Lead Halide Residue as a Source of Light-Induced Reversible Defects in Hybrid Perovskite Layers and Solar Cells

Abstract

Advanced characterization methods avoiding transient effects in combination with solar cell performance monitoring reveal details of reversible light-induced perovskite degradation under vacuum. A clear signature of related deep defects in at least the 1 ppm range is observed by low absorptance photocurrent spectroscopy. An efficiency drop, together with deep defects, appears after minutes-long blue illumination and disappears after 1 h or more in the dark. Systematic comparison of perovskite materials prepared by different methods indicates that this behavior is caused by the lead halide residual phase inherently present in material prepared by the two-step method. X-ray photoelectron spectroscopy confirms that lead halide when illuminated decomposes into metallic lead and mobile iodine, which diffuses into the perovskite phase, likely producing interstitial defects. Single-step preparation, as well as preventing lead halide illumination, eliminates this effect.

Ligand‐Modulated Excess PbI2 Nanosheets for Highly Efficient and Stable Perovskite Solar Cells

“…[ 24 ] It also results in the inhibited charge transport and accelerated degradation of perovskite layer likely due to the photodecomposition of PbI 2 and the increasing ionic movement. [ 24,26–28 ] Therefore, it is crucial to modulate the excess PbI 2 in perovskite films to achieve high efficiency and stable PSCs.…”

CuCrO2 Nanoparticles Incorporated into PTAA as a Hole Transport Layer for 85 °C and Light Stabilities in Perovskite Solar Cells

“…[ 1 , 2 , 3 , 4 , 5 , 6 , 7 , 8 , 9 , 10 , 11 ]. However, its relatively poor stability is still a main bottleneck toward commercialization, which becomes more serious at elevated temperatures or under constant illumination due to the rapid degradation of materials along with the accelerated formation and migration of defects [ 12 , 13 , 14 , 15 , 16 , 17 , 18 ]. One of the most vulnerable components is traditional organic small-molecule-based hole transport layers (HTL) such as 2,2′,7,7′-tetrakis(N,N-di-p-methoxyphenylamine)-9,9′-spirobifuorene (spiro-OMeTAD), which can easily decompose under the presence of heat [ 19 , 20 ].…”

Towards Quantitative Interpretation of Fourier-Transform Photocurrent Spectroscopy on Thin-Film Solar Cells

“…Sub-bandgap absorptance spectroscopy is a relatively simple defect quantification method, which is well established in the material science of thin-film photovoltaic (PV) materials, such as microcrystalline silicon [1], hydrogenated amorphous silicon (a-Si:H) [2], organic semiconductors [3] and also recently hybrid perovskite materials [4][5][6][7]. Whereas other methods, such as conductivity or photoluminescence, are difficult to interpret and may give results affected by transient effects, sub-bandgap absorptance photoluminescence, are difficult to interpret and may give results affected by transient effects, subbandgap absorptance spectroscopy can already provide a relatively universal indication of semiconductor quality by looking at the sub-bandgap absorptance and the steepness of the absorption edge.…”

“…The advantage of FTPS compared to PDS is the ability to measure the defect density of absorber layers in complete solar cells. In hybrid perovskites, the main difference might be the lead iodide phase that exhibits differently [4,6,7], while in the case of a-Si:H the main difference is the sensitivity to the surface defects, that is higher in PDS, but can also distort FTPS spectra (see Figure 1a). Surface defect absorption may lead to erroneous features on the apparent (as evaluated) absorption coefficient.…”