Chen Weijie

Publication date: April 2022

Source: Nano Energy, Volume 94

Author(s): Jian He, Jie Su, Jiayu Di, Zhenhua Lin, Siyu Zhang, Jing Ma, Jincheng Zhang, Shengzhong Liu, Jingjing Chang, Yue Hao

Hybrid cathode interlayer composed of PNDIT-F3N:PDIN (0.6:0.4, in wt%) is applied in organic solar cells with PM6:Y6 as the active layer, and a power conversion efficiency of 17.4% is attained, outperforming devices with interlayers such as NDI-M, PDINO, and Phen-DPO. The hybrid strategy is demonstrated as an efficient approach to improve the performance of organic solar cells with nonfullerene acceptors.

Abstract

With the emergence of fused ring electron acceptors, the power conversion efficiency of organic solar cells reached 19%. In comparison with the electron donor and acceptor materials progress, the development of cathode interlayers lags. As a result, charge extraction barriers, interfacial trap states, and significant transport resistance may be induced due to the unfavorable cathode interlayer, limiting the device performances. Herein, a hybrid cathode interlayer composed of PNDIT-F3N and PDIN is adopted to investigate the interaction between the photoexcited acceptor and cathode interlayer. The state of art acceptor Y6 is chosen and blended with PM6 as the active layer. The device with hybrid interlayer, PNDIT-F3N:PDIN (0.6:0.4, in wt%), attains a power conversion efficiency of 17.4%, outperforming devices with other cathode interlayer such as NDI-M, PDINO, and Phen-DPO. It is resulted from enhanced exciton dissociation, reduced trap-assisted recombination, and smaller transfer resistance. Therefore, the hybrid interlayer strategy is demonstrated as an efficient approach to improve device performance, shedding light on the selection and engineering of cathode interlayers for pairing the increasing number of fused ring electron acceptors.

By introducing ClFA⁺ cation to reduce the voltage loss of perovskite front subcell and using chloride substitution to broaden the absorption spectra of organic rear subcell, a monolithic perovskite/organic tandem solar cell is constructed, and the power conversion efficiency reaches 22.0%.

Abstract

Combining the high stability under UV light of the wide bandgap (WBG) perovskite solar cells (pero-SCs) and the broad near-infrared absorption spectra of the narrow bandgap (NBG) organic solar cells (OSCs), the perovskite/organic tandem solar cells (TSCs) with the WBG pero-SC as front cell and the NBG OSC as rear cell have attracted attention . However, the photovoltaic performance of the perovskite/organic TSCs needs to be further improved. Herein, nonradiative charge recombination loss is reduced through bulk defect passivation in the WBG pero-SC front subcell and broadening the range of absorption spectra of the NBG OSC rear cell. For the WBG pero-SCs, an organic cation chloro-formamidinium is introduced into FA_0.6MA_0.4Pb(I_0.6Br_0.4)₃ to passivate the bulk defects in the perovskite film and the WBG pero-SC displays high open-circuit voltage of 1.25 V and high fill factor of 83.0%. For the NBG OSCs, a new infrared-absorbing organic small molecule acceptor BTPV-4Cl-eC9 is designed and synthesized. Then, a monolithic perovskite/organic TSC is fabricated with the WBG pero-SC as the front cell and the NBG OSC as the rear cell, and the TSC demonstrates high power conversion efficiency up to 22.0%. The results indicate that the perovskite/organic TSC is promising for future commercialization.

A π-conjugated ionic multifunctional additive (QAPyBF₄) was developed and introduced into perovskite solar cells (PSCs). QAPyBF₄ passivated defect states in the perovskite layer, adjusted energy level alignment at the perovskite/ETL and perovskite/HTL interfaces, and prevented the decomposition of perovskite crystals. Therefore, a planar PSC with QAPyBF₄ delivered an efficiency of 23.1 % with a remarkable V _oc of 1.2 V and operational stability.

Abstract

Defects and energy offsets at the bulk and heterojunction interfaces of perovskite are detrimental to the efficiency and stability of perovskite solar cells (PSCs). Herein, we designed an amphiphilic π-conjugated ionic compound (QAPyBF₄), implementing simultaneous defects passivation and interface energy level alignments. The p-type conjugated cations passivated the surface trap states and optimized energy alignment at the perovskite/hole transport layer. The highly electronegative [BF₄]⁻ enriched at the SnO₂ interface featured desired band alignment due to the dipole moment of this interlayer. The planar n-i-p PSC had an efficiency of 23.1 % with V _oc of 1.2 V. Notably, the synergy effect elevated the intrinsic endothermic decomposition temperature of the perovskite. The modified devices showed excellent long-term thermal (85 °C) and operational stability at the maximum power point for 1000 h at 45 °C under continuous one-sun illumination with no appreciable efficiency loss.

Nature Energy, Published online: 20 January 2022; doi:10.1038/s41560-021-00966-8

The growth and crystallization of metal halide perovskites are easily manipulated by physical fields, including the electric field, magnetic field, light field, stress field, and thermal field. This review summarizes that these physical fields could regulate perovskite crystals, carrier behaviors, band structures, and phase states, thus affecting the device photovoltaic properties. Accordingly, challenges and prospective research directions are also proposed.

Abstract

With the efforts of researchers from all over the world, metal halide perovskite solar cells (PSCs) have been booming rapidly in recent years. Generally, perovskite films are sensitive to surrounding conditions and will be changed under the action of physical fields, resulting in lattice distortion, degradation, ion migration, and so on. In this review, the progress of physical fields manipulation in PSCs, including the electric field, magnetic field, light field, stress field, and thermal field are reviewed. On this basis, the influences of these fields on PSCs are summarized and prospected. Finally, challenges and prospective research directions on how to make better use of external-fields while minimizing the unnecessary and disruptive impacts on commercial PSCs with high-efficiency and steady output are proposed.

A wide-bandgap double-cable polymer JP02 has an identical absorption spectra with light-emitting diode indoor light, exhibiting a high efficiency of 19.44% in single-component organic solar cells (SCOSCs) that is similar to the bulk-heterojunction (BHJ) system.

Indoor photovoltaic is one of the most important applications of organic solar cells (OSCs). As different from AM1.5G sunlight with broad spectra from the visible to near-infrared region, the spectra of indoor light are usually located in the visible region. Therefore, a special material design for the photoactive layer to meet the requirement of indoor light is required for application in indoor photovoltaics. Herein, a wide-bandgap double-cable conjugated polymer is intentionally selected, which has the well-matched absorption spectra with indoor light for use in indoor OSCs. This double-cable polymer is used as a single photoactive layer in OSCs, providing a high power conversion efficiency of 19.44% under indoor light, which is comparable with the bulk-heterojunction solar cells using near-infrared electron acceptors. Moreover, the double-cable polymer-based indoor OSCs exhibit high storage stability. These results indicate that single-component OSCs based on double-cable polymers have promising applications in indoor OSCs.

The origin of ion migration in organic–inorganic hybrid perovskites (OIHPs) is first reviewed. The ions that may migrate in OHIPs and migrating channels are further discussed in detail. The effects of ion migration on OHIPs are explored and some recently emerged regulation strategies are summarized. A perspective on further inhibition of ion migration in OHIPs is also provided.

Abstract

Organic–inorganic hybrid perovskite (OIHPs) solar cells are the most promising alternatives to traditional silicon solar cells, with a certified power conversion efficiency beyond 25%. However, the poor stability of OHIPs is one of the thorniest obstacles that hinder its commercial development. Among all the factors affecting stability, ion migration is prominent because it is unavoidable and intrinsic in OHIPs. Therefore, it is important to understand the mechanism for ion migration and regulation strategies. Herein, the types of ions that may migrate in OHIPs are first discussed; afterward, the migrating channels are demonstrated. The effects of ion migration are further elaborated. While ion migration can facilitate the p–i–n structure in some cases, the current hysteresis and other adverse effects such as phase segregation in OHIPs attract widespread attention. Based on these, several recent strategies to suppress the ion migration are enumerated, including the introduction of alkali cations, organic additives, grain boundaries passivation, and employment of low-dimensional perovskites. Finally, the prospect for further modulating the ion migration and more stable perovskite solar cells is proposed.

Ternary perovskite–organic solar cells based on 2D:3D perovskites incorporated with n-type low-optical-gap conjugated organic molecules exhibit power conversion efficiency over 23%, and dramatically enhanced stability and diminished photocurrent hysteresis are demonstrated.

Abstract

Perovskite solar cells in which 2D perovskites are incorporated within a 3D perovskite network exhibit improved stability with respect to purely 3D systems, but lower record power conversion efficiencies (PCEs). Here, a breakthrough is reported in achieving enhanced PCEs, increased stability, and suppressed photocurrent hysteresis by incorporating n-type, low-optical-gap conjugated organic molecules into 2D:3D mixed perovskite composites. The resulting ternary perovskite–organic composites display extended absorption in the near-infrared region, improved film morphology, enlarged crystallinity, balanced charge transport, efficient photoinduced charge transfer, and suppressed counter-ion movement. As a result, the ternary perovskite–organic solar cells exhibit PCEs over 23%, which are among the best PCEs for perovskite solar cells with p–i–n device structure. Moreover, the ternary perovskite–organic solar cells possess dramatically enhanced stability and diminished photocurrent hysteresis. All these results demonstrate that the strategy of exploiting ternary perovskite–organic composite thin films provides a facile way to realize high-performance perovskite solar cells.

Highly efficient durable nonfullerene organic solar cells (OSCs) are achieved with a new cathode interlayer based on biradical-forming phenol-functionalized perylene bisimides. These OSCs take advantage of good compatibility between the interlayer material and Y6 electron acceptor dyes and good interlayer thickness tolerance.

Abstract

A new type of cathode interlayer composed of 2,6-di-tert-butyl-phenol-functionalized perylene bisimide (PBI-2P) is successfully applied as an electron transporting layer for fused-ring nonfullerene organic solar cells (OSCs). The stable contact between these novel electron transporting layers and the representative nonfullerene acceptor Y6 greatly enhances the device stability compared to conventional amine-group containing cathode interlayers. Moreover, the easily formed biradical species in the interlayers yields rather good thickness tolerance of the PBI-2P layer in photovoltaic devices. The OSCs based on the PBI-2P interlayer show a power conversion efficiency up to 17.20% and good stability compared to amino-group functionalized interlayers. The findings demonstrate a promising design principle for cathode interlayer engineering based on pigment chromophores equipped with the 2,6-di-tert-butylphenoxy groups that are prone to form the respective ultrastable butylphenoxy radicals for stable nonfullerene OSCs.

Liquid crystal 4((6(acryloyloxy)hexyl)oxy)benzoic acid (6OBA) is introduced as an intelligent temperature-sensitive template to simultaneously enhance the large-scale printability of perovskite inks and the quality of perovskite film for improving the efficiency and mechanical stability of perovskite solar cells (PSCs). The optimized PSCs with 6OBA exhibit superior efficiency of 19.87% for flexible devices (1.01 cm²) and 14.74% for flexible modules (25 cm²).

The control of crystallization and printability of large-area perovskite layers is crucial to facilitating their commercial development in flexible electronics. Considering the benefits of the liquid crystals with intelligent temperature sensitivity for the printable and crystalline template of a scalable perovskite film, a liquid crystal 4((6(acryloyloxy)hexyl)oxy)benzoic acid (6OBA) is introduced. The 6OBA shows a liquid crystal temperature range matching with the thermal annealing temperature of perovskite films. A desire printability of perovskite inks for scalable and homogeneous devices is guaranteed due to the fluidity of the 6OBA additive at room temperature. Moreover, the crystalline 6OBA promotes crystallization of perovskite films during the thermal annealing process, which can also release the residual stress of the whole layer. The optimized perovskite solar cells (PSCs) with 6OBA exhibit superior power conversion efficiency values of 19.87% for flexible devices (1.01 cm²) and 14.74% for flexible modules (25 cm²). The unencapsulated devices can maintain >90% of their original efficiency after 1500 h in the ambient atmosphere. Furthermore, the flexible PSCs exhibit outstanding bending resistance, retaining over 88% of their initial efficiency after 1000 bending cycles at a radius of 3 mm. This work provides a facile strategy for accelerating the development of flexible electronics.

Herein, the possible grain growth mechanism in wetting (PEDOT:PSS) and nonwetting (PEDOT:PSS/PTAA) surfaces is presented. The nonwetting surface facilitates the formation of big perovskite grains, as the crystallization process dominates the nucleation process. In contrast, the reverse happens with wetting surfaces, yielding small-grain perovskite.

Because of their inferior film quality, Pb–Sn-mixed low-bandgap (LBG) perovskites suffer from poor charge transportation, compromising photovoltaic parameters of final solar cells. Herein, an approach to improve the quality of the charge interface layer is proposed, in which a thin layer of hydrophobic [bis (4-phenyl) (2, 4, 6-trimethylphenyl) amine] (PTAA) is inserted between the hole-selective layer of hydrophilic poly (3, 4-ethylenedioxythiophene) -polystyrenesulfonicacid (PEDOT:PSS) and LBG perovskite layer. The introduction of a tiny layer of the hydrophobic PTAA acts as a shield layer to protect the underlying acidic PEDOT:PSS layer from moisture-related degradation and works as an intermediary layer to facilitate the growth of significantly larger perovskite grains; these enlarged grains are indicative of enhanced crystallinity and fewer grain boundaries in the perovskite layer. The fewer grain boundaries lead to suppression of interfacial defects and result in enhanced charge collection at the hole transport layer/perovskite interface, thus improving the open-circuit voltage up to 0.85 V and fill factor up to ≈78%, eventually boosting the power conversion efficiency of the champion cell up to 19.08%. Herein, a simple interface engineering route to fabricate efficient and stable Pb–Sn-mixed LBG perovskite solar cells is offered.

Based on the superior properties of perovskite quantum dots (PQDs) over bulk perovskites, not only the applications of PQDs in perovskite quantum solar cells (PQDSCs), outlining the engineering concerning surface ligands, additives and hybrid composition are reviewed, but also their various roles in other photovoltaic devices, including photo conversion layer, interface layer and additive are presented.

Abstract

Perovskite quantum dots (PQDs) have captured a host of researchers’ attention due to their unique properties, which have been introduced to lots of optoelectronics areas, such as light-emitting diodes, lasers, photodetectors, and solar cells. Herein, the authors aim at reviewing the achievements of PQDs applied to solar cells in recent years. The engineering concerning surface ligands, additives, and hybrid composition for PQDSCs is outlined first, followed by analyzing the reasons of undesired performance of PQDSCs. Subsequently, a novel overview that PQDs are utilized to improve the photovoltaic performance of various kinds of solar cells, is provided. Finally, this review is summarized and some challenges and perspectives concerning PQDs are also discussed.

Fluorine substitution increases the interaction with ZnO and accelerates the photon decomposition of A-D-A type (nonfullerene acceptor) NFA, while he β-alkyl chains on the thiophene unit next to the C═C linker improves the stability of acceptor molecules by forming protecting atomic cage. When using PET-treated ZnO and L8-BO as the electron acceptor, T ₈₀ was estimated over 5000 h.

Abstract

Despite the tremendous efforts in developing non-fullerene acceptor (NFA) for polymer solar cells (PSCs), only few researches are done on studying the NFA molecular structure dependent stability of PSCs, and long-term stable PSCs are only reported for the cells with low efficiency. Herein, the authors compare the stability of inverted PM6:NFA solar cells using ITIC, IT-4F, Y6, and N3 as the NFA, and a decay rate order of IT-4F > Y6 ≈ N3 > ITIC is measured. Quantum chemical calculations reveal that fluorine substitution weakens the C═C bond and enhances the interaction between NFA and ZnO, whereas the β-alkyl chains on the thiophene unit next to the C═C linker blocks the attacking of hydroxyl radicals onto the C═C bonds. Knowing this, the authors choose a bulky alkyl side chain containing molecule (named L8-BO) as the acceptor, which shows slower photo bleaching and performance decay rates. A combination of ZnO surface passivation with phenylethanethiol (PET) yields a high efficiency of 17% and an estimated long T ₈₀ and Ts₈₀ of 5140 and 6170 h, respectively. The results indicate functionalization of the β-position of the thiophene unit is an effective way to improve device stability of the NFA.

A polymer donor PBDF-NS is synthesized by using naphthalene-substituted benzo[1,2-b:4,5-b′]difuran (BDF) and fluorinated benzotriazole units. PBDF-NS possesses a low-lying HOMO level of −5.44 eV and a wide bandgap of 1.87 eV. Enormous progress in efficiency are achieved from 14% to over 16%, which are the highest efficiencies for BDF copolymer-based organic solar cells.

Abstract

Molecular design of polymer donors is of vital importance for obtaining high-performance organic solar cells (OSCs). At present, much of the important progress in power conversion efficiencies (PCEs) achieved for OSCs has been associated with the benzodithiophene (BDT)-based polymers, while the highest PCE of benzo[1,2-b:4,5-b′]difuran (BDF) polymer-based OSCs only reaches 14.0%. Here, a polymer donor named PBDF-NS is designed and synthesized by using naphthalene-substituted benzo[1,2-b:4,5-b′]difuran as the electron-sufficient units and fluorinated benzotriazole (BTz) as the electron-deficient units. PBDF-NS possesses a low-lying HOMO level of −5.44 eV and a wide bandgap of 1.87 eV. When using LC301 as the acceptor, PBDF-NS-based OSC exhibits an excellent PCE of 15.24%. Moreover, the ternary and all-polymer devices based on PBDF-NS both achieve a higher PCE over 16%, which represents the highest efficiency values reported for BDF polymer-based OSCs in the literature thus far. Meanwhile, the binary and ternary devices all display excellent storage and light-soaking stabilities. The results demonstrate that by rational molecular design, BDF-based copolymers can be comparable to or even surpass the performance of BDT-based counterparts and also show great potential for realizing high-efficiency all-polymer solar cells.

The possibilities of different deposition techniques which can bring quantum dot (QD)-based solar cells to the industrial level are assessed. With perovskite QDs showing dramatic improvements in photovoltaics, the discussions on the challenges particularly for perovskite QD solar cells are given in an attempt to achieve large-area fabrication solving pivotal energy and environmental issues.

Abstract

Colloidally grown nanosized semiconductors yield extremely high-quality optoelectronic materials. Many examples have pointed to near perfect photoluminescence quantum yields, allowing for technology-leading materials such as high purity color centers in display technology. Furthermore, because of high chemical yield, and improved understanding of the surfaces, these materials, particularly colloidal quantum dots (QDs) can also be ideal candidates for other optoelectronic applications. Given the urgent necessity toward carbon neutrality, electricity from solar photovoltaics will play a large role in the power generation sector. QDs are developed and shown dramatic improvements over the past 15 years as photoactive materials in photovoltaics with various innovative deposition properties which can lead to exceptionally low-cost and high-performance devices. Once the key issues related to charge transport in optically thick arrays are addressed, QD-based photovoltaic technology can become a better candidate for practical application. In this article, the authors show how the possibilities of different deposition techniques can bring QD-based solar cells to the industrial level and discuss the challenges for perovskite QD solar cells in particular, to achieve large-area fabrication for further advancing technology to solve pivotal energy and environmental issues.

Publication date: April 2022

Source: Nano Energy, Volume 94

Author(s): Sanwan Liu, Rui Chen, Xueying Tian, Zhichun Yang, Jing Zhou, Fumeng Ren, Shasha Zhang, Yiqiang Zhang, Mengfan Guo, Yang Shen, Zonghao Liu, Wei Chen