Non-radiative Recombination Losses Research Articles

Multi‐Selenophene Strategy Enables Dimeric Acceptors‐Based Organic Solar Cells with over 18.5% Efficiency

AbstractDimeric acceptor (DMA) becomes a promising alternative to small‐molecular and polymeric acceptor‐based organic solar cells (OSCs) due to its well‐defined chemical structure, high batch‐to‐batch reproducibility, and low molecular diffusion properties. However, DMAs usually exhibit blueshifted absorptions, limiting their photon utilization abilities. Herein, multi‐selenophene strategies are adopted to develop redshifted DMAs. From monomer (YSe) to dimers (DYSe‐1 and DYSe‐2), reduced electron reorganization energies and exciton binding energies enable the efficient charge dynamics in the DMAs‐based OSCs. Together with their effective absorption extending to ≈920 nm, DYSe‐1‐ and DYSe‐2‐ based OSCs exhibit outstanding short‐circuit current densities (JSCs) over 27 mA cm−2, which are the best among DMAs. Besides, compared with the YSe‐based device, both DMA‐based devices have higher electroluminescence quantum efficiencies and thus reduce nonradiative recombination loss (ΔE3), contributing to their reduced energy losses. The resultant open‐circuit voltages (VOCs) of DYSe‐1‐ and DYSe‐2‐ based OSCs are ≈0.88 V, which, combining their super JSC values, lead to the promising power conversion efficiencies of 18.56% and 18.22%, respectively. These results are among the best in DMAs‐based OSCs and highlight the great potential of the multi‐selenophene strategy for the development of redshifted DMAs with high performance.

Enhanced Efficiency and Stability of Inverted Perovskite Solar Cells via Primary Amine Molecular Reaction.

The inverted perovskite solar cells have drawn considerable attention owing to their low cost, good compatibility, and easy production processes. However, the device performance is still limited by some important factors, such as surface imperfections and interfacial nonradiative recombination losses. Here, N-acetylethylenediamine (N-AE) is introduced to bind to the surface of the perovskite film via an ammonia condensation reaction. This process creates a stable interfacial layer with n-type doping to enhance the open-circuit voltage (VOC). Moreover, during post-treatment, N-AE dissolves a portion of the perovskite on the surface, leading to perovskite recrystallization. This process enhances the surface quality of the perovskite film and reduces nonradiative recombination. As a result, the inverted perovskite solar cell exhibits a power conversion efficiency approaching 20%, with a rise in VOC from 0.96 to 1.05 V. More impressively, the unencapsulated devices display excellent stability at 85 °C annealing and retained 88% of the initial PCE for 816 h.

Modulation on electrostatic potential to build a firm bridge at NiOx/perovskite interface for efficient and stable perovskite solar cells

The NiOx/perovskite interface in NiOx-based inverted perovskite solar cells (PSCs) is one of the main issues that restrict device performance and long-term stability, as the unwanted interfacial defects and undesirable redox reactions cause severe interfacial non-radiative recombination and open-circuit voltage (Voc) loss. Herein, a series of self-assembled molecules (SAMs) are employed to bind, bridge, and stabilize the NiOx/perovskite interface by regulating the electrostatic potential. Based on systematically theoretical and experimental studies, 4-pyrazolecarboxylic acid (4-PCA) is proven as an efficient molecule to simultaneously passivate the NiOx and perovskite surface traps, release the interfacial tensile stress as well as quench the detrimental interface redox reactions, thus effectively suppressing the interfacial non-radiative recombination and enhancing the quality of perovskite crystals. Consequently, the PSCs with 4-PCA treatment exhibited an eminently increased Voc, leading to a significant increase in power conversion efficiency from 21.28% to 23.77%. Furthermore, the unencapsulated devices maintain 92.6% and 81.3% of their initial PCEs after storing in air with a relative humidity of 20%–30% for 1000 h and heating at 65 °C for 500 h in a N2-filled glovebox, respectively.

Optimization of the performance of CsPbI2Br perovskite solar cells in air by adding polyethylene-graft-maleic anhydride and its mechanism

In this study, by adding Polyethylene-graft-maleic anhydride (PGMA) to the inorganic CsPbI2Br perovskite film, the coordination bonds and hydrogen bonds between PGMA and CsPbI2Br cooperate to passivate defects, regulate energy level and stabilize the perovskite structure and eventually improve the device performance. We systematically study the effects of PGMA addition on the morphology, structure, light absorption, defect concentration and carrier lifetime, hydrophobicity, and optical stability and room temperature black phase stability of CsPbI2Br films, and the photoelectric performance and air stability of PSCs, as well as their mechanism. The experimental results show that the addition of 3 wt% of PGMA greatly improves the photoelectric conversion efficiency (PCE) of CsPbI2Br PSCs by 40.19 % because of the synergistic passivation effects and energy level tuning. The hydrogen bonds between –CH2 in PGMA and I−/Br− in CsPbI2Br, along with the coordination of carbonyl groups with Cs+/Pb2+, improve carrier transport and collection by inactivating flaw and managing the level, reducing the non-radiative recombination losses. In addition, the PSCs with 3 wt% of PGMA maintain 80 % of their initial efficiency even after 600 h in high humidity air environment due to the synergistic effect of coordination bonds and hydrogen bonds. Our study provides valuable insights into the use of PGMA to improve the performance of all-inorganic CsPbI2Br PSCs and the practicality of perovskite solar cells.

Interfacial Heterojunction Enables High Efficient PbS Quantum Dot Solar Cells.

Colloidal quantum dots (CQDs) are promising optoelectronic materials for solution-processed thin film optoelectronic devices. However, the large surface area with abundant surface defects of CQDs and trap-assisted non-radiative recombination losses at the interface between CQDs and charge-transport layer limit their optoelectronic performance. To address this issue, an interface heterojunction strategy is proposed to protect the CQDs interface by incorporating a thin layer of polyethyleneimine (PEIE) to suppress trap-assisted non-radiative recombination losses. This thin layer not only acts as a protective barrier but also modulates carrier recombination and extraction dynamics by forming heterojunctions at the buried interface between CQDs and charge-transport layer, thereby enhancing the interface charge extraction efficiency. This enhancement is demonstrated by the shortened lifetime of carrier extraction from 0.72 to 0.46ps. As a result, the resultant PbS CQD solar cells achieve a power-conversion-efficiency (PCE) of 13.4% compared to 12.2% without the heterojunction.

Buried interface modification and light outcoupling strategy for efficient blue perovskite light-emitting diodes

Perovskite light-emitting diodes (PeLEDs) exhibit remarkable potential in the field of displays and solid-state lighting. However, blue PeLEDs, a key element for practical applications, still lag behind their green and red counterparts, due to a combination of strong nonradiative recombination losses and unoptimized device structures. In this report, we propose a buried interface modification strategy to address these challenges by focusing on the bottom-hole transport layer (HTL) of the PeLEDs. On the one hand, a multifunctional molecule, aminoacetic acid hydrochloride (AACl), is introduced to modify the HTL/perovskite interface to regulate the perovskite crystallization. Experimental investigations and theoretical calculations demonstrate that AACl can effectively reduce the nonradiative recombination losses in bulk perovskites by suppressing the growth of low-n perovskite phases and also the losses at the bottom interface by passivating interfacial defects. On the other hand, a self-assembly nanomesh structure is ingeniously developed within the HTLs. This nanomesh structure is meticulously crafted through the blending of poly-(9,9-dioctyl-fluorene-co-N-(4-butyl phenyl) diphenylamine) and poly (n-vinyl carbazole), significantly enhancing the light outcoupling efficiency in PeLEDs. As a result, our blue PeLEDs achieve remarkable external quantum efficiencies, 20.4% at 487 nm and 12.5% at 470 nm, which are among the highest reported values. Our results offer valuable insights and effective methods for achieving high-performance blue PeLEDs.

Highly Efficient and Scalable p-i-n Perovskite Solar Cells Enabled by Poly-metallocene Interfaces.

Inverted p-i-n perovskite solar cells (PSCs) are easy to process but need improved interface characteristics with reduced energy loss to prevent efficiency drops when increasing the active photovoltaic area. Here, we report a series of poly ferrocenyl molecules that can modulate the perovskite surface enabling the construction of small- and large-area PSCs. We found that the perovskite-ferrocenyl interaction forms a hybrid complex with enhanced surface coordination strength and activated electronic states, leading to lower interfacial nonradiative recombination and charge transport resistance losses. The resulting PSCs achieve an enhanced efficiency of up to 26.08% for small-area devices and 24.51% for large-area devices (1.0208 cm2). Moreover, the large-area PSCs maintain >92% of the initial efficiency after 2000 h of continuous operation at the maximum power point under 1-sun illumination and 65 °C.

Dual Defect Passivation at the Buried Interface for Printable Mesoscopic Perovskite Solar Cells with Reduced Open-Circuit Voltage Loss.

Numerous defects exist at the buried interface between the perovskite and adjacent electron transport layers in perovskite solar cells, resulting in severe non-radiative recombination and excessive open-circuit voltage (VOC) loss. Herein, a dual defect passivation strategy utilizing guanidine sulfate (GUA2SO4) as an interface modifier is first reported. On the one hand, the SO4 2- preferentially interacts with Pb-related defects, generating water-insoluble lead oxysalts complexes. Additionally, GUA+ diffuses into the perovskite and induces the formation of low-dimensional perovskite. These reactions effectively suppress trap states at the buried interface and perovskite boundaries in printable mesoscopic perovskite solar cells (p-MPSCs), thus increasing the carrier lifetime. Meanwhile, GUA2SO4 optimizes the interface energy band alignment, thus accelerating the charge extraction and transfer at the buried interface. This synergistic effect of trap passivation and interface energy band alignment modulation is strongly demonstrated by an increase in average VOC of 70mV and the power conversion efficiency improvement from 17.51% to 18.70%. This work provides a novel approach to efficiently improve the performance of p-MPSCs through dual-targeted defect passivation at the buried interface.

Charge-Transfer States at the Fullerene Interface Cause Nonradiative Recombination Losses in Sn-Based Perovskite Solar Cells

Charge-Transfer States at the Fullerene Interface Cause Nonradiative Recombination Losses in Sn-Based Perovskite Solar Cells

Custom-tailored hole transport layer using oxalic acid for high-quality tin-lead perovskites and efficient all-perovskite tandems.

All-perovskite tandem solar cells (TSCs) have exhibited higher efficiencies than single-junction perovskite solar cells (PSCs) but still suffer from the unsatisfactory performance of low-bandgap (LBG) tin-lead (Sn-Pb) subcells. The inherent properties of PEDOT:PSS are crucial to high-performance Sn-Pb perovskite films and devices; however, the underlying mechanism has not been fully explored and revealed. Here, we report a facile oxalic acid treatment of PEDOT:PSS (OA-PEDOT:PSS) to precisely regulate its work function and surface morphology. OA-PEDOT:PSS shows a larger work function and an ordered reorientation and fiber-shaped film morphology with efficient hole transport pathways, leading to the formation of more ideal hole-selective contact with Sn-Pb perovskite for suppressing interfacial nonradiative recombination losses. Moreover, OA-PEDOT:PSS induces (100) preferred orientation growth of perovskite for higher-quality Sn-Pb films. Last, the OA-PEDOT:PSS-tailored LBG PSC yields an impressive efficiency of up to 22.56% (certified 21.88%), enabling 27.81% efficient all-perovskite TSC with enhanced operational stability.

Regulating the perovskite/C60 interface via a bifunctional interlayer for efficient inverted perovskite solar cells

Inverted perovskite solar cells are promising candidates in photovoltaic fields due to their low-temperature processing, simplified fabrication, and enhanced stability when compared with the conventional configuration. However, the significant non-radiative recombination losses and energy alignment mismatch at the perovskite/C60 interface limit the device's performance and long-term stability. To overcome this drawback, we introduced trifluoromethoxy-functionalized phenethylammonium iodide salts with high polarity between the perovskite and C60 electron transporting layer. This bifunctional interlayer not only effectively passivates the perovskite surface and interface but also reduces the minority carriers through the band rearrangement at this interface, thus significantly suppressing the deteriorating interfacial non-radiative recombination. The modified interlayer also facilitates electron extraction by reducing the offset between the perovskite and C60, contributing to an improved photocurrent and fill factor. The resultant inverted perovskite solar cell based on a Cs0.05FA0.85MA0.10Pb(I0.95Br0.05)3 composition reveals a power conversion efficiency of 24.7 % at the reverse scan and shows negligible efficiency loss after 600 h of maximum power point tracking under one-sun illumination. Overall, this feasible deposition of ammonium-based interlayer establishes a successful demonstration of efficient and stable inverted devices to accelerate the commercialization of perovskite photovoltaics.

Defect passivation and carrier management via a multifunctional additive for efficient and stable wide-bandgap perovskite solar cells with high fill factor

Wide-bandgap (WBG) Methylammonium (MA)-free based perovskite solar cells (PSCs) have attracted widespread research interests due to their broad applicability in multijunction tandem. Nevertheless, the efficiency of WBG PSCs is restricted by unfulfilled potential in fill factor and large deficits in open-circuit voltage. The imbalanced carrier mobility not only plays a critical role in bulk non-radiative recombination loss but also hinders efficient charge collection for mixed I/Br WBG perovskites. Herein, we introduced additive named 2,8-Diiododibenzothiophene to overcome above issues. Inverted devices with enhanced photostability and a record fill factor of 85.7 % are demonstrated. Moreover, combining the semitransparent WBG PSCs with 1.25 eV-bandgap perovskite bottom cells, we realized 4-terminal tandem devices and a champion PCE of 28 % is achieved. The multifunctional additive strategy demonstrated here, will open new avenues for improving WBG PSCs’ performance.

Cross‐layer all‐interface defect passivation with pre‐buried additive toward efficient all‐inorganic perovskite solar cells

AbstractThe buried interface in the perovskite solar cell (PSC) has been regarded as a breakthrough to boost the power conversion efficiency and stability. However, a comprehensive manipulation of the buried interface in terms of the transport layer, buried interlayer, and perovskite layer has been largely overlooked. Herein, we propose the use of a volatile heterocyclic compound called 2‐thiopheneacetic acid (TPA) as a pre‐buried additive in the buried interface to achieve cross‐layer all‐interface defect passivation through an in situ bottom‐up infiltration diffusion strategy. TPA not only suppresses the serious interfacial nonradiative recombination losses by precisely healing the interfacial and underlying defects but also effectively enhances the quality of perovskite film and releases the residual strain of perovskite film. Owing to this versatility, TPA‐tailored CsPbBr3 PSCs deliver a record efficiency of 11.23% with enhanced long‐term stability. This breakthrough in manipulating the buried interface using TPA opens new avenues for further improving the performance and reliability of PSC.

Effect of mild mechanical stresses on device physics of slot-die coated flexible perovskite solar cells

Halide perovskites are a promising class of novel photoactive materials for their application in flexible photovoltaic devices. Tolerance and stability of devices to various mechanical stresses are important aspects of this technology for its effective and long-term operation. Currently, this aspect has not been fully researched and addressed by the research community. Hence, this work is aimed at studying the effect of mild mechanical stresses (MMSs) induced by convex bending on the behaviour of ITO/ZnO/MAPbI3/Spiro-OMeTAD/Au slot-die-coated flexible perovskite solar cells (FPSCs) and investigating the underlying mechanisms leading to performance degradation in devices. The carrier generation, recombination, and extraction processes within FPSCs are investigated before and after the application of MMSs. The obtained results suggest that the photovoltaic performance of the FPSCs deteriorates by up to 50% after convex bending, due to increased non-radiative recombination losses. The results obtained in this work provide some valuable insights into the dynamics of recombination processes in FPSCs exposed to MMSs and can be used for developing new strategies for improving the mechanical stability of devices.

Phosphonic acid based bifunctional additive for high-performance blue perovskite light-emitting diodes

Quasi-two-dimensional (quasi-2D) Ruddlesden-Popper (RP) phase perovskite materials exhibiting quantum confinement effect are promising candidates for realizing high-performance blue perovskite light-emitting diodes (PeLEDs). However, the performance of blue PeLEDs based on quasi-2D perovskites remains unsatisfactory, as it is limited by non-ideal charge transport, energy transfer, and defect. Here, a series of bifunctional phosphonic acid additives with synergistic effects are reported. These additives passivate defects and reduce non-radiative recombination losses by coordinating PO functional group with unsaturated Pb2+, and they promote energy transfer and radiative recombination by optimizing the proportion of small n phases and large n phases. Owing to the synergistic effects of passivation and energy transfer, optimized blue PeLEDs (∼486 nm) with 3-phosphonopropionic acid (3-PA) additive exhibits a champion EQE of 13.11%, which is exceptionally high for blue PeLEDs.

Nanoscale Local Contacts Enable Inverted Inorganic Perovskite Solar Cells with 20.8 % Efficiency.

Inorganic perovskite solar cells (IPSCs) have gained significant attention due to their excellent thermal stability and suitable band gap (~1.7 eV) for tandem solar cell applications. However, the defect-induced non-radiative recombination losses, low charge extraction efficiency, energy level mismatches, and so on render the fabrication of high-efficiency inverted IPSCs remains challenging. Here, the use of 3-amino-5-bromopyridine-2-formamide (ABF) in methanol was dynamically spin-coated on the surface of CsPbI2.85Br0.15 film, which facilitates the limited etching of defect-rich subsurface layer, resulting in the formation of vertical PbI2 nanosheet structures. This enabled localized contacts between the perovskite film and the electron transport layer, suppress the recombination of electron-hole and beneficial to electron extraction. Additionally, the C=O and C=N groups in ABF effectively passivated the undercoordinated Pb2+ at grain boundaries and on the surface of CsPbI2.85Br0.15 film. Eventually, we achieved a champion efficiency of 20.80 % (certified efficiency of 20.02 %) for inverted IPSCs with enhanced stability, which is the highest value ever reported to date. Furthermore, we successfully prepared p-i-n type monolithic inorganic perovskite/silicon tandem solar cells (IPSTSCs) with an efficiency of 26.26 %. This strategy provided both fast extraction and efficient passivation at the electron-selective interface.

Pyrrolidinium Derivative‐Based Ionic Liquid Achieves Defect Passivation for Efficient Perovskite Solar Cells Exceeding 23%

In the rapidly developing field of photovoltaics, organic–inorganic metal halide perovskites are outstanding for their exceptional power conversion efficiencies (PCE), exceeding 26%. However, the full potential of these materials is often undermined by the prevalence of defects within their structure and at the grain surfaces, leading to significant nonradiative recombination losses. To meet this critical challenge, this study introduces a novel strategy involving a pyrrolidinium derivative and tetrafluoroborate ionic liquid, specifically 2‐pyrrolidin‐1‐ium‐1‐ethylammonium tetrafluoroborate (PyE(BF4)2), as an additive in the perovskite precursor. This approach aims to meticulously control crystallization processes and effectively passivate defects on the surface and grain boundaries of the perovskite. The formation of N─H…I− hydrogen bonds and strong ionic interactions, PyE(BF4)2 not only stabilizes the [PbI6]4− framework but also optimizes the valence band alignment with the hole transport layer. Empirical results demonstrate that perovskite solar cells modified with PyE(BF4)2 have achieved a notable PCE of 23.80% and remarkable stability exceeding 1300 h under standard testing protocols (ISOS‐V‐1). The findings emphasize the transformative potential of multifunctional ionic liquids in enhancing the performance and durability of perovskite‐based photovoltaic devices, marking a significant step forward in pursuing sustainable and efficient solar energy solutions.

Regulating Charge Transport Dynamics at the Buried Interface and Bulk of Perovskites by Tailored-phase Two-dimensional Crystal Seed Layer.

Targeting the trap-assisted non-radiative recombination losses and photochemical degradation occurring at the interface and bulk of perovskite, especially the overlooked buried bottom interface, a strategy of tailored-phase two-dimensional (TP-2D) crystal seed layer has been developed to improve the charge transport dynamics at the buried interface and bulk of perovskite films. Using this approach, TP-2D layer constructed by TP-2D crystal seeds at the buried interface can induce the formation of homogeneous interface electric field, which effectively suppress the accumulation of charge carriers at the buried interface. Additionally, the presence of TP-2D crystal seed has a positive effect on the crystallization process of the upper perovskite film, leading to optimized crystal quality and thus promoted charge transport inside bulk perovskites. Ultimately, the best performing PSCs based on TP-2D layer deliver a power conversion efficiency of 24.58 %. The devices exhibit an improved photostability with 88.4 % of their initial PCEs being retained after aging under continuous 0.8-sun illumination for 2000 h in air. Our findings reveal how to regulate the charge transport dynamics of perovskite bulk and interface by introducing homogeneous components.

All-Inorganic Perovskite Solar Cells: Defect Regulation and Emerging Applications in Extreme Environments.

All-inorganic perovskite solar cells (PSCs), such as CsPbX3, have garnered considerable attention recently, as they exhibit superior thermodynamic and optoelectronic stabilities compared to the organic-inorganic hybrid PSCs. However, the power conversion efficiency (PCE) of CsPbX3 PSCs is generally lower than that of organic-inorganic hybrid PSCs, as they contain higher defect densities at the interface and within the perovskite light-absorbing layers, resulting in higher non-radiative recombination and voltage loss. Consequently, defect regulation has been adopted as an important strategy to improve device performance and stability. This review aims to comprehensively summarize recent progresses on the defect regulation in CsPbX3 PSCs, as well as their cutting-edge applications in extreme scenarios. The underlying fundamental mechanisms leading to the defect formation in the crystal structure of CsPbX3 PSCs are firstly discussed, and an overview of literature-adopted defect regulation strategies in the context of interface, internal, and surface engineering is provided. Cutting-edge applications of CsPbX3 PSCs in extreme environments such as outer space and underwater situations are highlighted. Finally, a summary and outlook are presented on future directions for achieving higher efficiencies and superior stability in CsPbX3 PSCs.

Intermediate Phase Suppression with Long Chain Diammonium Alkane for High Performance Wide-Bandgap and Tandem Perovskite Solar Cells.

Wide bandgap (WBG) perovskite can construct tandem cells with narrow bandgap solar cells by adjusting the band gap to overcome the Shockley-Queisser limitation of single junction perovskite solar cells (PSCs). However, WBG perovskites still suffer from severe nonradiative carrier recombination and large open-circuit voltage loss. Here, this work uses an in situ photoluminescence (PL) measurement to monitor the intermediate phase evolution and crystallization process via blade coating. This work reports a strategy to fabricate efficient and stable WBG perovskite solar cells through doping a long carbon chain molecule octane-1,8-diamine dihydroiodide (ODADI). It is found that ODADI doping not only suppresses intermediate phases but also promote the crystallization of perovskite and passivate defects in blade coated 1.67eV WBG FA0.7Cs0.25MA0.05Pb(I0.8Br0.2)3 perovskite films. As a result, the champion single junction inverted PSCs deliver the efficiencies of 22.06% and 19.63% for the active area of 0.07 and 1.02 cm2, respectively, which are the highest power conversion efficiencies (PCEs) in WBG PSCs by blade coating. The unencapsulated device demonstrates excellent stability in air, which maintains its initial efficiency at the maximum power points under constant AM 1.5G illumination in open air for nearly 500h. The resulting semitransparent WBG device delivers a high PCE of 20.06%, and the 4-terminal all-perovskite tandem device delivers a PCE of 28.35%.