Efficient All-inorganic Perovskite Solar Cells Research Articles

Multifunctional molecular bridge enabled interface passivation and strain release for stable and efficient all-inorganic perovskite solar cells

The precise management of the buried interface in n-i-p perovskite solar cells (PSCs) to achieve efficient charge extraction and transport is crucial for improving the photovoltaic performance. Here, a 4-chloro-2,5-dimethoxyaniline (CDA) modifier with multifunctional groups is utilized as a molecular bridge at the TiO2/CsPbBr3 buried interface to enhance the qualities of TiO2 and CsPbBr3 films and the arrangement of interface energy level. The chlorine atom in CDA can heal the oxygen vacancies defects on the TiO2 film surface, thereby improving its electron mobility and conductivity. The –O– and –NH2 groups in CDA play a passivation effect on the ions defects of CsPbBr3 film, and especially the two –O– groups can anchor the lattice Pb atoms of CsPbBr3 perovskite, which effectively reduce the trap states of CsPbBr3 film and release the residual lattice strain. The modification of CDA also improves the wettability and energy level of TiO2 film to optimize CsPbBr3 crystal growth and charge transport, respectively. Consequently, the CsPbBr3 PSCs with CDA molecular bridge free of encapsulation achieve a highly increased power conversion efficiency of 10.85 %, in contrast with 8.16 % value of the control device. After 720 h of storage at 85 °C and in air environment with 85 % relative humidity, the efficiency of the CDA-modified device retains 93.1 % of the initial value, demonstrating excellent long-term humidity and thermal stability.

Screening of Functional Small Molecules via Modified Machine Learning Strategy toward Efficient All-Inorganic Perovskite Solar Cells.

Organic small molecules are proven to be capable of passivating the bulk/interfacial defects in inorganic perovskite solar cells. Considering the burdensome situation to screen the functional small molecules, we employ a modified machine learning (ML) strategy to guide screening suitable small molecules toward efficient solar cells through three modified ML algorithms to construct the prediction model: (i) random forest algorithm (RF), (ii) support vector machine algorithm (SVR), and (iii) XGBoost. Among them, the XGBoost algorithm displays a better overall predictive performance, whereby the R2 index reaches 0.939. Accordingly, eight small molecules are selected to modify the interface of perovskite films, and both the theoretical and experimental results certify that the difluorobenzylamine with additional fluorine atoms has a better interface modification effect among the small molecules containing functional groups, e.g., the benzene ring and amino group. The high accuracy of the modified machine learning model enables us to simplify the small-molecule screening process and form an important step for ongoing developments in perovskite solar cells and other optoelectronic devices.

Doping with KBr to Achieve High-Performance CsPbBr3 Semitransparent Perovskite Solar Cells.

Wide-bandgap semitransparent perovskite photovoltaics are emerging as one of the ideal candidates for building-integrated photovoltaics (BIPV). However, surface defects in inorganic CsPbBr3 perovskite prepared by vapor deposition severely limit the optoelectronic performance of perovskite solar cells. To address this issue, a strategy of doping a trace amount of KBr into perovskite by vapor deposition is adopted, effectively improving the quality of the film, reducing surface defect concentration, and enhancing the transportation and extraction of charge carriers. Simultaneously, fully physical vapor deposition technology is employed to fabricate perovskite solar cells with an average visible light transmittance of 44%. These devices exhibited an ultrahigh open-circuit voltage of 1.55 V and a superior power conversion efficiency (PCE) of 7.28%, demonstrating excellent moisture and heat resistance. Moreover, the corresponding 5 cm × 5 cm modules achieve a PCE of 5.35% with great thermal insulation capability. This work provides an approach for fabricating highly efficient all-inorganic perovskite solar cells with high average visible light transmittance, demonstrating new insights into their application in building-integrated photovoltaics.

A Mixed Antisolvent-Assisted Crystallization Strategy for Efficient All-Inorganic CsPbIBr2 Perovskite Solar Cells by a Low-Temperature Process

To improve the microstructure of low-temperature-processed CsPbIBr2 films, a chlorobenzene (CB) and isopropyl alcohol (IPA) mixed solution is used as an antisolvent to fabricate CsPbIBr2 films. It is found that the modified film by the mixed antisolvent demonstrates a better morphology, crystallinity, absorption of sunlight, less trap-state density (Ntrap), and suppressed carrier recombination. The modified perovskite solar cells (PSCs) without a hole-transport layer (HTL) achieve a champion efficiency of 7.05%, being much higher by 28.18% than that of the Reference-PSCs without an antisolvent. Moreover, the HTL of undoped zinc phthalocyanine (ZnPc) prepared by solution processing is used to promote charge transfer and protect the CsPbIBr2 film from damage caused by humid air at the CsPbIBr2/carbon interface. The best PSC with a structure of FTO/TiO2/CsPbIBr2/ZnPc/carbon yields a champion efficiency of 8.48% (Reference-PSC, 5.50%) with an open-circuit voltage of 1.23 V. The modified PSCs without encapsulation demonstrate improved humidity stability and retain about 90% (Reference-PSC, ∼70%) of their initial efficiency after storage at a 20% relative humidity in air for 30 days. In addition, the modified PSCs possess good light and thermal stability. Our work provides a feasible low-temperature (150 °C) process to prepare CsPbIBr2 films with the preferred orientation and stable, efficient all-inorganic PSCs (200 °C).

Understanding steric-charge-dependence of conjugated passivators on π-Pb2+ bond strength for efficient all-inorganic perovskite solar cells

Intramolecular structure of interfacial passivator highly determines the bond strength with detrimental defects located at perovskite surfaces and grain boundaries. Herein, we investigate the steric-charge-dependence of various π-conjugated pyridine derivatives on electron-donating ability to passivate inorganic CsPbIBr2 perovskite film. The primary results demonstrate that the photovoltaic performances tightly correlate with the multidentate coordination sites and structure-steric hindrance because of their synergistic regulation on intramolecular electron-cloudy density and charge extraction. Comparing to pyridine and terpyridine treated devices, the bipyridine passivated device delivers an increased efficiency of 11.04% with a high open-circuit voltage of 1.301 V and improved stability after persistent irradiation over 20 h and storage for 60 days, which is one of the highest efficiencies for carbon-based all-inorganic CsPbIBr2 solar cells. This work provides a direction to choose ideal passivator for high-efficiency perovskite optoelectronics.

A green Bi-Solvent system for processing high-quality CsPbBr3 films in efficient all-inorganic perovskite solar cells

All-brominated inorganic perovskite CsPbBr3 has received much attention in the field of optoelectronic applications owing to its superb stability and ease of manufacture under the ambient condition. However, the tedious process and toxic solvent are two major challenges for fabrication of CsPbBr3 films via a multi-step deposition method. Here, we demonstrate a sustainable bi-solvent system for preparing high-quality CsPbBr3 films in a triple-step solution-processed route, where the bi-solvent system comprises of green solvent water and ethylene glycol monomethyl ether (EGME) in place of the noxious methanol for CsBr solution. By adjusting the temperature of heat treatment and spin-coating speed, the pinhole-free, ultra-smooth and high crystallinity of CsPbBr3 films were obtained. As a result, the CsPbBr3 PSC prepared from the green bi-solvent system demonstrates an optimal power conversion efficiency (PCE) of 9.55%, which is one of the highest efficiencies for planar carbon-based PSCs without hole transport layer. Moreover, the all-inorganic unpacked PSCs exhibit excellent humidity stability under ambient environment for 34 days. Our result not only offers a facile and simple way to fabricate the pure-phase CsPbBr3 films, but also alleviates the solvent toxicity during the preparation of CsPbBr3 PSCs.

Constructing highly efficient all-inorganic perovskite solar cells with efficiency exceeding 17% by using dopant-free polymeric electron-donor materials

Abstract Development of all-inorganic perovskite solar cells (PSCs) is highly desirable due to its excellent thermal stability and great potential for tandem solar cells. One main bottleneck that restricts its further development is the absence of the ideal hole-transporting materials which is critical to device performance and stability. Herein, we construct a brand-new architecture of all-inorganic PSCs via employing a series of doping-free polymeric organic photovoltaic donor materials as hole transport materials including J71, PBDB-T, PM6 with suitable energy level and carrier transport ability. The mechanism in terms of film molecular microscopic structure, electrical transport dynamics, electrical potential distribution were systematically investigated by grazing incidence wide-angle X-ray scattering (GIWAXS), conductive atomic force microscope (C-AFM) and kelvin probe force microscopy (KPFM) measurements. This work not only proposes a series of new dopant-free polymeric hole transporting materials for all-inorganic PSCs, but also demonstrates the fabrication of high efficiency devices with power conversion efficiencies over 17%, a record of all-inorganic PSCs based on dopant-free polymeric materials to our knowledge.

Efficient All-Inorganic CsPbBr3 Perovskite Solar Cells by Using CdS/CdSe/CdS Quantum Dots as Intermediate Layers

Highly efficient all-inorganic perovskite solar cells require a fast charge transfer from CsPbBr3 to TiO2 to reduce the recombination from trap states. Herein, we insert a CdS/CdSe/CdS quantum dot (QD) layer between the TiO2 and CsPbBr3 layers to fabricate all-inorganic perovskite solar cells. By tuning the thicknesses of the CdSe layer of CdS/CdSe/CdS QDs, the conduction band (CB) levels can be adjusted to -3.72~-3.87 eV. After inserting the QD intermediate layer, the energy offset between the CB of TiO2 and CsPbBr3 is reduced, thus leading to a charge transfer rate boost from 0.040×109 to 0.059×109 s−1. The power conversion efficiency (PCE) of the solar cell with QD intermediate layer achieves 8.64%, which is 20% higher than its counterpart without QDs.

Highly efficient all-inorganic perovskite solar cells with suppressed non-radiative recombination by a Lewis base

All-inorganic perovskite solar cells (PVSCs) have drawn increasing attention because of their outstanding thermal stability. However, their performance is still inferior than the typical organic-inorganic counterparts, especially for the devices with p-i-n configuration. Herein, we successfully employ a Lewis base small molecule to passivate the inorganic perovskite film, and its derived PVSCs achieved a champion efficiency of 16.1% and a certificated efficiency of 15.6% with improved photostability, representing the most efficient inverted all-inorganic PVSCs to date. Our studies reveal that the nitrile (C-N) groups on the small molecule effectively reduce the trap density of the perovskite film and thus significantly suppresses the non-radiative recombination in the derived PVSC by passivating the Pb-exposed surface, resulting in an improved open-circuit voltage from 1.10 V to 1.16 V after passivation. This work provides an insight in the design of functional interlayers for improving efficiencies and stability of all-inorganic PVSCs.

Structured crystallization for efficient all-inorganic perovskite solar cells with high phase stability

Yttrium incorporation enhanced the performance of CsPbI2Br perovskite solar cells and the phase stability was improved significantly.

One-step solution deposition of CsPbBr3based on precursor engineering for efficient all-inorganic perovskite solar cells

A novel strategy of adopting cesium acetate and methylammonium acetate increases the concentration of CsPbBr3precursor solution assisting one-step deposition.