Highly Efficient Porphyrin‐Based OPV/Perovskite Hybrid Solar Cells with Extended Photoresponse and High Fill Factor

Employing a layer of bulk‐heterojunction (BHJ) organic semiconductors on top of perovskite to further extend its photoresponse is considered as a simple and promising way to enhance the efficiency of perovskite‐based solar cells, instead of using tandem devices or near infrared (NIR)‐absorbing Sn‐containing perovskites. However, the progress made from this approach is quite limited because very few such hybrid solar cells can simultaneously show high short‐circuit current (J_SC) and fill factor (FF). To find an appropriate NIR‐absorbing BHJ is essential for highly efficient, organic, photovoltaics (OPV)/perovskite hybrid solar cells. The materials involved in the BHJ layer not only need to have broad photoresponse to increase J_SC, but also possess suitable energy levels and high mobility to afford high V_OC and FF. In this work, a new porphyrin is synthesized and blended with [6,6]‐phenyl‐C61‐butyric acid methyl ester (PCBM) to function as an efficient BHJ for OPV/perovskite hybrid solar cells. The extended photoresponse, well‐matched energy levels, and high hole mobility from optimized BHJ morphology afford a very high power conversion efficiency (PCE) (19.02%) with high V_oc, J_SC, and FF achieved simultaneously. This is the highest value reported so far for such hybrid devices, which demonstrates the feasibility of further improving the efficiency of perovskite devices.     

MoO3 buffer layer effect on photovoltaic properties of interpenetrating heterojunction type organic solar cells

Photovoltaic cells, with a conducting polymer/fullerene (C₆₀) interpenetrating heterojunction structure fabricated by spin-coating a conducting polymer onto a C₆₀ thin film, have been investigated and demonstrated a high efficiency as solar cells based on organic materials. The photovoltaic properties of the solar cells with a structure of indium-tin-oxide (ITO)/C₆₀/poly(3-hexylthiophene) (PAT6)/Au have been improved by the insertion of a molybdenum trioxide (VI) (MoO₃) layer as a cathode buffer layer. In the solar cells with the structure of ITO/C₆₀/PAT6/MoO₃/Au, the energy conversion efficiency has been improved to 1.15% under AM1.5 (100 mW/cm²) illumination.     

Simplified Perovskite Solar Cell with 4.1% Efficiency Employing Inorganic CsPbBr3 as Light Absorber

Perovskite solar cells with cost‐effectiveness, high power conversion efficiency, and improved stability are promising solutions to the energy crisis and environmental pollution. However, a wide‐bandgap inorganic–semiconductor electron‐transporting layer such as TiO₂ can harvest ultraviolet light to photodegrade perovskite halides, and the high cost of a state‐of‐the‐art hole‐transporting layer is an economic burden for commercialization. Here, the building of a simplified cesium lead bromide (CsPbBr₃) perovskite solar cell with fluorine‐doped tin oxide (FTO)/CsPbBr₃/carbon architecture by a multistep solution‐processed deposition technology is demonstrated, achieving an efficiency as high as 4.1% and improved stability upon interfacial modification by graphene quantum dots and CsPbBrI₂ quantum dots. This work provides new opportunities of building next‐generation solar cells with significantly simplified processes and reduced production costs.     

Interfacial Molecular Doping of Metal Halide Perovskites for Highly Efficient Solar Cells

Tailoring the doping of semiconductors in heterojunction solar cells shows tremendous success in enhancing the performance of many types of inorganic solar cells, while it is found challenging in perovskite solar cells because of the difficulty in doping perovskites in a controllable way. Here, a small molecule of 4,4′,4″,4″′-(pyrazine-2,3,5,6-tetrayl) tetrakis (N,N-bis(4-methoxyphenyl) aniline) (PT-TPA) which can effectively p-dope the surface of FA_xMA_1−xPbI₃ (FA: HC(NH₂)₂; MA: CH₃NH₃) perovskite films is reported. The intermolecular charge transfer property of PT-TPA forms a stabilized resonance structure to accept electrons from perovskites. The doping effect increases perovskite dark conductivity and carrier concentration by up to 4737 times. Computation shows that electrons in the first two layers of octahedral cages in perovskites are transferred to PT-TPA. After applying PT-TPA into perovskite solar cells, the doping-induced band bending in perovskite effectively facilitates hole extraction to hole transport layer and expels electrons toward cathode side, which reduces the charge recombination there. The optimized devices demonstrate an increased photovoltage from 1.12 to 1.17 V and an efficiency of 23.4% from photocurrent scanning with a stabilized efficiency of 22.9%. The findings demonstrate that molecular doping is an effective route to control the interfacial charge recombination in perovskite solar cells which is in complimentary to broadly applied defect passivation techniques.     

Developing 1D Sb‐Embedded Carbon Nanorods to Improve Efficiency and Stability of Inverted Planar Perovskite Solar Cells

To overcome the zigzag pathway transport of the electron diffusion process and eliminate the surface trap states of phenyl‐C61‐butyric acid methyl ester (PCBM) nanofilms in inverted perovskite solar cells, novel 1D N‐type doped carbon nanorods (CNRs) are developed by a stibonium (Sb) auxiliary ball milling method and introduced into the PCBM film to prepare the PCBM:Sb‐CNRs hybrid transport layer. In this way, the N‐type doped Sb‐CNRs can extend the built‐in electric field between CH₃NH₃PbI₃ and PCBM to facilitate the separation of electron/hole pairs. The discontinuous band with the built‐in potential in the PCBM/Sb‐CNRs heterojunction can boost interfacial charge redistribution and promote electrons diffusion from PCBM to electrode through 1D Sb‐CNRs network. As a result, the high device efficiency of 19.26% with enhanced air stability and little hysteresis are achieved. This work demonstrates a simple strategy to improve the efficiency and stability of perovskite photovoltaic devices using low‐cost carbon nanomaterials.     

TiO2 Electron Transport Bilayer for Highly Efficient Planar Perovskite Solar Cell

In planar perovskite solar cells, it is vital to engineer the extraction and recombination of electron–hole pairs at the electron transport layer/perovskite interface for obtaining high performance. This study reports a novel titanium oxide (TiO₂) bilayer with different Fermi energy levels by combing atomic layer deposition and spin‐coating technique. Energy band alignments of TiO₂ bilayer can be modulated by controlling the deposition order of layers. The TiO₂ bilayer based perovskite solar cells are highly efficient in carrier extraction, recombination suppression, and defect passivation, and thus demonstrate champion efficiencies up to 16.5%, presenting almost 50% enhancement compared to the TiO₂ single layer based counterparts. The results suggest that the bilayer with type II band alignment as electron transport layers provides an efficient approach for constructing high‐performance planar perovskite solar cells.     

Enhancing the Performance of Perovskite Solar Cells by Hybridizing SnS Quantum Dots with CH3NH3PbI3

The combination of perovskite solar cells and quantum dot solar cells has significant potential due to the complementary nature of the two constituent materials. In this study, solar cells (SCs) with a hybrid CH₃NH₃PbI₃/SnS quantum dots (QDs) absorber layer are fabricated by a facile and universal in situ crystallization method, enabling easy embedding of the QDs in perovskite layer. Compared with SCs based on CH₃NH₃PbI₃, SCs using CH₃NH₃PbI₃/SnS QDs hybrid films as absorber achieves a 25% enhancement in efficiency, giving rise to an efficiency of 16.8%. The performance improvement can be attributed to the improved crystallinity of the absorber, enhanced photo‐induced carriers' separation and transport within the absorber layer, and improved incident light utilization. The generality of the methods used in this work paves a universal pathway for preparing other perovskite/QDs hybrid materials and the synthesis of entire nontoxic perovskite/QDs hybrid structure.     

Multichannel Interdiffusion Driven FASnI3 Film Formation Using Aqueous Hybrid Salt/Polymer Solutions toward Flexible Lead‐Free Perovskite Solar Cells

Tin (Sn)‐based perovskites are increasingly attractive because they offer lead‐free alternatives in perovskite solar cells. However, depositing high‐quality Sn‐based perovskite films is still a challenge, particularly for low‐temperature planar heterojunction (PHJ) devices. Here, a “multichannel interdiffusion” protocol is demonstrated by annealing stacked layers of aqueous solution deposited formamidinium iodide (FAI)/polymer layer followed with an evaporated SnI₂ layer to create uniform FASnI₃ films. In this protocol, tiny FAI crystals, significantly inhibited by the introduced polymer, can offer multiple interdiffusion pathways for complete reaction with SnI₂. What is more, water, rather than traditional aprotic organic solvents, is used to dissolve the precursors. The best‐performing FASnI₃ PHJ solar cell assembled by this protocol exhibits a power conversion efficiency (PCE) of 3.98%. In addition, a flexible FASnI₃‐based flexible solar cell assembled on a polyethylene naphthalate–indium tin oxide flexible substrate with a PCE of 3.12% is demonstrated. This novel interdiffusion process can help to further boost the performance of lead‐free Sn‐based perovskites.     

Highly Efficient and Stable Flexible Perovskite Solar Cells with Metal Oxides Nanoparticle Charge Extraction Layers

In this study, the fabrication of highly efficient and durable flexible inverted perovskite solar cells (PSCs) is reported. Presynthesized, solution‐derived NiO_x and ZnO nanoparticles films are employed at room temperature as a hole transport layer (HTL) and electron transport layer (ETL), respectively. The triple cation perovskite films are produced in a single step and for the sake of comparison, ultrasmooth and pinhole‐free absorbing layers are also fabricated using MAPbI₃ perovskite. The triple cation perovskite cells exhibit champion power conversion efficiencies (PCEs) of 18.6% with high stabilized power conversion efficiency of 17.7% on rigid glass/indium tin oxide (ITO) substrates (comparing with 16.6% PCE with 16.1% stabilized output efficiency for the flexible polyethylene naphthalate (PEN)/thin film barrier/ITO substrates). More interestingly, the durability of flexible PSC under simulation of operative condition is proved. Over 85% of the maximum stabilized output efficiency is retained after 1000 h aging employing a thin MAPbI₃ perovskite (over 90% after 500 h with a thick triple cation perovskite). This result is comparable to a similar state of the art rigid PSC and represents a breakthrough in the stability of flexible PSC using ETLs and HTLs compatible with roll to roll production speed, thanks to their room temperature processing.     

Reducing Hysteresis and Enhancing Performance of Perovskite Solar Cells Using Low‐Temperature Processed Y‐Doped SnO2 Nanosheets as Electron Selective Layers

Despite the rapid increase of efficiency, perovskite solar cells (PSCs) still face some challenges, one of which is the current–voltage hysteresis. Herein, it is reported that yttrium‐doped tin dioxide (Y‐SnO₂) electron selective layer (ESL) synthesized by an in situ hydrothermal growth process at 95 °C can significantly reduce the hysteresis and improve the performance of PSCs. Comparison studies reveal two main effects of Y doping of SnO₂ ESLs: (1) it promotes the formation of well‐aligned and more homogeneous distribution of SnO₂ nanosheet arrays (NSAs), which allows better perovskite infiltration, better contacts of perovskite with SnO₂ nanosheets, and improves electron transfer from perovskite to ESL; (2) it enlarges the band gap and upshifts the band energy levels, resulting in better energy level alignment with perovskite and reduced charge recombination at NSA/perovskite interfaces. As a result, PSCs using Y‐SnO₂ NSA ESLs exhibit much less hysteresis and better performance compared with the cells using pristine SnO₂ NSA ESLs. The champion cell using Y‐SnO₂ NSA ESL achieves a photovoltaic conversion efficiency of 17.29% (16.97%) when measured under reverse (forward) voltage scanning and a steady‐state efficiency of 16.25%. The results suggest that low‐temperature hydrothermal‐synthesized Y‐SnO₂ NSA is a promising ESL for fabricating efficient and hysteresis‐less PSC.     

Highly Reproducible Large‐Area Perovskite Solar Cell Fabrication via Continuous Megasonic Spray Coating of CH3NH3PbI3

A simple, low‐cost, large area, and continuous scalable coating method is proposed for the fabrication of hybrid organic–inorganic perovskite solar cells. A megasonic spray‐coating method utilizing a 1.7 MHz megasonic nebulizer that could fabricate reproducible large‐area planar efficient perovskite films is developed. The coating method fabricates uniform large‐area perovskite film with large‐sized grain since smaller and narrower sized mist droplets than those generated by existing ultrasonic spray methods could be generated by megasonic spraying. The volume flow rate of the CH₃NH₃PbI₃ precursor solution and the reaction temperature are controlled, to obtain a high quality perovskite active layer. The devices reach a maximum efficiency of 16.9%, with an average efficiency of 16.4% from 21 samples. The applicability of megasonic spray coating to the fabrication of large‐area solar cells (1 cm²), with a power conversion efficiency of 14.2%, is also demonstrated. This is a record high efficiency for large‐area perovskite solar cells fabricated by continuous spray coating.     

Highly Efficient Planar Perovskite Solar Cells Via Interfacial Modification with Fullerene Derivatives

Planar heterojunction perovskite solar cells with a high efficiency up to 17.76% are fabricated by modifying the compact TiO₂ (c‐TiO₂) with a [6,6]‐phenyl‐C₆₁‐butyric acid (PCBA) monolayer. High quality CH₃NH₃PbI₃ films can be easily fabricated on PCBA‐modified c‐TiO₂ substrates by a one‐step solution processing method. Significant improvements of the device parameters are observed after PCBA modification. A high open‐circuit voltage (V_oc) of 1.16 V has been achieved, indicating that the PCBA monolayer can act as a hole blocking layer to reduce the trap site density atop the c‐TiO₂ and the hole recombination at the c‐TiO₂/perovskite interface. The enhancement of the fill factor, as well as the partial quenching of the fluorescence of perovskite after modification with PCBA, reveals that the charge extraction is improved.     

Mixed Valence Perovskite Cs2Au2I6: A Potential Material for Thin‐Film Pb‐Free Photovoltaic Cells with Ultrahigh Efficiency

New light is shed on the previously known perovskite material, Cs₂Au₂I₆, as a potential active material for high‐efficiency thin‐film Pb‐free photovoltaic cells. First‐principles calculations demonstrate that Cs₂Au₂I₆ has an optimal band gap that is close to the Shockley–Queisser value. The band gap size is governed by intermediate band formation. Charge disproportionation on Au makes Cs₂Au₂I₆ a double‐perovskite material, although it is stoichiometrically a single perovskite. In contrast to most previously discussed double perovskites, Cs₂Au₂I₆ has a direct‐band‐gap feature, and optical simulation predicts that a very thin layer of active material is sufficient to achieve a high photoconversion efficiency using a polycrystalline film layer. The already confirmed synthesizability of this material, coupled with the state‐of‐the‐art multiscale simulations connecting from the material to the device, strongly suggests that Cs₂Au₂I₆ will serve as the active material in highly efficient, nontoxic, and thin‐film perovskite solar cells in the very near future.     

CuGaSe2 solar cells using atomic layer deposited Zn(O,S) and (Zn,Mg)O buffer layers

The band gap of Zn(O,S) and (Zn,Mg)O buffer layers are varied with the objective of changing the conduction band alignment at the buffer layer/CuGaSe₂ interface. To achieve this, alternative buffer layers are deposited using atomic layer deposition. The optimal compositions for CuGaSe₂ solar cells are found to be close to the same for (Zn,Mg)O and the same for Zn(O,S) as in the CuIn_0.7Ga_0.3Se₂ solar cell case. At the optimal compositions the solar cell conversion efficiency for (Zn,Mg)O buffer layers is 6.2% and for Zn(O,S) buffer layers it is 3.9% compared to the CdS reference cells which have 5-8% efficiency.     

Enhancement of the power conversion efficiency of polymer solar cells by functionalized single-walled carbon nanotubes decorated with CdSe/ZnS core–shell colloidal quantum dots

In this paper, we demonstrated an enhanced performance of polymer solar cells by incorporating functionalized single-walled carbon nanotubes (SWCNTs) decorated with CdSe/ZnS core–shell colloidal quantum dots (CQDs) into copolymers of poly(3-hexylthiophene) (P3HT) and [6,6]-phenyl-C₆₁-butyric acid methyl ester (PCBM) as active layer. Short-circuit current density and power conversion efficiency of the ITO/PEDOT:PSS/P3HT:PCBM:(CdSe/ZnS-SWCNTs)/Al solar cells can be enhanced by more than 31 and 23 %, respectively, as compared with the control device ITO/PEDOT:PSS/P3HT:PCBM/Al. This enhancement is due to the high electron-transporting ability of SWCNTs and the increased absorption of CdSe/ZnS CQD in visible region. It shows an applicable way to improve the efficiency of polymer solar cells by incorporating suitable quantity of CQDs-decorated SWCNTs with suitable kinds of CQDs and suitable acid treatment to the SWCNTs.     

Bridging the Buried Interface with Piperazine Dihydriodide Layer for High Performance Inverted Solar Cells

Given that it is closely related to perovskite crystallization and interfacial trap densities, buried interfacial engineering is crucial for creating effective and stable perovskite solar cells. Compared with the in-depth studies on the defect at the top perovskite interface, exploring the defect of the buried side of perovskite film is relatively complicated and scanty owing to the non-exposed feature. Herein, the degradation process is probed from the buried side of perovskite films with continuous illumination and its effects on morphology and photoelectronic characteristics with a facile lift-off method. Additionally, a buffer layer of Piperazine Dihydriodide (PDI₂) is inserted into the imbedded bottom interface. The PDI₂ buffer layer is able to lubricate the mismatched thermal expansion between perovskite and substrate, resulting in the release of lattice strain and thus a void-free buried interface. With the PDI₂ buffer layer, the degradation originates from the growing voids and increasing non-radiative recombination at the imbedded bottom interfaces are suppressed effectively, leading to prolonged operation lifetime of the perovskite solar cells. As a result, the power conversion efficiency of an optimized p-i-n inverted photovoltaic device reaches 23.47% (with certified 23.42%) and the unencapsulated devices maintain 90.27% of initial efficiency after 800 h continuous light soaking.     

A Biopolymer Heparin Sodium Interlayer Anchoring TiO2 and MAPbI3 Enhances Trap Passivation and Device Stability in Perovskite Solar Cells

Traps in the photoactive layer or interface can critically influence photovoltaic device characteristics and stabilities. Here, traps passivation and retardation on device degradation for methylammonium lead trihalide (MAPbI₃) perovskite solar cells enabled by a biopolymer heparin sodium (HS) interfacial layer is investigated. The incorporated HS boosts the power conversion efficiency from 17.2 to 20.1% with suppressed hysteresis and Shockley–Read–Hall recombination, which originates primarily from the passivation of traps near the interface between the perovskites and the TiO₂ cathode. The incorporation of an HS interfacial layer also leads to a considerable retardation of device degradation, by which 85% of the initial performance is maintained after 70 d storage in ambient environment. Aided by density functional theory calculations, it is found that the passivation of MAPbI₃ and TiO₂ surfaces by HS occurs through the interactions of the functional groups (? COO^?, ? SO₃^?, or Na⁺) in HS with undersaturated Pb and I ions in MAPbI₃ and Ti⁴⁺ in TiO₂. This work demonstrates a highly viable and facile interface strategy using biomaterials to afford high‐performance and stable perovskite solar cells.     

Solution‐Phase Epitaxial Growth of Perovskite Films on 2D Material Flakes for High‐Performance Solar Cells

The quality of perovskite films is critical to the performance of perovskite solar cells. However, it is challenging to control the crystallinity and orientation of solution‐processed perovskite films. Here, solution‐phase van der Waals epitaxy growth of MAPbI₃ perovskite films on MoS₂ flakes is reported. Under transmission electron microscopy, in‐plane coupling between the perovskite and the MoS₂ crystal lattices is observed, leading to perovskite films with larger grain size, lower trap density, and preferential growth orientation along (110) normal to the MoS₂ surface. In perovskite solar cells, when perovskite active layers are grown on MoS₂ flakes coated on hole‐transport layers, the power conversion efficiency is substantially enhanced for 15%, relatively, due to the increased crystallinity of the perovskite layer and the improved hole extraction and transfer rate at the interface. This work paves a way for preparing high‐performance perovskite solar cells and other optoelectronic devices by introducing 2D materials as interfacial layers.     

Realizing Stable Artificial Photon Energy Harvesting Based on Perovskite Solar Cells for Diverse Applications

As the fastest developing photovoltaic device, perovskite solar cells have achieved an extraordinary power conversion efficiency (PCE) of 25.3% under AM 1.5 illumination. However, few studies have been devoted to perovskite solar cells harvesting artificial light, owing to the great challenge in the simultaneous manipulation of bandgap‐adjustable perovskite materials, corresponding matched energy band structure of carrier transport materials, and interfacial defects. Herein, through systematic morphology, composition, and energy band engineering, high‐quality Cs_0.05MA_0.95PbBr_xI_3?x perovskite as the light absorber and Nb_yTi_1?yO₂ (Nb:TiO₂) as the electron transport material with an ideal energy band alignment are obtained simultaneously. The theoretical‐limit‐approaching record PCEs of 36.3% (average: 34.0 ± 1.2%) under light‐emitting diode (LED, warm white) and 33.2% under fluorescent lamp (cold white) are achieved simultaneously, as well as a PCE of 19.5% (average: 18.9 ± 0.3%) under solar illumination. An integrated energy conversion and storage system based on an artificial light response solar cell and sodium‐ion battery is established for diverse practical applications, including a portable calculator, quartz clock, and even environmental monitoring equipment. Over a week of stable operation shows its great practical potential and provides a new avenue to promote the commercialization of perovskite photovoltaic devices via integration with ingenious electronic devices.     

Reduced Interface‐Mediated Recombination for High Open‐Circuit Voltages in CH3NH3PbI3 Solar Cells

Perovskite solar cells with all‐organic transport layers exhibit efficiencies rivaling their counterparts that employ inorganic transport layers, while avoiding high‐temperature processing. Herein, it is investigated how the choice of the fullerene derivative employed in the electron‐transporting layer of inverted perovskite cells affects the open‐circuit voltage (V_OC). It is shown that nonradiative recombination mediated by the electron‐transporting layer is the limiting factor for the V_OC in the cells. By inserting an ultrathin layer of an insulating polymer between the active CH₃NH₃PbI₃ perovskite and the fullerene, an external radiative efficiency of up to 0.3%, a V_OC as high as 1.16 V, and a power conversion efficiency of 19.4% are realized. The results show that the reduction of nonradiative recombination due to charge‐blocking at the perovskite/organic interface is more important than proper level alignment in the search for ideal selective contacts toward high V_OC and efficiency.