Tremendous efforts have been dedicated toward minimizing the open-circuit voltage deficits on perovskite solar cells (PSCs), and the fill factors are still relatively low. This hinders their further application in large scalable modules. Herein, we employ a newly designed ammonium salt, cyclohexylethylammonium iodide (CEAI), for interfacial engineering between the perovskite and hole-transporting layer (HTL), which enhanced the fill factor to 82.6% and consequent PCE of 23.57% on the target device. This can be associated with a reduction of the trap-assisted recombination rate at the 3D perovskite surface, via formation of a 2D perovskite interlayer. Remarkably, the property of the 2D perovskite interlayer along with the cyclohexylethyl group introduced by CEAI treatment also determines a pronounced enhancement in the surface hydrophobicity, leading to an outstanding stability of over 96% remaining efficiency of the passivated devices under maximum power point tracking with one sun illumination under N2 atmosphere at room temperature after 1500 h.

Interfacial Passivation Engineering of Perovskite Solar Cells with Fill Factor over 82% and Outstanding Operational Stability on n-i-p Architecture.

Organic–inorganic hybrid perovskite solar cells (PSCs) are promising third‐generation solar cells. They exhibit high power conversion efficiency (PCE) and, in theory, can be manufactured with less energy than several more established photovoltaic technologies, particularly solution‐processed PSCs. Various materials have been widely utilized to modify the buried bottom interface to improve the performance and long‐term stability of PSCs. Here, the latest progress in modifying the buried interface to enhance the performance and stability of PSCs is examined from a materials standpoint, which is classified into inorganic salts, the organic molecular and polymer, carbon materials, perovskite‐related materials, and 2D materials. This material perspective is useful in determining the tactics for achieving the theoretical PCE value of PSCs. It also serves as a solid reference of interface adjustment for other layered structure heterojunction devices.

/pdf/buried-interface-modification-in-perovskite-solar-cells-a-kx2hhtlo.pdf

Buried Interface Modification in Perovskite Solar Cells: A Materials Perspective

Interface engineering and passivating contacts are key enablers to reach the highest efficiencies in photovoltaic devices. While printed carbon–graphite back electrodes for hole‐transporting material (HTM)‐free perovskite solar cells (PSCs) are appealing for fast commercialization of PSCs due to low processing costs and extraordinary stability, this device architecture so far suffers from severe performance losses at the back electrode interface. Herein, a 2D perovskite passivation layer as an electron blocking layer (EBL) at this interface to substantially reduce interfacial recombination losses is introduced. The formation of the 2D perovskite EBL is confirmed through X‐ray diffraction, photoemission spectroscopy, and an advanced spectrally resolved photoluminescence microscopy mapping technique. Reduced losses that lead to an enhanced fill factor and VOC are quantified by electrochemical impedance spectroscopy and JSC–VOC measurements. This enables reaching one of the highest reported efficiencies of 18.5% for HTM‐free PSCs using 2D perovskite as an EBL with a significantly improved device stability.

https://onlinelibrary.wiley.com/doi/pdfdirect/10.1002/aenm.202200837

Employing 2D‐Perovskite as an Electron Blocking Layer in Highly Efficient (18.5%) Perovskite Solar Cells with Printable Low Temperature Carbon Electrode

Contact engineering is a prerequisite for achieving desirable functionality and performance of semiconductor electronics, which is particularly critical for organic–inorganic hybrid halide perovskites due to their ionic nature and highly reactive interfaces. Although the interfaces between perovskites and charge‐transporting layers have attracted lots of attention due to the photovoltaic and light‐emitting diode applications, achieving reliable perovskite/electrode contacts for electronic devices, such as transistors and memories, remains as a bottleneck. Herein, a critical review on the elusive nature of perovskite/electrode interfaces with a focus on the interfacial electrochemistry effects is presented. The basic guidelines of electrode selection are given for establishing non‐polarized interfaces and optimal energy level alignment for perovskite materials. Furthermore, state‐of‐the‐art strategies on interface‐related electrode engineering are reviewed and discussed, which aim at achieving ohmic transport and eliminating hysteresis in perovskite devices. The role and multiple functionalities of self‐assembled monolayers that offer a unique approach toward improving perovskite/electrode contacts are also discussed. The insights on electrode engineering pave the way to advancing stable and reliable perovskite devices in diverse electronic applications.

https://onlinelibrary.wiley.com/doi/pdfdirect/10.1002/adma.202108616

Electrode Engineering in Halide Perovskite Electronics: Plenty of Room at the Interfaces

Surface passivation via post-treatment is an important strategy for improving power conversion efficiency and operational stability of perovskite solar cells. However, so far the interaction mechanisms between passivating additive and perovskite are not well understood. Here, we report the atomic-scale interaction of surface passivating additive 2,2-difluoroethylammonium bromine (2FEABr) on the MAPbI3. It is found that the bulky 2FEA+ cations tend to distribute at film surface, while the Br- anions diffuse from surface into bulk. A combination of 19F, 207Pb, and 2H solid-state NMR further reveal the Br- anions' partial substitution for the I- sites, the restricted motion of partial MA+ cations, and the firmed perovskite lattices, which would improve charge transport and stability of the perovskite films. Optical spectroscopy and ultraviolet photoelectron spectroscopy demonstrate that the 2FEABr induced surface passivation and energetic modification suppress the nonradiative recombination loss. These findings enable the efficiency of the p-i-n structured PSC significantly increasing from 19.44 to 21.06%, accompanied by excellent stability. Our work further establishes more knowledge link between passivating additive and PSC performance. 

/pdf/surface-passivation-and-energetic-modification-suppress-3oij0zhj.pdf

Surface Passivation and Energetic Modification Suppress Nonradiative Recombination in Perovskite Solar Cells

https://onlinelibrary.wiley.com/doi/pdf/10.1002/adfm.202102902

Surface Reconstruction Engineering with Synergistic Effect of Mixed‐Salt Passivation Treatment toward Efficient and Stable Perovskite Solar Cells

The formation of a thin 2D perovskite layer on the surface of 3D perovskite films has become a popular strategy for obtaining a high-efficiency perovskite solar cell (PSC) with an ensured device stability. In this review paper, various experimental methods used for growth of the 2D layer are introduced with the resulting film properties. Furthermore, a variety of organic cation sources for the 2D layer, ranging from alkyl to phenyl ammonium, are explored to investigate their impact on the device stability and photovoltaic performance.

https://www.mdpi.com/1996-1944/13/17/3868/pdf

3D/2D Bilayerd Perovskite Solar Cells with an Enhanced Stability and Performance.

Recently, significant progress has been made in the development of new techniques for the fabrication of mechanically durable, bright, and deformable electroluminescent devices, leading to the emergence of various technologies, such as soft robots, actuators, flexible/stretchable/wearable electronics, and self-healable devices. However, these devices mostly possess coplanar structures, wherein the internally generated light must be transmitted through at least one of the electrodes, and require a thin emissive layer (EML), causing low brightness and less applicability in soft devices. This is particularly challenging in the case of stretchable electroluminescent devices, which require electrodes exhibiting both high transmittance and low resistance even in the stretchable state because thin EMLs have low tolerance to external mechanical deformations. Herein, we report in-plane electric-field-driven, stretchable alternating-current electroluminescent devices with high brightness by utilizing a thick EML comprising multiple parallelly patterned silver nanowires embedded in a zinc-sulfide-embedded polydimethylsiloxane layer. Since the device is driven by an internal in-plane electric field, it can utilize a thick EML without using planar electrodes. At an electric field of 8 V/ μm, the device showed 3.8 times higher electroluminescence luminance than a thin coplanar-structured device and achieved a maximum brightness of 1324 cd/m2 (at 9.12 V/ μm), suggesting that the electric field expands throughout the thick EML. Furthermore, the device exhibited strong mechanoluminescence and good durability of dual-channel luminescence under simultaneous electromechanical stimulation. We believe that our results represent a breakthrough in electroluminescence and mechanoluminescence research and provide important insights into the development of sustainable and stretchable devices with high brightness.

Bright and uniform light emission from stretchable, dual-channel energy conversion systems: Simultaneous harnessing of electrical and mechanical excitations

Cu-doped Ag2BiI5 (Cu:SBI) powders with 0–10 mol% doping concentrations were synthesized by a solid-state method in an evacuated glass tube While Cu doping did not appreciably modify the crystallographic structure or the bandgap of Ag2BiI5 (SBI), it significantly increased light absorption in the wavelength range of 400–700 nm They were applied as light absorbers of n–i–p type solar cells employing mesoporous TiO2 as an electron transporting layer and PTAA as a hole transporting layer, and it was found that Cu doping leads to a notable increase in power conversion efficiency (PCE) Particularly, solar cell devices with 25 mol% Cu-doped SBI (SC-Cu25:SBI) exhibited a PCE of 253% with a VOC of 619 mV, JSC of 713 mA cm−2 and FF of 5725%, which was increased by 25% compared with that of a bare SBI device (PCE = 204%) The PCE increase was mainly due to the significant increase in JSC, suggesting that the enhancement is caused by the increase in light absorption The effect of Cu dopants on the light absorption properties was investigated by first-principles calculations of energy band structures, and charge transport and recombination behaviors of Cu25:SBI were analyzed by transient absorption spectroscopy Under high humidity conditions, SBI shows much better long-term stability than Pb-perovskites such as methylamine lead iodide, while SC-Cu25:SBI shows comparable stability to the bare SBI-based device, implying that Cu doping does not influence the stability of SBI

Enhancement of the photovoltaic properties of Ag2BiI5 by Cu doping

Surface passivation has become a key strategy for an improvement in power conversion efficiency (PCE) of perovskite solar cells (PSCs) since PSCs experienced a steep increase in PCE and reached a comparably matured point. Recently, surface passivation using a mixed salt of fluorinated alkyl ammonium iodide and formamidinium bromide demonstrated a remarkable improvement in both performance and stability, which can be tuned by the length of the alkyl chain. Nevertheless, the role of the alkyl chain in manipulating surface-limited crystal growth was not fully understood, preventing a further progress in interface control. In this study, we found that the length of the fluorine-substituted alkyl chain governed the crystal formation dynamics by manipulating surface tensions of different crystal orientations. The overall enhancement of the (001) plane, being the most favored, commonly resulted from the surface reformation of the perovskite film regardless of the chain length, while the highly oriented (001) over (111) was monitored with a particular chain length. The enhanced crystal orientation during surface recrystallization was responsible for the low trap density and thus effectively suppressed charge recombination at the interface, resulting in a considerable increase in open-circuit voltage and fill factor.

Hyeon-Seo Choi

Papers

Surface Reconstruction Engineering with Synergistic Effect of Mixed‐Salt Passivation Treatment toward Efficient and Stable Perovskite Solar Cells

3D/2D Bilayerd Perovskite Solar Cells with an Enhanced Stability and Performance.

Bright and uniform light emission from stretchable, dual-channel energy conversion systems: Simultaneous harnessing of electrical and mechanical excitations

Enhancement of the photovoltaic properties of Ag2BiI5 by Cu doping

Oriented Crystal Growth during Perovskite Surface Reconstruction.