Blending of n-type Semiconducting Polymer and PC61BM for an Efficient Electron-Selective Material to Boost the Performance of the Planar Perovskite Solar Cell

Minimization of Energy Level Mismatch of PCBM and Surface Passivation for Highly Stable Sn-Based Perovskite Solar Cells by Doping n-Type Polymer

Developing high-performance and stable Sn-based perovskite solar cells (PSCs) is difficult due to the inherent tendency of Sn2+ oxidation and, the huge energy mismatch between perovskite and Phenyl-C61-butyric acid methyl ester (PCBM), a frequently employed electron transport layer (ETL). This study demonstrates that perovskite surface defects can be passivated and PCBM's electrical properties improved by doping n-type polymer N2200 into PCBM. The doping of PCBM with N2200 results in enhanced band alignment and improved electrical properties of PCBM. The presence of electron-donating atoms such as S, and O in N2200, effectively coordinates with free Sn2+ to prevent further oxidation. The doping of PCBM with N2200 offers a reduced conduction band offset (from 0.38 to 0.21 eV) at the interface between the ETL and perovskite. As a result, the N2200 doped PCBM-based PSCs show an enhanced open circuit voltage of 0.79 V with impressive power conversion efficiency (PCE) of 12.98% (certified PCE 11.95%). Significantly, the N2200 doped PCBM-based PSCs exhibited exceptional stability and retained above 90% of their initial PCE when subjected to continuous illumination at maximum power point tracking for 1000 h under one sun.

Chemical Bridge-Mediated Heterojunction Electron Transport Layers Enable Efficient and Stable Perovskite Solar Cells

Perovskite solar cells (PSCs) emerged as potential photovoltaic energy-generating devices developing in recent years because of their excellent photovoltaic properties and ease of processing. However, PSCs are still reporting efficiencies much lower than their theoretical limits owing to various losses caused by the charge transport layer and the perovskite. In this regard, herein, an interface engineering strategy using functional molecules and chemical bridges was applied to reduce the loss of the heterojunction electron transport layer. As a functional interface layer, ethylenediaminetetraacetic acid (EDTA) was introduced between PCBM and the ZnO layer, and as a result, EDTA simultaneously formed chemical bonds with PCBM and ZnO to serve as a chemical bridge connecting the two. DFT and chemical analyses revealed that EDTA can act as a chemical bridge between PCBM and ZnO, passivate defect sites, and improve charge transfer. Optoelectrical analysis proved that EDTA chemical bridge-mediated charge transfer (CBM-CT) provides more efficient interfacial charge transport by reducing trap-assisted recombination losses at ETL interfaces, thereby improving device performance. The PSC with EDTA chemical bridge-mediated heterojunction ETL exhibited a high PCE of 21.21%, almost no hysteresis, and excellent stability to both air and light.

Moisture-Resistant FAPbI3 Perovskite Solar Cell with 22.25 % Power Conversion Efficiency through Pentafluorobenzyl Phosphonic Acid Passivation

Perovskite solar cells (PSCs) have shown great promise for photovoltaic applications, owing to their low-cost assembly, exceptional performance, and low-temperature solution processing. However, the advancement of PSCs towards commercialization requires improvements in efficiency and long-term stability. The surface and grain boundaries of perovskite layer, as well as interfaces, are critical factors in determining the performance of the assembled cells. Defects, which are mainly located at perovskite surfaces, can trigger hysteresis, carrier recombination, and degradation, which diminish the power conversion efficiencies (PCEs) of the resultant cells. This study concerns the stabilization of the α-FAPbI₃ perovskite phase without negatively affecting the spectral features by using 2,3,4,5,6-pentafluorobenzyl phosphonic acid (PFBPA) as a passivation agent. Accordingly, high-quality PSCs are attained with an improved PCE of 22.25 % and respectable cell parameters compared to the pristine cells without the passivation layer. The thin PFBPA passivation layer effectively protects the perovskite layer from moisture, resulting in better long-term stability for unsealed PSCs, which maintain >90 % of the original efficiency under different humidity levels (40-75 %) after 600 h. PFBPA passivation is found to have a considerable impact in obtaining high-quality and stable FAPbI₃ films to benefit both the efficiency and the stability of PSCs.

Efficient and Stable Perovskite Solar Cells Enabled by Dicarboxylic Acid-Supported Perovskite Crystallization

Defect states at surfaces and grain boundaries as well as poor anchoring of perovskite grains hinder the charge transport ability by acting as nonradiative recombination centers, thus resulting in undesirable phenomena such as low efficiency, poor stability, and hysteresis in perovskite solar cells (PSCs). Herein, a linear dicarboxylic acid-based passivation molecule, namely, glutaric acid (GA), is introduced by a facile antisolvent additive engineering (AAE) strategy to concurrently improve the efficiency and long-term stability of the ensuing PSCs. Thanks to the two-sided carboxyl (-COOH) groups, the strong interactions between GA and under-coordinated Pb²⁺ sites induce the crystal growth, improve the electronic properties, and minimize the charge recombination. Ultimately, champion-stabilized efficiency approaching 22% is achieved with negligible hysteresis for GA-assisted devices. In addition to the enhanced moisture stability of the devices, considerable operational stability is achieved after 2400 h of aging under continuous illumination at maximum power point (MPP) tracking.

Structural design considerations of solution-processable graphenes as interfacial materials via a controllable synthesis method for the achievement of highly efficient, stable, and printable planar perovskite solar cells

Solution-processable graphenes (represented by reduced graphene oxides, rGOs) have shown promising abilities as HTLs in perovskite solar cells (PeSCs). However, there has been no attempt to systematically tailor the characteristics of rGOs to the specifications of PeSCs. Furthermore, the applications of rGO HTLs have been limited to the spin-coating system, which is incompatible with roll-to-roll manufacturing. Here, with the aid of a polymer-graphene hybrid structure and a controllable synthesis method, we successfully developed a much more feasible rGO HTL and demonstrated highly efficient, stable, and printable p-i-n planar PeSCs with facile one-step processing. The characteristics of the developed polyacrylonitrile-grafted rGOs (PRGOs) were optimized by varying the synthesis conditions including the γ-radiation intensity (200, 400, and 600 kGy) and the concentration of the acrylonitrile (AN) precursor (2, 4, and 6 wt%). It is revealed that the PRGO synthesized with a lower AN concentration and a higher irradiation intensity (PRGO_2-600) is the most suitable one for PeSC HTL. PRGO_2-600 effectively raises the average power conversion efficiencies (PCEs) of PeSCs by ∼36% compared to those of conventional PeSCs using PEDOT:PSS HTL. The comprehensive investigations confirm that the enhanced device efficiency stems from (1) the favorable interlayer characteristics of the PRGO itself and (2) the well-crystallized perovskite layer grown on the PRGO. In addition to the PCE, thechemically inert PRGOs can also maintain their electrical properties over time and retard the decomposition of perovskite films, thereby prolonging the operation time of PeSCs in the atmosphere. More importantly, the applicability of the PRGO HTL is clearly verified even in the roll-to-roll compatible slot-die coating system, exhibiting comparable performances to those of the spin-coating system.

Spray coating of the PCBM electron transport layer significantly improves the efficiency of p-i-n planar perovskite solar cells

The p-i-n structure for perovskite solar cells has recently shown significant advantages in minimal hysteresis effects, and scalable manufacturing potential using low-temperature solution processing. However, the power conversion efficiency (PCE) of the perovskite p-i-n structure remains low mainly due to limitations using a flat electron transport layer (ETL). In this work, we demonstrate a new approach using spray coating to fabricate the [6,6]-phenyl-C(61)-butyric acid methyl ester (PCBM) ETL. By creating a rough surface, we effectively improve the light trapping properties inside the PCBM ETL. We reveal that the spray coated PCBM can form a cross-linked network, which may facilitate better charge transport and enhance extraction efficiency. By improving the contact between the perovskite film and the PCBM ETL, a reduction in the trap states is observed resulting in a PCE increase from 13% to >17%.

Hysteresis data of planar perovskite solar cells fabricated with different solvents

In this data article, we introduced the hysteresis of planar perovskite solar cells (PSCs) fabricated using dimethylformamide (DMF), gamma-butyrolactone (GBL), methyl-2-pyrrolidinone (NMP), dimethylsulfoxide (DMSO), DMF-DMSO, GBL-DMSO and NMP-DMSO as perovskite precursor solutions according to different scan directions, sweep times, and current stability. The hysteresis analyses of the planar PSCs prepared with a glass-ITO /NiO_X/perovskite /PC₆₁BM/BCP/Ag configuration were measured with Keithley 2400 source meter unit under 100 mW/cm² (AM 1.5 G). The data collected in this article compares the hysteresis of PSCs with different solvents and is directly related to our research article "High-Performance Planar Perovskite Solar Cells: Influence of Solvent upon Performance" (You-Hyun Seo et al., 2017 [1]).

Synergetic effects of solution-processable fluorinated graphene and PEDOT as a hole-transporting layer for highly efficient and stable normal-structure perovskite solar cells

We demonstrate that a bi-interlayer consisting of water-free poly(3,4-ethylenedioxythiophene) (PEDOT) and fluorinated reduced graphene oxide (FrGO) noticeably enhances the efficiency and the stability of the normal-structure perovskite solar cells (PeSCs). With simple and low temperature solution-processing, the PeSC employing the PEDOT + FrGO interlayer exhibits a significantly improved power conversion efficiency (PCE) of 14.9%. Comprehensive investigations indicate that the enhanced PCE is mostly attributed to the retarded recombination in the devices. The minimized recombination phenomena are related to the interfacial dipoles at the PEDOT/FrGO interface, which facilitates the electron-blocking and the higher built-in potential in the devices. Furthermore, the PEDOT + FrGO device shows a better stability by maintaining 70% of the initial PCE over the 30 days exposure to ambient conditions. This is because the more hydrophobic graphitic sheets of the FrGO on the PEDOT further protect the perovskite films from oxygen/water penetration. Consequently, the introduction of composite interfacial layers including graphene derivatives can be an effective and versatile strategy for high-performing, stable, and cost-effective PeSCs.

Efficient promotion of charge separation and suppression of charge recombination by blending PCBM and its dimer as electron transport layer in inverted perovskite solar cells

Admixing PCBM and its dimer as electron transport material significantly improves charge carrier dynamic behavior in inverted perovskite device.