva, Yi Yang

Vertically oriented 2D perovskites exhibit promising optoelectronic properties and intrinsic stability, but their photovoltaic application is still limited by the low power conversion efficiency (PCE) compared to 3D analogs. Here, a new crystallization pathway (RCP) is reported to suppress defects in vertically oriented 2D perovskite caused by its over-rapid self-assembly behavior. By controlling the specific adsorption of an ammonium halide additive on different perovskite crystal planes, the dynamic preferred growth of (111) plane is intentionally restrained, and the minority (202) planes emerge as secondary nucleation sites to stimulate the creation of large grains. As the halogen-regulated deprotonation of ammonium proceeds, the (111) crystal plane gradually recovers its growth dominance, and a vertically oriented 2D perovskite film finally forms with high homogeneity, reduced trap density of states, and desired carrier transport/collection kinetics. Solar cells using RCP-2D films show a highly reproducible and stable PCE reaching 18.5% with a high fill factor of 83.4%. These findings provide critical missing information on simultaneously achieving highly oriented and less defective 2D perovskite films for excellent device performance.

2021

Formate as Anti-Oxidation Additives for Pb-Free FASnI(3) Perovskite Solar Cells

Jaeki Jeong, Jinhyun Kim, Jiyoun Seo

Pb-free Sn-based perovskite solar cells (PSCs) have significant potential for application in photovoltaic devices because oftheir suitable bandgap, low exciton binding energy, high carrier mobility, and long diffusion length. However, their performance is hampered by several issues. Sn-based perovskites are highly susceptible to oxidation, which induces a high concentration of defects and degrades the chemical stability of the perovskite crystals. Herein, the anion formate (HCOO-) can effectively suppress the oxidation of Sn in the pure formamidinium tin triiodide (FASnI(3)) perovskite without using A-site cationic additives. Moreover, the presence of formate results in a uniform pinhole-free perovskite film with a low trap density, reduced charge carrier recombination, and improved charge extraction. Density functional theory calculations show that formate-treated FASnI(3) has improved stability against oxidative Sn degradation. The formate-treated PSC achieves a power conversion efficiency of 12.11% at a high open-circuit voltage of 0.71 V. The device exhibits improved stability in ambient air in which it maintained over 80% of its initial power conversion efficiency after 180 min because oxidation is inhibited owing to the strong interaction between Sn and formate.

WILEY-V C H VERLAG GMBH2022