Chen Weijie

Pyridine-based materials are pre-embedded into the PEDOT:PSS HTL, generating an interaction between them. This interaction in the buried interface transport layer significantly influences the transformation process of the perovskite intermediate phase, leading to a high-quality film and consequently facilitating faster charge transfer, as proven by DFT calculations and in situ GIWAXS technology.

Abstract

Quasi-2D perovskites show great potential as photovoltaic devices with superior stability, but the power conversion efficiency (PCE) is limited by poor carrier transport. Here, it is simultaneously affected the hole transport layer (HTL) and the perovskite layer by incorporating pyridine-based materials into poly(3,4-ethylenedioxythiophene): polystyrene sulfonate (PEDOT:PSS) to address the key problem above in 2D perovskites. With this approach, the enhanced optoelectronic performance of the novel PEDOT:PSS is due to electron transfer between the additives and PEDOT or PSS, as well as a dissociation between PEDOT and PSS based on experimental and theoretical studies, which facilitates the charge extraction and transfer. Concurrently, in-situ X-ray scattering studies reveal that the introduction of pyridine-based molecules alters the transformation process of the perovskite intermediate phase, which leads to a preferred orientation and ordered distribution caused by the Pb─N chemical bridge, achieving efficient charge transport. As a result, the pyridine-treated devices achieve an increased short-circuit current density (J _sc) and PCE of over 17%.

The present review aims to analyze the chronological evolution of various research efforts made on the stability in methyl-ammonium (MA), formamidinium (FA), and guanidinium (GA)-based perovskite solar cells (PSCs), emphasizing both inert and open environment conditions. Also, the future challenges and expected solutions in the area of hybrid halide perovskite (HHP)-based solar cells are outlined in this review. It ought to motivate the researchers to seek out and tackle multidisciplinary research issues with PSCs at present. It is expected that up to 2040, the PSCs will replace the extant silicon solar cells due to the advantage of flexibility, low cost production, and high efficiency. Thus, the present review will serve as a milestone to have updated knowledge of PSCs till time and to find the solutions for problems existing in the PSCs at present.

Hybrid halide perovskite (HHP) emerged as an excellent material for upcoming photovoltaic technologies owing to its rapid performance growth just within a decade. Extensive research worldwide is going on HHP due to their unique optical properties, flexible thin-film nature, and simple low-cost solution-based fabrication processes for solar cells. Albeit HHP solar cells exhibit adequate power conversion efficiency (PCE), poor stability impedes its commercial deployment. This review summarizes the major efforts made worldwide to improve the stability of HHP-based solar cells from time to time. Methyl ammonium lead halide (MAPbI₃) has been first used in HHP-based perovskite solar cells (PSCs) but it is more vulnerable to heat and moisture. Further, formamidinium (FA⁺) and guanidinium (GA⁺) ion doping have been adopted as a compositional modification for better structural and environmental stability. The entire work has been categorized into three sub-areas, i.e., MA,; FA, and GA-based HHP solar cells and the comparison of various photovoltaic parameters of these cells has been presented. Furthermore, the challenges and prospects for PSC research and development toward commercialization have also been presented.

The ratio of Sn²⁺ to Sn⁴⁺ significantly influences the SnO₂ film characteristics in perovskite solar cells. The strategic approach, adjusting addition sequences, yields an upgraded SnO₂ film, marked by enhanced electron mobility, extended carrier lifetime, smooth surface, and optimal energy levels. The notable efficiency increases from 22.58% to 24.16% with outstanding excellent long-term stability.

The ratio of Sn²⁺ to Sn⁴⁺ plays an essential role in influencing the characteristics of SnO₂ film, which is commonly used in the normal structure of perovskite solar cells (PSCs). It is identified that different sequences of addition lead to varying concentrations of Sn²⁺ and Sn⁴⁺ within the SnO₂ film. Through this strategic approach, an enhanced SnO₂ film with improved electron transport capabilities, a smoother surface texture, and more suitable energy levels are successfully engineered. Consequently, the efficiency of PSCs has seen a notable increase from 22.58% for the control device to 24.16% for the target PSC. Furthermore, PSCs utilizing the optimized SnO₂ have demonstrated superior long-term environmental stability when compared to the control devices. Specifically, PSCs incorporating optimized SnO₂ expose to approximately 30% humidity in ambient air for 41 days without encapsulation retain 87% of their initial efficiency. In contrast, the control devices under the same conditions only maintain 77% of their original value.

A hole transport material (HTM) (BDT-p-IDN) with edge-on orientation was successfully designed and synthesized through replacing the terminal group from diphenylamine to indoline unit. BDT-p-IDN delivered a comparable power conversion efficiency (PCE) (23.28%) with its face-on orientation counterpart, which indicated HTMs with edge-on orientation are potential candidates for efficient and stable PSCs.

Molecular stacking and orientation are of great importance in regulating optoelectronic properties. Typically, the face-on orientation of hole transporting materials (HTMs) is considered to be a prerequisite for the realization of high efficiency perovskite solar cells (PSCs). Herein, a small molecule HTM, BDT-p-IDN, is developed with edge-on orientation by replacing the terminal group from diphenylamine to indoline unit. Remarkably, the PSCs device based on dopant-free BDT-p-IDN exhibits an efficiency of 23.28%, which is comparable to that of its face-on control BDT-DPA-F. Compared to BDT-DPA-F, BDT-p-IDN has stronger interaction with the perovskite (PVK) film and therefore stronger hole extraction and defect passivation capabilities, resulting in an increased short circuit current density and improved efficiency. The results indicate that edge-on orientation could be a powerful way for HTMs to realize efficient PSCs.

The introduction of benzoyl sulfonyl molecules engaged in interactions with both SnO₂ and perovskite, resulting in successful bilateral passivation and crystallization regulation at buried interface. Consequently, the modified photovoltaic cells exhibited a substantial efficiency boost, increasing from 22.27% to 24.56%, maintaining 90% of their original efficiency even after 500 h of maximum power point tracking.

Abstract

Well-engineered buried interfaces play a pivotal role in achieving high-performance perovskite solar cells (PSCs). A superior buried interface involves controlled perovskite crystallization, efficient charge transfer across interfaces, and robust interfacial bonding. Here, a class of innovative additives, benzoyl sulfonyl molecules including 4-sulfobenzoic acid monopotassium salt (K-SBA), and 4-sulfamoylbenzoic acid (SBA) is introduced to tailer the SnO₂/perovskite buried interface, aiming to meet these essential criteria. Among them, K-SBA performed better. The findings reveal that the functional groups of K-SBA establish interactions with both SnO₂ and perovskite, leading to effective bilateral passivation and mitigation of interface stress. This results in the formation of a pore-free buried interface and high-quality perovskite films with substantial crystal sizes. Consequently, PSCs incorporating K-SBA exhibited a notable increase in efficiency, achieving 24.56% efficiency compared to the control device's 22.27%. Furthermore, these K-SBA-enhanced PSCs maintain 90% of their original efficiency even after 500 h of maximum power point tracking. This work provides valuable insights for further refinement and advancement of buried interfaces in PSCs.

The molecular ordering and phase separation of a stretchable ternary active layer consisting of D18, Y6, and SEBS is finely regulated by additive-assisted sequential deposition. The optimal microstructure enables a high efficiency of 16.54% and a large crack-onset strain of 26.38%. This produces an efficiency-stretchability factor of 4.36%, which is among the best performances in stretchable organic solar cells.

Abstract

Stretchable organic solar cells (OSCs) with high power conversion efficiency and good mechanical deformation are promising as power sources for wearable electronics. However, synergistic improvement of both photovoltaic efficiency and mechanical ductility is challenging for state-of-the-art polymer donor: non-fullerene acceptor (NFA)-based photovoltaic active layers. Here, a high-performance stretchable OSC with a power conversion efficiency of 16.54% and a crack-onset strain of 26.38% by synergetic optimization film microstructure of sequentially deposited ternary active layer consisting of a polymer donor poly[2,6-(4,8-bis(5-(2-ethylhexyl-3-fluoro)thiophen-2-yl)-benzo[1,2-b:4,5-b']dithiophene))-alt-5,5'-(5,8-bis(4-(2-butyloctyl)thiophen-2-yl)dithieno[3',2':3,4;2'',3'':5,6]benzo[1,2-c][1,2,5]thiadiazole)] (D18), an NFA 2,2'-((2Z,2'Z)-((12,13-bis(2-ethylhexyl)-3,9-diundecyl-12,13-dihydro-[1,2,5]thiadiazolo[3,4-e]thieno[2'',3'':4',5']thieno[2',3':4,5]pyrrolo[3,2-g]thieno[2',3':4,5]thieno[3,2-b]indole-2,10-diyl)bis(methanylylidene)bis(5,6-difluoro-3-oxo-2,3-dihydro-1H-indene-2,1-diylidene))dimalonitrile) (Y6), and an elastomer polystyrene-block-poly(ethylene-ran-butylene)-block-polystyrene (SEBS) is reported. Adding a low-content solvent additive para-xylene into main solvent carbon disulfide induces high-density fibers networks with low crystallinity in bottom D18 layer, and this further suppresses the large phase separation between Y6 and SEBS in top layer. Moreover, incorporating a solid additive 1,3-dibromo-5-chlorobenzene with better compatibility with Y6 can promote Y6 dispersions to form smaller ordered domains in SEBS matrix. Finally, the optimal ternary active layer shows significantly higher efficiency and stretchability, resulting in a large efficiency-stretchability factor of 4.36%, which is among the best values for stretchable OSCs.

A structural and chemical crosslinking interface is proposed and constructed by introducing an extra layer, which blends SnO₂ nanoparticles with chloride salts. It leads to preferable energy level alignment and the improved quality of SnO₂ and perovskite films. Consequently, 98% of initial efficiencies are maintained after 10 000 h, and an efficiency of 25.28% is achieved with 1.53 eV perovskite.

Abstract

Due to the limited interface contact and weak interfacial interaction, planar heterojunction perovskite solar cells (PSCs) have space for further improvement. Herein, a structural and chemical crosslinking interface is proposed and constructed by introducing an extra layer, which blends tin dioxide (SnO₂) nanoparticles with chloride salts. Since the incorporated materials can be dissolved during the fabrication of perovskite, the quality of perovskite films is improved, leading to larger grain size and reduced trap-state density. Also, more chloride ions at the SnO₂/perovskite interface are observed and the interaction between Cl⁻ and Sn⁴⁺ is confirmed. It results in more pronounced n-type SnO₂ with better conductivity and deeper conduction bands, leading to preferable energy level alignment between SnO₂ and perovskite. Consequently, the open-circuit voltage and fill factor of the devices increase, and target cells present better stability, retaining 98% of initial efficiencies after >10 000 h storage in dry air (≈5% relative humidity) and maintaining 85.50% of the initial efficiency after 1000 h of operation under light. This strategy enables the achievement of 25.28% efficiency with a low bandgap (1.53 eV) perovskite composition, and it is confirmed to be universal when other related materials are utilized.

An effective strategy to enhance the miscibility between the conjugated polymer PM6 and the insulating elastomer styrene-butadiene-styrene (SBS) has been developed by incorporating carboxyl groups into SBS (SBS-COOH), resulting in optimized mechanical properties and morphology of PM6. A remarkable power conversion efficiency of 19.04% is achieved for organic solar cells with 5% SBS-COOH (PM6:L8-BO system), outperforming devices of PM6:L8-BO without or with SBS.

Abstract

Incorporating flexible insulating polymers is a straightforward strategy to enhance the mechanical properties of rigid conjugated polymers, enabling their use in flexible electronic devices. However, maintaining electronic characteristics simultaneously is challenging due to the poor miscibility between insulating polymers and conjugated polymers. This study introduces the carboxylation of insulating polymers as an effective strategy to enhance miscibility with conjugated polymers via surface energy modulation and hydrogen bonding. The carboxylated elastomer, synthesized via a thiol-ene click reaction, closely matches the surface energy of the conjugated polymer. This significantly improves the mechanical properties, achieving a high crack-onset strain of 21.48%, surpassing that (5.93%) of the unmodified elastomer:conjugated polymer blend. Upon incorporating the carboxylated elastomer into PM6:L8-BO-based organic solar cells, an impressive power conversion efficiency of 19.04% is attained, which top-performs among insulating polymer-incorporated devices and outperforms devices with unmodified elastomer or neat PM6:L8-BO. The superior efficiency is attributed to the optimized microstructures and enhanced crystallinity for efficient and balanced charge transport, and suppressed charge recombination. Furthermore, flexible devices with 5% carboxylated elastomer exhibit superior mechanical stability, retaining ≈88.9% of the initial efficiency after 40 000 bending cycles at a 1 mm radius, surpassing ≈83.5% for devices with 5% unmodified elastomer.

An oriented molecular bridge is proposed to construct homogeneous buried interface and enhance interfacial carrier transport. The resulting perovskite solar cells (PSCs) with an active area of 0.08 cm² and 1 cm² obtain PCEs of 25.32% (certified PCE: 25.32%) and 24.20%, respectively. In addition, the PSCs with oriented molecular bridge also exhibit excellent stability.

Abstract

Buried interface optimization matters the efficiency improvement of planar perovskite solar cells (PSCs), and the molecular bridge is reported to be an effective approach. Herein, a molecular bridge is constructed at buried interface using 4-chloro-3-sulfamoylbenzoic acid (CSBA), and its preferred arrangement is systematically investigated. It is elucidated that the CSBA molecular is prone to be orientationally absorbed on TiO₂ surface through COOH–Ti, and then connect with perovskite through S═O–Pb, resulting in a feasible oriented molecular bridge. Contributing to the passivated interfacial defects, optimized interfacial energy level, and released perovskite tensile stress, resulting from the oriented CSBA molecular bridge, the PSCs with an active area of 0.08 cm² achieve a certified power conversion efficiency (PCE) of 25.32%, the highest among the TiO₂-based planar PSCs. Encouragingly, the PSCs with an active area of 1 cm² achieve a champion PCE of 24.20%, significantly promoting the efficiency progress of large-area PSCs. In addition, the PSCs with oriented CSBA molecular bridge possess enhanced stability, the unencapsulated PSCs can maintain ≈91% and ≈85% of their initial PCE after 3000 h aging under ambient condition and 1200 h aging under exposure to UV irradiation.

The surface crystallization modulation technique is introduced to fabricate the high-quality 2D perovskite films with both vertical crystal orientation and high phase purity by regulating the crystallization dynamics. The solvent atmosphere condition is instituted during film processing, which promotes the formation of an oriented 2D perovskite layer at the vapor–liquid interface and templates the subsequent film growth.

Abstract

2D perovskites have shown great potential toward stable and efficient photovoltaic devices. However, the crystal orientation and phase impurity issues of 2D perovskite films originating from the anisotropic crystal structure and specific growth mechanism have demoted their optoelectronic performances. Here, the surface crystallization modulation technique is introduced to fabricate the high-quality 2D perovskite films with both vertical crystal orientation and high phase purity by regulating the crystallization dynamics. The solvent atmosphere condition is instituted during film processing, which promotes the formation of an oriented 2D perovskite layer in stoichiometric composition at the vapor–liquid interface and templates the subsequent film growth. The solar cells based on the optimized 2D perovskite films exhibit a power conversion efficiency of 15.04%, the record for 2D perovskites (with the perovskite slab thickness n ≤ 3 and high phase purity). The solar cells based on the highly-oriented and phase-pure 2D perovskite films also demonstrate excellent thermal and humidity stabilities.

The ternary strategy has attracted tremendous interest due to its versatile advantages for improving the performance of organic solar cells. In this work, two polymer donors based ternary organic solar cells are prepared to achieve both high power conversion efficiency (over 19%) and long thermal stability. This study proposes the collaborative regulation of two critical driving forces mechanisms for constructing high-performance ternary organic solar cells.

Abstract

Ternary strategyopens a simple avenue to improve the power conversion efficiency (PCE) of organic solar cells (OSCs). The introduction of wide bandgap polymer donors (PDs) as third component canbetter utilize sunlight and improve the mechanical and thermal stability of active layer. However, efficient ternary OSCs (TOSCs) with two PDs are rarely reported due to inferior compatibility and shortage of efficient PDs match with acceptors. Herein, two PDs-(PBB-F and PBB-Cl) are adopted in the dual-PDs ternary systems to explore the underlying mechanisms and improve their photovoltaic performance. The findings demonstrate that the third components exhibit excellent miscibility with PM6 and are embedded in the host donor to form alloy-like phase. A more profound mechanism for enhancing efficiency through dual mechanisms, that are the guest energy transfer to PM6 and charge transport at the donor/acceptor interface, has been proposed. Consequently, the PM6:PBB-Cl:BTP-eC9 TOSCs achieve PCE of over 19%. Furthermore, the TOSCs exhibit better thermal stability than that of binary OSCs due to the reduction in spatial site resistance resulting from a more tightly entangled long-chain structure. This work not only provides an effective approach to fabricate high-performance TOSCs, but also demonstrates the importance of developing dual compatible PD materials.

Publication date: June 2024

Source: Journal of Energy Chemistry, Volume 93

Author(s): Xiaojing Lv, Weisheng Li, Jin Zhang, Yujie Yang, Xuefei Jia, Yitong Ji, Qianqian Lin, Wenchao Huang, Tongle Bu, Zhiwei Ren, Canglang Yao, Fuzhi Huang, Yi-Bing Cheng, Jinhui Tong

Publication date: June 2024

Source: Journal of Energy Chemistry, Volume 93

Author(s): You Liu, Lishuang Zheng, Kuanxiang Zhang, Kun Xu, Weicheng Xie, Jue Zhang, Yulu Tian, Tianyuan Liu, Hanzhong Xu, Ruoming Ma, Wei Huang, Jiahui Chen, Jusheng Bao, Chen Chen, Yongsheng Zhou, Xuchun Wang, Junming Chen, Jungan Wang

Publication date: May 2024

Source: Journal of Energy Chemistry, Volume 92

Author(s): Sun-Ju Kim, YeonJu Kim, Ramesh Kumar Chitumalla, Gayoung Ham, Thanh-Danh Nguyen, Joonkyung Jang, Hyojung Cha, Jovana Milić, Jun-Ho Yum, Kevin Sivula, Ji-Youn Seo

Publication date: April 2024

Source: Nano Energy, Volume 122

Author(s): Jintian Li, Shilei Ji, Hudie Wei, Jiaqi Gong, Weiwei Mao, Wenjun Zhang, Lei Shi, Xing’ao Li, Liang Chu

Polyvinyl pyrrolidone (PVP) blending has brought a kind of “confinement effect” to PbI₂. Such effects prevent the crystallization of PbI₂ and produces amorphous PbI₂ matrix, and hence reduce the diffuse/reaction barrier between PbI₂ and organic salt, which favors the crystallization of perovskite. The study enlarges the scope of the “confinement effect” of polymers (like PVP) to four aspects: i) flattening the film; ii) retarding fast growth of the host; iii) passivating defect at grain/crystallite boundaries and improving thermal stability of PVSK; iv) retarding ion migration in PVSK.

Abstract

Polyvinyl pyrrolidone is blended in PbI₂ with varied concentration, so as to study the coarsening dynamics of perovskite during the two-step growth method. It is observed that polyvinyl pyrrolidone hinders the crystallization of PbI₂ and helps to form a more amorphous PbI₂ matrix, which then improves perovskite crystallization. As the blending concentration increases from 0 to 2 mM, average crystallite/grain size of perovskite increases from 40.29 nm/0.79 µm to 84.35 nm/1.02 µm while surface fluctuation decreases slightly from 25.64 to 23.96 nm. The observations are caused by the “confinement effect” brought by polyvinyl pyrrolidone on PbI₂. Elevating blending concentration of polyvinyl pyrrolidone results in smaller PbI₂ crystallites and more amorphous PbI₂ matrix, thus reducing the diffusion/reaction barrier between PbI₂ and organic salt and favoring perovskite crystallization. As blending concentration increases from 0 to 2 mM, the device efficiency rises from 19.76 (± 0.60) % to 20.50 (± 0.89) %, with the optimized value up to 22.05%, which is further improved to 24.48% after n-Octylammonium iodide (OAI)-basing surface modification. The study enlarges the scope of “confinement effect” brought by polymer molecules, which is beneficial for efficient and stable perovskite solar cell fabrication.

Tin oxide (SnO₂)-based organic solar cells (OSCs) face challenges such as numerous suface defects and an energy-level mismatch between the work function of SnO₂ and the lowest unoccupied molecular orbital (LUMO) level of Y-series nonfullerene acceptors (NFAs), limiting their power conversion efficiencies (PCEs). This study proposes blending urea-functionalized polyethyleneimine (PEI) with SnO₂ to enhance PCEs and stability of Y-series NFA-based OSCs.

Because of its high conductivity, wide bandgap, and excellent photostability, tin oxide (SnO₂) has long been recognized as an electron-transport layer (ETL) in organic solar cells (OSCs). However, the energy-level mismatch between the work function (WF) of SnO₂ and the lowest unoccupied molecular orbital level of Y-series nonfullerene acceptors (NFAs), along with the abundance of surface defects on SnO₂, have limited its widespread application as ETLs in OSCs. Herein, a novel approach utilizing urea-functionalized polyethyleneimine (PEI) materials called u-PEIs for modifying SnO₂ is introduced. This modification, which serves dual purposes of WF modulation and surface-defect passivation, can mitigate the energy barriers of SnO₂/Y-series NFA and increase the conductivity of the SnO₂ film. PM6:Y6-based OSCs with u-PEI-modified SnO₂ (SnO₂:u-PEI) ETLs exhibit a remarkable efficiency of 16%, which significantly exceeds that (13.5%) achieved with bare SnO₂-based OSCs, along with outstanding photo- and thermal stability. This study confirms the efficacy of urea-functionalized PEI for efficient and stable OCSs, paving the way for SnO₂ applications.

An exciplex interface is developed by the designed and synthesized spirobifluorene phosphonate molecules to mitigate V _OC loss in perovskite solar cells. The multi-functional spirobifluorene phosphonate based exciplex interface can promote hole extraction by donor–acceptor interaction, optimize energy band alignment, and reduce defect-induced recombination. A record V _OC reaching 95% of theoretical limit and a high efficiency are achieved.

Abstract

Metal halide perovskite solar cells (PSCs) show significant advancements in power conversion efficiency (PCE). However, the open-circuit voltage (V _OC) of PSCs is limited by interfacial factors such as defect-induced recombination, energy band mismatch, and non-intimate interface contact. Here, an exciplex interface is first developed based on the strategically designed and synthesized two spirobifluorene phosphonate molecules to mitigate V _OC loss in PSCs. The exciplex interface constructed by the intimate contact between the multi-functional molecules and hole transport layer takes the roles to promote the hole extraction by donor–acceptor interaction, passivate coordination-unsaturated Pb²⁺ defects by equipped phosphonate groups, and optimize the energy level alignment. As a result, a record V _OC of 1.26 V with a perovskite bandgap of 1.61 eV is achieved, representing over 95% of theoretical limit. This advancement leads to an increase in PCE from 21.29% to 24.12% and improved stability. The exciplex interface paves the way for addressing the long-standing challenge of V _OC loss and promotes the wider application of PSCs.

The molecular locking strategy is proposed to stabilize top interface by adopting polydentate ligand green biomaterial 2-deoxy-2,2-difluoro-d-erythro-pentafuranous-1-ulose-3,5-dibenzoate (DDPUD) to manipulate the surface and grain boundaries of perovskite films. The ingenious polydentate ligand chelating is translated into reduced interfacial defects, released interfacial stress, and enhanced moisture resistance. The DDPUD-modified device achieves an enhancement in power conversion efficiency (PCE) from 23.17% to 24.47%.

Abstract

The instability of top interface induced by interfacial defects and residual tensile strain hinders the realization of long-term stable n–i–p regular perovskite solar cells (PSCs). Herein, one molecular locking strategy is reported to stabilize top interface by adopting polydentate ligand green biomaterial 2-deoxy-2,2-difluoro-d-erythro-pentafuranous-1-ulose-3,5-dibenzoate (DDPUD) to manipulate the surface and grain boundaries of perovskite films. Both experimental and theoretical evidence collectively uncover that the uncoordinated Pb²⁺ ions, halide vacancy, and/or I─Pb antisite defects can be effectively healed and locked by firm chemical anchoring on the surface of perovskite films. The ingenious polydentate ligand chelating is translated into reduced interfacial defects, increased carrier lifetimes, released interfacial stress, and enhanced moisture resistance, which should be liable for strengthened top interface stability and inhibited interfacial nonradiative recombination. The universality of the molecular locking strategy is certified by employing different perovskite compositions. The DDPUD modification achieves an enhanced power conversion efficiency (PCE) of 23.17–24.47%, which is one of the highest PCEs ever reported for the devices prepared in ambient air. The unsealed DDPUD-modified devices maintain 98.18% and 88.10% of their initial PCEs after more than 3000 h under a relative humidity of 10–20% and after 1728 h at 65 °C, respectively.

Isomerization of 2,1,3-benzothiadiazole to 1,2,3-benzothiadiazole (iBT) in polymers can concurrently improve photon harvest, suppress nonradiative energy loss, and increase charge mobility. Consequently, the organic solar cells (OSCs) made with polymer PiBT donor and Y6 acceptor achieve efficiency of 19.0%, which is one of the highest efficiencies in binary OSCs. Polymer PiBT does broaden the family of efficient polymer donors.

Abstract

The exploration of high-performance and low-cost wide-bandgap polymer donors remains critical to achieve high-efficiency nonfullerene organic solar cells (OSCs) beyond current thresholds. Herein, the 1,2,3-benzothiadiazole (iBT), which is an isomer of 2,1,3-benzothiadiazole (BT), is used to design wide-bandgap polymer donor PiBT. The PiBT-based solar cells reach efficiency of 19.0%, which is one of the highest efficiencies in binary OSCs. Systemic studies show that isomerization of BT to iBT can finely regulate the polymers’ photoelectric properties including i) increasing the extinction coefficient and photon harvest, ii) downshifting the highest occupied molecular orbital energy levels, iii) improving the coplanarity of polymer backbones, iv) offering good thermodynamic miscibility with acceptors. Consequently, the PiBT:Y6 bulk heterojunction (BHJ) device simultaneously reaches advantageous nanoscale morphology, efficient exciton generation and dissociation, fast charge transportation, and suppressed charge recombination, leading to larger V _OC of 0.87 V, higher J _SC of 28.2 mA cm⁻², greater fill factor of 77.3%, and thus higher efficiency of 19.0%, while the analog-PBT-based OSCs reach efficiency of only 12.9%. Moreover, the key intermediate iBT can be easily afforded from industry chemicals via two-step procedure. Overall, this contribution highlights that iBT is a promising motif for designing high-performance polymer donors.

Publication date: 20 March 2024

Source: Joule, Volume 8, Issue 3

Author(s): Miha Kikelj, Laurie-Lou Senaud, Jonas Geissbühler, Florent Sahli, Damien Lachenal, Derk Baetzner, Benjamin Lipovšek, Marko Topič, Christophe Ballif, Quentin Jeangros, Bertrand Paviet-Salomon

This study introduces a novel approach using 3-(1-pyridinio)-1-propanesulfonate (PPS) as an additive in SnO₂ quantum dots synthesis for applications in perovskite solar cells (PSCs). PPS accelerates the synthesis, passivates surface perovskite defects, and improves electron transfer at the SnO₂–perovskite interface, leading to PSCs with reduced hysteresis, suggesting PPS as a cost-effective alternative additive to thiourea.

In recent years, SnO₂ quantum dots (QDs) have been widely used for preparing the electron-transport layer within perovskite solar cells (PSCs). However, the fabricated devices exhibit an evident hysteresis unless interlayer materials are introduced to passivate or prevent the formation of trap states at the SnO₂–perovskite interface. Herein, the use of the zwitterion 3-(1-pyridinio)-1-propanesulfonate (PPS) as additive inside the SnO₂ QDs solution is proposed. The results highlight that the PPS plays a multifunctional role by accelerating the synthesis of the QDs, enhancing the electron transfer and passivating defects at the SnO₂–perovskite interface. The resulting PSCs with SnO₂ QDs incorporating PPS exhibit a remarkable reduction in hysteresis index (HI) compared to those prepared with thiourea or without any additives. This reduction in HI suggests that PPS serves as a cost-effective alternative additive for SnO₂ QDs preparation, eliminating the need for additional interlayers or expensive additives.

The research presents a schematic representation of increased charge transport driven by interfacial engineering and defect passivation techniques. In addition, the insights into the formation of defect states and their impact on device performance are investigated. Notably, the advantages of using buffer and dipole layers for engineering the interfaces are presented.

Finding the most suitable pathways to improve the interfacial charge transportation in lead halide perovskite solar cells is a highly desirable research area to enhance device performance and enable commercialization. The complexities of interfacial charge dynamics, encompassing separation, diffusion, and collection processes, pivot on the thoughtful selection of interlayers and their inherent properties. Challenges arise from nonideal interfaces characterized by mismatched energy levels and defects that hinder efficient charge transport. To address these concerns, implementing tailored interfacial engineering strategies, including interlayer modification, band alignments, and passivation techniques, can help mitigate unwanted nonradiative recombination. This review aims to elucidate the impact of trap states on suppressing charge transport in the device, along with subsequent passivation techniques designed to enhance interfacial charge transport. Following that, a comprehensive overview is presented, highlighting recent advancements in interface engineering techniques that improve interfacial properties between the electron transport layer/perovskite and perovskite/hole transport layer. Significantly, the impact of using buffer and dipole layers as interlayers on overall device performance and stability is investigated.

Machine learning (ML) methods are used to predict the most limiting parameter of perovskite solar cells’ performance, solely based on the current–voltage curve. With simulation tools, 20 different physical parameters related to charge transport and recombination are varied individually. The simulated current–voltage curves are classified by ML for the changed parameter, with accuracies above 80%. Application to reported devices is shown for demonstration.

Herein, it is shown that machine learning (ML) methods can be used to predict the parameter that limits the solar-cell performance most significantly, solely based on the current density–voltage (J–V) curve under illumination. The data (11’150 J–V curves) to train the model is based on device simulation, where 20 different physical parameters related to charge transport and recombination are varied individually. This approach allows to cover a wide range of effects that could occur when varying fabrication conditions or during degradation of a device. Using ML, the simulated J–V curves are classified for the changed parameter with accuracies above 80%, where Random Forests perform best. It turns out that the key parameters, short-circuit current density, open-circuit voltage, maximum power conversion efficiency, and fill factor are sufficient for accurate predictions. To show the practical relevance, the ML algorithms are then applied to reported devices, and the results are discussed from a physics perspective. It is demonstrated that if some specified conditions are met, satisfying results can be reached. The proposed workflow can be used to better understand a device's behavior, e.g., during degradation, or as a guideline to improve its performance without costly and time-consuming lab-based trial-and-error methods.

The PDEDTQ is introduced as the third component into the JD40-BDD20:PA-5 host blend to fabricate the high-performance ternary all-polymer solar cells (all-PSCs) with a power conversion efficiency (PCE) of 18.47%. It can not only transfer energy to JD40-BDD20 and form extra exciton dissociation channels, but also regulate the miscibility between JD40-BDD20 and PA-5 to form a high-quality network with uniform distribution on the micron scale.

Abstract

Herein, efficient ternary all-polymer solar cells (all-PSCs) are fabricated by employing PDEDTQ that possesses down-shifted highest occupied molecular orbital (HOMO) level and blue-shifted absorption with higher maximum absorption coefficients compared with the host donor JD40-BDD20 as a guest donor into the JD40-BDD20:PA-5 host blend. The enhanced light-harvesting and the energy transfer from PDEDTQ to JD40-BDD20 can be observed in the ternary device, which conduces to improving the short circuit current density (J _SC). Additionally, the PDEDTQ shows relatively weak crystalline and well miscibility with the JD40-BDD20, meaning that the morphology can be tuned using the PDEDTQ. Subsequently, a more uniform and fine-divided network with slightly weakened crystalline occurs in the ternary blend film, implying that a more intermixing domain with a higher density of donor/acceptor (D/A) interfaces may be formed. Thus, compared with JD40-BDD20:PA-5, the ternary device obtained enhanced exciton dissociation and charge extraction, reducing charge recombination and energy loss (E _loss). Ultimately, in addition to guaranteeing outstanding fill factor (FF), the higher J _SC and improve open circuit voltage (V _OC) are achieved and then boosted the power conversion efficiency (PCE) from 17.39% to 18.47%, which is one of the highest PCEs for the all-PSCs. Overall, this work provides guidance on forming a high-quality network with uniform distribution of D/A using ternary strategy, and then obtaining high-efficiency all-PSCs processed using non-halogenated solvent.

A novel solid additive is proposed to dual-regulate donor/acceptor diffusion and molecular stacking, thus tuning the spectral response of resulting semi-transparent devices. The weakened visible light absorption intensity and extended utilization of NIR light enable ST-OSCs to simultaneously possess high average visible transmittance and high photocurrent, which results in a record-breaking light utilization efficiency in the AVT range of 40–50%.

Abstract

Semi-transparent organic solar cells (ST-OSCs) possess significant potential for applications in vehicles and buildings due to their distinctive visual transparency. Conventional device engineering strategies are typically used to optimize photon selection and utilization at the expense of power conversion efficiency (PCE); moreover, the fixed spectral utilization range always imposes an unsatisfactory upper limit to its light utilization efficiency (LUE). Herein, a novel solid additive named 1,3-diphenoxybenzene (DB) is employed to dual-regulate donor/acceptor molecular aggregation and crystallinity, which effectively broadens the spectral response of ST-OSCs in near-infrared region. Besides, more visible light is allowed to pass through the devices, which enables ST-OSCs to possess satisfactory photocurrent and high average visible transmittance (AVT) simultaneously. Consequently, the optimal ST-OSC based on PP2+DB/BTP-eC9+DB achieves a superior LUE of 4.77%, representing the highest value within AVT range of 40–50%, which also correlates with the formation of multi-scale phase-separated morphology. Such results indicate that the ST-OSCs can simultaneously meet the requirements for minimum commercial efficiency and plant photosynthesis when integrated with the roofs of agricultural greenhouses. This work emphasizes the significance of additives to tune the spectral response in ST-OSCs, and charts the way for organic photovoltaics in economically sustainable agricultural development.