Cs_xFA_1–xPb(I_1–yBr_y)₃ Perovskite Compositions: the Appearance of Wrinkled Morphology and its Impact on Solar Cell Performance

Abstract

We report on the formation of wrinkle-patterned surface morphologies in cesium formamidinium based Cs x FA 1-x Pb(I 1-y Br y) 3 perovskite compositions with x = 0-0.3 and y = 0-0.3 under various spin-coating conditions. By varying the Cs and Br content, perovskite precursor solution concentration, and spin-coating procedure, the occurrence and characteristics of the wrinkleshaped morphology can be tailored systematically. Cs 0.17 FA 0.83 Pb(I 0.83 Br 0.17) 3 perovskite layers were analyzed regarding their surface roughness, microscopic structure, local and overall composition, and optoelectronic properties. Application of these films in p-in perovskite solar cells (PSCs) with ITO/NiO x /perovskite/C 60 /BCP/Cu architecture resulted in up to 15.3% and 17.0% power conversion efficiency for the flat and wrinkled morphology, respectively. Interestingly, we find slightly red-shifted photoluminescence (PL) peaks for wrinkled areas and we are able to directly correlate surface topography with PL peak mapping. This is attributed to differences in local grain size, while there is no indication for compositional de-mixing in the films. We show that perovskite composition, crystallization kinetics, and layer thickness strongly influence the formation of wrinkles which is proposed to be related to the release of compressive strain during perovskite crystallization. Our work helps to better understand film formation and to further improve efficiency of PSCs with widely used mixed perovskite compositions.

2D/3D Heterostructure for Semitransparent Perovskite Solar Cells with Engineered Bandgap Enables Efficiencies Exceeding 25% in Four‐Terminal Tandems with Silicon and CIGS

“…The devices were not subjected to any pre‐conditioning. In order to average over possible slight variations in the EQE spectra of the bottom c‐Si and CIGS cells when measured below the perovskite filters, which can be induced by inhomogeneous scattering and transmission properties due to typical thickness variations of double‐cation FA 0.83 Cs 0.17 Pb(I 1− y Br y ) 3 perovskite films (“wrinkle structure,” compare Braunger et al and Bush et al), [ 111,112 ] a large illumination spot was used. The absolute EQE values and hence integrated J SC of the CIGS bottom cells were corrected to account for the finger lines of the metal grid (shading effect).…”

A Review of Diverse Halide Perovskite Morphologies for Efficient Optoelectronic Applications

“…Braunger et al also reported the formation of wrinkled perovskite morphology based on Cs x FA 1− x Pb(I 1− y Br y ) 3 composition by optimizing the contents of Cs and Br, precursor solution concentration and spin‐coating parameters. It is proposed that the formation of wrinkled morphologies is stemmed from the release of compressive strain within the perovskite film …”

“…Braunger et al reported the PSCs based on wrinkled perovskite morphology, which exhibited improved PCE up to 17% as compared to that of flat perovskite morphology‐based device (PCE = 14.7%). The improved PCE can be attributed to the enhanced light harvesting and suppressed nonradiative combination originated from the wrinkled perovskite morphology . We for the first time fabricated the novel bilayered MAPbI 3 perovskite film featuring a maze‐like top layer and a dense bottom layer with the assist of MACl additive.…”

Enhanced optical path and electron diffusion length enable high-efficiency perovskite tandems

“…In general, the external quantum efficiency (EQE) of efficient single-junction perovskite cells with opaque rear-mirror contacts (metal) is above 80% near the bandedge [17][18][19] , while that of semi-transparent cells show a lower value (around 70%) in the same spectral range 4,13,[20][21][22] . Employing high-quality and thick active layers to overcome insufficient photon absorption has advanced Sn-based perovskite solar cells 4,5,23 ; however, for Pb-based perovskites, thick films exhibit inhomogeneous morphologies 24,25 and limited carrier diffusion lengths [26][27][28] .…”