Chen Weijie

High-quality (GPA)₂(MA)_n-1Pb_nI_3n+1 film with promoted formation of n = 5 phase, improved crystallinity, preferential vertical growth orientations, reduced trap-state density, and prolonged carrier lifetime is achieved using GPAI as the dimensionality regulator compared to butylamine hydroiodide (BAI). GPA-based PSC exhibits a champion power conversion efficiency of 18.16% that is much superior to the BA-based LDRP PSC (15.43%).

Abstract

Low-dimensional Ruddlesden–Popper phase (LDRP) perovskites are widely studied in the field of photovoltaics due to their tunable energy-band properties, enhanced photostability, and improved environmental stability compared to the 3D perovskites. However, the insulating spacers with weak intramolecular interaction used in LDRP materials limit the out-of-plane charge transport, leading to poor device performance of LDRP perovskite solar cells (PSCs). Here, a functional ligand, 3-guanidinopropanoic acid (GPA), which is capable of forming strong intramolecular hydrogen bonds through the carboxylic acid group, is employed as an organic spacer for LDRP PSCs. Owing to the strong interaction between GPA molecules, high-quality LDRP (GPA)₂(MA)_n-1Pb_nI_3n+1 film with promoted formation of n = 5 phase, improved crystallinity, preferential vertical growth orientations, reduced trap-state density, and prolonged carrier lifetime is achieved using GPAI as the dimensionality regulator compared to butylamine hydroiodide (BAI). As a result, GPA-based LDRP PSC exhibits a champion power conversion efficiency of 18.16% that is much superior to the BA-based LDRP PSC (15.43%). Importantly, the optimized GPA-based LDRP PSCs without encapsulation show enhanced illumination, thermal, storage, and humidity stability compared to BA-based ones. This work provides new insights into producing high n value LDRP films and their efficient and stable PSCs.

A novel inorganic molecule dual interface passivation strategy is designed by introducing non-destructive pure NH₃ gas and potassium tripolyphosphate at the upper and bottom interface. The optimized PSC achieved an excellent power conversion efficiency (PCE) of 24.51%, with significant FF (81.88%) and V_OC (1.229V). This PCE value is the highest reported efficiency for MA-contained PSCs employing gas-passivation so far.

Abstract

The trap states at both the upper and bottom interfaces of perovskite layers significantly impact non-radiative carrier recombination. The widely used solvent-based passivation methods result in the disordered distribution of surface components, posing challenges for the commercial application of large-area perovskite solar cells (PSCs). To address this issue, a novel NH₃ gas-assisted all-inorganic dual-interfaces passivation strategy is proposed. Through the gas treatment of the perovskite surface, NH₃ molecules significantly enhanced the iodine vacancy formation energy (1.54 eV) and bonded with uncoordinated Pb²⁺ to achieve non-destructive passivation. Meanwhile, the reduction of the film defect states is accompanied by a decrease in the work function, which promotes carrier transport between the interface. Further, a stable passivation layer is constructed to manage the bottom interfacial defects using inorganic potassium tripolyphosphate (PT), whose ─P═O group effectively mitigated the charged defects and lowered the carrier transport barriers and nucleation barriers of PVK, while the gradient distribution of K⁺ improved the crystalline quality of PVK film. Based on the dual-interface synergistic effect, the optimal MA-contained PSCs with an effective area of 0.1 cm² achieved an efficiency of 24.51% and can maintain 90% of the initial value after aging (10−20% RH and 20 °C) for 2000 h.

This study introduces a multifunctional potassium trifluoromethyl sulfonate (SK) to modify the chemical bath deposited titanium oxide (TiO₂) electron transport layer and perovskite interface. The modification enhanced the perovskite crystallinity and reduced the non-radiative carrier recombination in perovskite solar cells. As a result, the TiO₂-SK significantly improves the power conversion efficiency (PCE) of FAPbI₃ from 24.01% to 25.22%.

Abstract

The buried interface between the electron transport layer (ETL) and the perovskite layer plays a crucial role in enhancing the power conversion efficiency (PCE) and stability of n–i–p type perovskite solar cells (PSCs). In this study, the interface between the chemical bath deposited (CBD) titanium oxide (TiO₂) ETL and the perovskite layer using multi-functional potassium trifluoromethyl sulfonate (SK) is modified. Structural and elemental analyses reveal that the trifluoromethyl sulfonate serves as a crosslinker between the TiO₂ and the perovskite layer, thus improving the adhesion of the perovskite to the TiO₂ ETL through strong bonding of the ─CF₃ and ─SO₃ ⁻ terminal groups. Furthermore, the multi-functional modifiers reduced interface defects and suppressed carrier recombination in the PSCs. Consequently, devices with a champion PCE of 25.22% and a fill factor (FF) close to 85% is achieved, marking the highest PCE and FF observed for PSCs based on CBD TiO₂. The unencapsulated device maintained 81.3% of its initial PCE after operating for 1000 h.

Carrier transport can be promoted by polarization electric field from BaTiO₃ embedded into the interface of p–n heterojunction of CZTSSe solar cell. As a consequence, the V _oc of CZTSSe solar cell is increased by ca. 40 mV and 20% for power conversion efficiency.

Abstract

The built-in field (E _bi) is a key factor for the dynamic of carrier transport in the heterojunction interface, thus determining the photovoltaic performance of the solar cell, such as Cu₂ZnSn(S,Se)₄ (CZTSSe) cell. It is critical to improve the carriers' transport across the pn heterojunction for the fabrication of highly efficient solar cells. In this work, the large electric field of ferroelectric BaTiO₃ nanoparticles (BTO NPs) is used to tailor the carrier transport in the CZTSSe solar cells by embedding BTO NPs into the interface of CZTSSe/CdS heterojunction. It is very surprising that a polarization electric field (E _P) with the same direction of E _bi synergically enhances carrier transport greatly and increases the PCE by 20.6%. Further study on the mechanism discloses that BTO NPs reduce the work function of CZTSSe and CdS and form interfacial dipoles at their interface, which is conducive to the photogenerated electrons to be collected by the electron transport layer. This strategy also works well on other thin film solar cells and gives a new aspect of strengthening the carrier transport between p–n heterojunction.

A deep-leveled hole transport material TPTI-TPA2F is designed to balance the energy offset at the Cs₂AgBiBr₆/HTM interface, achieving an efficiency of 4.05%.

Abstract

The mismatched energy level alignment at the hole transport interface is recognized to be a prominent limitation for the Cs₂AgBiBr₆-based perovskite solar cell (PSC) to achieve high power conversion efficiency (PCE) but has not been well investigated yet. In order to solve this problem to some extent, it is proposed to balance the energy offset at the Cs₂AgBiBr₆ and hole transport material (HTM) interface to reduce the hole transport barriers, and a novel HTM TPTI-TPA2F with deep level is designed to implement this strategy. The research demonstrates that, on the one hand, the planar π-conjugation and the presence of multiple heteroatoms on TPTI-TPA2F facilitate the formation of well-oriented film and surface defect passivation; on the other hand, the higher film ionization potential of TPTI-TPA2F effectively balances the energy barrier for hole transport. As a result, improved hole-selective contact is achieved with TPTI-TPA2F as HTM, and the interfacial energy loss is suppressed. Correspondingly, the optimized Cs₂AgBiBr₆ PSCs using the TPTI-TPA2F HTM without doped feature an excellent PCE of 4.05% and a high open circuit voltage of 1.15 V, with much improved long-term humidity and thermal stability. This work provides an attractive strategy for developing efficient Cs₂AgBiBr₆ PSCs.

Nature Communications, Published online: 04 July 2024; doi:10.1038/s41467-024-50016-6

Nature Energy, Published online: 04 July 2024; doi:10.1038/s41560-024-01529-3

The issue of low fill factor for M-series acceptor-based organic solar cells (OSCs) has been addressed by delicate morphology control with the layer-by-layer deposition. Meanwhile, increased photocurrent has been achieved by a self-assembled monolayer (2PACz)-based interface engineering for light management within devices. The combined strategies lead to a promising power conversion efficiency of over 18% for the M-series acceptor-based OSCs.

Abstract

M-series molecules are one kind of promising acceptor-donor-acceptor (A-D-A)-type acceptors for constructing high-performance organic solar cells (OSCs). However, their power conversion efficiencies (PCEs) are lagging behind that of current state-of-the-art OSCs, limited by the relatively low fill factor (FF) and photocurrent. Herein, combined strategies of layer-by-layer (LBL) deposition and interface engineering are conducted to systematically improve light utilization and thus PCEs for M36-based OSCs. Through choosing a proper processing solvent, a PCE of 17.3% with an FF of 77.9% is achieved for the resulting LBL devices, much higher than those (15.9%/74.0%) from the blend-casting devices. The improvement is assigned to the favorable morphological evolution that facilitates carrier generation and transport as well as reduces charge recombination. More importantly, light-harvesting of the active layers can be enhanced upon employing a self-assembled monolayer of (2-(9H-carbazol-9-yl)ethyl)phosphonic acid (2PACz) instead of the widely used PEDOT:PSS as the hole-selecting layer, due to the decreased parasitic absorption of the former. Consequently, 2PACz-based LBL devices exhibit significantly increased photocurrent, affording a PCE up to 18.2%, which is the highest among the reported A-D-A-type acceptor-based OSCs. These results deliver important strategies to enhance the performance of OSCs and thus highlight the great potential of M-series acceptors for practical applications.

The complicated trilateral relationships among molecular structures, properties, and photovoltaic performances of electron donor and acceptor materials hinder the rapid improvement of power conversion efficiency (PCE) of organic solar cells (OSCs). Herein, the database of 310 donor and non-fullerene acceptor pairs is constructed and 39 molecular structure descriptors are selected. Four kinds of machine learning (ML) algorithms random forest (RF), extra trees regression, gradient boosting regression trees, and adaptive boosting are applied to predict photovoltaic parameters. The coefficient of determination, Pearson correlation coefficient, mean absolute error, and root mean square error are adopted to evaluate ML performance. The results show that the RF model exhibits the best prediction accuracy. The Gini important analysis suggests the fused ring and aromatic heterocycles are critical fragments in determining PCE. The molecular unit sets are constructed by cutting each donor and acceptor molecules in database. The 31 752 D-π-A-π type donor molecules and 5 455 164 A-π-D-π-A type acceptor molecules are designed by recombination of molecular units, and 173 212 367 328 donor–acceptor pairs are generated by combining the newly designed donor and acceptor molecules. Based on the predicted PCE using the trained RF model, 42 donor–acceptor pairs exhibit the predicted PCE > 16%, in which the highest PCE is 16.24%.

The treatment of FN-O with Lawesson's reagent into FN-S, which converts carbonyl to thiocarbonyl, affects the electronic properties of FN-S. This leads to a stronger interaction between FN-S and the perovskite, providing FN-S with a stronger defect passivation capability, and thus improving the efficiency of PSCs.

Abstract

Organic hole transporting materials (HTMs) are extensively studied in perovskite solar cells (PSCs). The HTMs directly contact the underlying perovskite material, and they play additional roles apart from hole transporting. Developing organic HTMs with defect passivation function has been proved to be an efficient strategy to construct efficient and stable PSCs. In this work, new organic molecules with thiocarbonyl (C═S) and carbonyl (C═O) functional groups are synthesized and applied as HTMs (named FN-S and FN-O). FN-S with C═S can be facilely obtained from FN-O containing C═O. Notably, the C═S in FN-S results in superior defect passivation ability compared to FN-O. Moreover, FN-S exhibits excellent hole extraction/transport capability. Conventional PSCs using FN-S as HTM show an impressive power conversion efficiency (PCE) of 23.25%, with excellent long-term stability and operational stability. This work indicates that simply converting C═O to C═S is an efficient way to improve the device performance by strengthening the defect passivation functionality.

The planarity and compact 2D linear stacking features are attributed to the strong electrostatic potential and intermolecular interactions of the trifluoromethyl group. Devices based on QxIC-CF₃ combine the advantages of the trifluoromethylation and quasiplanar heterojunction (Q-PHJ) devices, resulting in better device stability and a power conversion efficiency (PCE) of 18.1%, the highest efficiency among Q-PHJ devices.

Abstract

Compared to the bulk heterojunction (BHJ) devices, the quasiplanar heterojunction (Q-PHJ) exhibits a more stable morphology and superior charge transfer performance. To achieve both high efficiency and long-term stability, it is necessary to design new materials for Q-PHJ devices. In this study, QxIC-CF₃ and QxIC-CH₃ are designed and synthesized for the first time. The trifluoromethylation of the central core exerts a modulatory effect on the molecular stacking pattern, leveraging the strong electrostatic potential and intermolecular interactions. Compared with QxIC-CH₃, the single crystal structure reveals that QxIC-CF₃ exhibits a more compact 2D linear stacking behavior. These benefits, combined with the separated electron and hole transport channels in Q-PHJ device, lead to increased charge mobility and reduced energy loss. The devices based on D18/QxIC-CF₃ exhibit an efficiency of 18.1%, which is the highest power conversion efficiency (PCE) for Q-PHJ to date. Additionally, the thermodynamic stability of the active layer morphology enhances the lifespan of the aforementioned devices under illumination conditions. Specifically, the T₈₀ is 420 h, which is nearly twice that of the renowned Y6-based BHJ device (T₈₀ = 220 h). By combining the advantages of the trifluoromethylation and Q-PHJ device, efficient and stable organic solar cell devices can be constructed.

Synthesized Y-MOF is introduced, featuring DMA as balanced cations within its pores and strong absorption in UV regime, to modify perovskite. GIWAXS conducted at different angles reveal the predominant bottom distribution of Y-MOF within the perovskite to mitigate the impact of ultraviolet light on the perovskite. Consequently, the Y-MOF-assisted devices to achieve an efficiency of 24.05% with improved UV-light stability.

Abstract

Metal–organic frameworks (MOFs), renowned for their porous and tunable functionalities, hold significant potential for enhancing perovskite photovoltaic. However, the influence of MOF, particularly those with balanced cations in the pores, on the conversion of bottom-layer PbI₂ and the distribution of MOFs within perovskite remains underexplored. Herein, a newly synthesized Yttrium (Y)-MOF material is introduced, featuring dimethylamine (DMA) as balanced cations within its pores and strong absorption in UV regime, to modify perovskite films. Y-MOF, rich in oxygen and nitrogen sites, and featuring DMA within its pores, can passivate uncoordinated Pb²⁺ in perovskite. Scanning electron microscopy (SEM) and grazing incidence wide-angle X-ray scattering (GIWAXS) analysis of the top and bottom surfaces for pristine and Y-MOF-assisted perovskite samples reveal that the presence of PbI₂ in the Y-MOF-assisted perovskite films is negligible. In situ UV–vis analyses demonstrate that the incorporation of Y-MOF decelerates the crystallization kinetics of perovskite, facilitating the development of larger perovskite grains. Moreover, GIWAXS experiments conducted at different angles reveal the predominant bottom distribution of Y-MOF within the perovskite, which effectively mitigates the impact of ultraviolet light on the perovskite. Consequently, the Y-MOF-assisted devices to achieve an efficiency of 24.05% with improved stability especially the UV-light stability.

Two dimerized small-molecule acceptors (DYTVT and DYTCVT) with tailored linker structures are developed. Organic solar cells using DYTVT and DYTCVT as alloy-acceptors exhibit high power conversion efficiency (PCE) of 18.4% and excellent photostability (t _80% lifetime > 4,200 h under 1-Sun illumination).

Abstract

High power conversion efficiency (PCE) and long-term stability are prerequisites for commercialization of organic solar cells (OSCs). Herein, two dimer acceptors (DYTVT and DYTCVT) are developed with different properties through linker engineering, and study their effects as alloy-like acceptors on the photovoltaic performance and photostability of OSCs. These ternary OSCs effectively combine the advantages of both dimer acceptors. DYTVT, characterized by its high backbone planarity, ensures elevated electron mobility and high glass-transition temperature (T _g), leading to efficient charge transport and enhanced photostability of OSCs. Conversely, DYTCVT, with its significant dipole moment and electrostatic potential, enhances compatibility of the alloy acceptors with donors and refines the blend morphology, facilitating efficient charge generation in OSCs. Consequently, D18:DYTVT:DYTCVT OSCs exhibit higher PCE (18.4%) compared to D18:MYT (monomer acceptor, PCE = 16.5%), D18:DYTVT (PCE = 17.4%), and D18:DYTCVT (PCE = 17.0%) OSCs. Furthermore, owing to higher T _g of alloy acceptors (133 °C) than MYT (T _g = 80 °C) and DYTCVT (T _g = 120 °C), D18:DYTVT:DYTCVT OSCs have significantly higher photostability (t _80% lifetime = 4250 h under 1-sun illumination) compared to D18:MYT (t _80% lifetime = 40 h) and D18:DYTCVT OSCs (t _80% lifetime = 2910 h).

A novel π-extended quinoxaline-based acceptor, SMA, is designed and synthesized successfully. SMA possesses highly ordered face-on orientation and strong aggregation propensity. After addition of 10% SMA into the host materials of PM6:BTP-eC9, the ternary devices realize a champion efficiency of 20.22% with optimized morphology, suppressed charge recombination and reduced non-radiative recombination.

Abstract

Organic solar cells, as a cutting-edge sustainable renewable energy technology, possess a myriad of potential applications, while the bottleneck problem of less than 20% efficiency limits the further development. Simultaneously achieving an ordered molecular arrangement, appropriate crystalline domain size, and reduced nonradiative recombination poses a significant challenge and is pivotal for overcoming efficiency limitations. This study employs a dual strategy involving the development of a novel acceptor and ternary blending to address this challenge. A novel non-fullerene acceptor, SMA, characterized by a highly ordered arrangement and high lowest unoccupied molecular orbital energy level, is synthesized. By incorporating SMA as a guest acceptor in the PM6:BTP-eC9 system, it is observed that SMA staggered the liquid-solid transition of donor and acceptor, facilitating acceptor crystallization and ordering while maintaining a suitable domain size. Furthermore, SMA optimized the vertical morphology and reduced bimolecular recombination. As a result, the ternary device achieved a champion efficiency of 20.22%, accompanied by increased voltage, short-circuit current density, and fill factor. Notably, a stabilized efficiency of 18.42% is attained for flexible devices. This study underscores the significant potential of a synergistic approach integrating acceptor material innovation and ternary blending techniques for optimizing bulk heterojunction morphology and photovoltaic performance.

Isomerization engineering is applied to design and synthesize solid additives. Benefiting from optimized molecular stacking and aggregation by isomeric solid additives, M1-treated binary all-small-molecule and polymer organic solar cells (OSCs) yield champion efficiencies of 17.57% and 19.70%, respectively, among the highest power conversion efficiencies of OSCs.

Abstract

Morphology control is crucial in achieving high-performance organic solar cells (OSCs) and remains a major challenge in the field of OSC. Solid additive is an effective strategy to fine-tune morphology, however, the mechanism underlying isomeric solid additives on blend morphology and OSC performance is still vague and urgently requires further investigation. Herein, two solid additives based on pyridazine or pyrimidine as core units, M1 and M2, are designed and synthesized to explore working mechanism of the isomeric solid additives in OSCs. The smaller steric hindrance and larger dipole moment facilitate better π–π stacking and aggregation in M1-based active layer. The M1-treated all-small-molecule OSCs (ASM OSCs) obtain an impressive efficiency of 17.57%, ranking among the highest values for binary ASM OSCs, with 16.70% for M2-treated counterparts. Moreover, it is imperative to investigate whether the isomerization engineering of solid additives works in state-of-the-art polymer OSCs. M1-treated D18-Cl:PM6:L8-BO-based devices achieve an exceptional efficiency of 19.70% (certified as 19.34%), among the highest values for OSCs. The work provides deep insights into the design of solid additives and clarifies the potential working mechanism for optimizing the morphology and device performance through isomerization engineering of solid additives.

Nature Photonics, Published online: 01 July 2024; doi:10.1038/s41566-024-01468-1

By integrating pyrrolidinium thiocyanate (PySCN) into the perovskite precursor, a synchronous regulation strategy is developed to refine film crystallization and minimize trap defects. Utilizing vacuum flash evaporation for perovskite film deposition, large-area perovskite solar cells can achieve an efficiency of 21.15% with increased stability and the self-powered photodetector demonstrates extremely low dark current and superior detection rate.

Abstract

Developing inventive approaches to control crystallization and suppress trap defects in perovskite films is crucial for achieving efficient perovskite photovoltaics. Here, a synchronous regulation strategy is developed that involves the infusion of a zwitterionic ionic liquid additive, pyrrolidinium thiocyanate (PySCN), into the perovskite precursor to optimize the subsequent crystallization and defects. PySCN modification not only orchestrates the crystallization process but also deftly addresses trap defects in perovskite films. Within this, SCN⁻ compensates for positively charged defects, while Py⁺ plays the role of passivating negatively charged defects. Based on the vacuum flash evaporation without anti-solvent, the air-processed perovskite solar cells (PSCs) with PySCN modification can achieve an extraordinary champion efficiency of 22.46% (0.1 cm²) and 21.15% (1.0 cm²) with exceptional stability surpassing 1200 h. Further, the self-powered photodetector goes above and beyond, showcasing an ultra-low dark current of 2.13 × 10⁻¹⁰ A·cm⁻², a specific detection rate of 6.12 × 10¹³ Jones, and an expansive linear dynamic range reaching an astonishing 122.49 dB. PySCN modification not only signifies high efficiency but also ushers in a new era for crystallization regulation, promising a transformative impact on the optoelectronic performance of perovskite-based devices.

This study provides guidelines for the use of efficient ETMs in PSCs, describes the remarkable progress of ETMs in various perovskite systems, and focuses on the key ETL challenges: regulating grain structure, defect passivation techniques, energy level alignment, and interface engineering. It finishes with a detailed assessment of the most advanced ETMs, focusing on their strategic importance and future challenges.

Abstract

Perovskite solar cells (PSCs) stand at the forefront of photovoltaic research, with current efficiencies surpassing 26.1%. This review critically examines the role of electron transport materials (ETMs) in enhancing the performance and longevity of PSCs. It presents an integrated overview of recent advancements in ETMs, like TiO₂, ZnO, SnO₂, fullerenes, non-fullerene polymers, and small molecules. Critical challenges are regulated grain structure, defect passivation techniques, energy level alignment, and interfacial engineering. Furthermore, the review highlights innovative materials that promise to redefine charge transport in PSCs. A detailed comparison of state-of-the-art ETMs elucidates their effectiveness in different perovskite systems. This review endeavors to inform the strategic enhancement and development of n-type electron transport layers (ETLs), delineating a pathway toward the realization of PSCs with superior efficiency and stability for potential commercial deployment.

An effective strategy is developed by designing a bipolar copolymer PM6-b-PYSe as an interlayer between layer-by-layer processed D18 and BTP-eC9 to improve the stretchability of organic solar cells. The copolymer interlayer can shunt the penetration of the upper BTP-eC9 to form desirable phase separation of active layer, favoring enhanced mechanical stretchability and photovoltaic performance of flexible organic solar cells.

Abstract

Mechanical stretchability is a vital criterion for the wearable application of organic solar cells (OSCs), while the excessive rigidity of fused-ring small molecular acceptors make the photovoltaic film hard to meet the stretchable requirements. Herein, an effective strategy is developed to construct an intrinsically stretchable active layer by inserting copolymer PM6-b-PYSe as an interlayer between layer-by-layer processed D18 and BTP-eC9. The copolymer interlayer shunts the penetration of BTP-eC9 and facilitates an appropriate phase separation, favoring the enhanced crack onset strain of 17.69% compared to the D18/BTP-eC9 film (9.67%). Combining with the optimal energy levels, prolonged carrier lifetime, and suppressed bimolecular recombination aroused by the incorporation of PM6-b-PYSe, the D18/PM6-b-PYSe/BTP-eC9-based OSC yields an encouraging efficiency of 17.97%. In particular, the device demonstrates excellent mechanical property, which can retain over 80% after 4000 bending cycles. This work provides an effective strategy to simultaneously enhance the intrinsic mechanical stretchability and photovoltaic performance of flexible OSCs.

Perovskite Solar Cells

In article number 2400078, Yong Hua and co-workers proposed an effective strategy to realize highly efficient and stable perovskite solar cells by the incorporation of a novel organic additive (6BAS) with six anchoring (C═O) groups. 6BAS can promote the preferential crystallization of perovskite to realize high-quality perovskite films, enhance hot carrier transfer and retard the charge carrier recombination in device.

Publication date: November 2024

Source: Journal of Energy Chemistry, Volume 98

Author(s): Liqiang Bian, Zhe Xin, Yuanyuan Zhao, Lei Gao, Zhi Dou, Linde Li, Qiyao Guo, Jialong Duan, Jie Dou, Yingli Wang, Xinyu Zhang, Chi Jiang, Liqing Sun, Qiang Zhang, Qunwei Tang

A remarkable average visible transparency (AVT) of ≈52% is achieved for a semi-transparent organic solar cell. Using a dielectric Bragg reflector as infrared reflecting back electrode, the optimized design reaches a maximum power conversion efficiency (PCE) of 8.79% with an overall light utilization efficiency of up to 4.56%. This approach exemplifies how to overcome the typical trade-off between AVT and PCE.

A crucial challenge in the development of semi-transparent solar cells is to maintain a reasonable power conversion efficiency (PCE) while reaching a high average visible transparency (AVT). Typically, organic semiconductors are favorable for this application since they can selectively absorb infrared light while transmitting visible light. This ability stems from limited electronic states at high(er) energies in contrast to inorganic semiconductors with their typical rise of the absorption coefficient toward higher photon energies. To increase PCE at high AVTs, a series of infrared dielectric Bragg reflectors is developed for semi-transparent organic solar cells. Using the multi-layered back electrode (TiO₂|SiN|TiO₂|AZO|Ag|AZO) with PV-X Plus as photoactive layer and a metal-free PEDOT:PSS top electrode, a light utilization efficiency (LUE = AVT × PCE) of up to 4.32% is achieved, together with an AVT of 47.9%. Although the short circuit current and AVT agree well with optical simulations, a low fill factor (FF) and partial shunting limit the overall device performance. Using ZnO and PFN-Br as additional electron transport layers and modifying the back electrode stack (TiO₂|SiO₂|TiO₂|AZO|Ag|AZO) accordingly leads to an LUE of up to 4.6% with a remarkable AVT of 51.9% and a maximum PCE of 8.79%.

Nature, Published online: 26 June 2024; doi:10.1038/s41586-024-07723-3