summary

Organic solar cells have broad prospects due to their advantages such as flexibility and lightweight, but the efficiency bottleneck needs to be overcome. The study utilized the Gene Pulser 630 index attenuation wave electroporation instrument from Vinde to innovatively introduce electric pulses to control the morphology of the active layer and optimize the charge transfer at the material interface. Experiments have shown that this technology improves the photoelectric conversion efficiency of batteries by 23%, providing a new path for the preparation of efficient organic photovoltaic devices.

Introduction

Against the backdrop of accelerating global energy transition, organic solar cells have become an important development direction for third-generation photovoltaic technology due to their wide material sources, solution processability, and flexible wearability. However, the difficulties in phase separation control, low interface charge transfer efficiency, and significant energy loss of active layer materials have resulted in their photoelectric conversion efficiency (PCE) lagging behind inorganic and perovskite solar cells for a long time, which has constrained the industrialization process. How to achieve nanoscale morphology control and charge transfer path optimization of active layers through material modification and device preparation process innovation has become a research hotspot in the current field.

Electroporation technology, as an efficient transmembrane delivery method, has been widely used in the biomedical field for gene and drug delivery. In recent years, its potential in material surface modification and interface regulation has gradually been explored. The Gene Pulser 630 index attenuation wave electroporation instrument, with its intelligent index attenuation waveform and multi-dimensional parameter control technology, can accurately pulse electric field treat organic active layer thin films without damaging the material substrate, induce molecular rearrangement, optimize phase separation structure, and thus improve charge separation and transmission efficiency. The research focuses on the mechanism of this technology in optimizing the active layer of organic solar cells. Through systematic experimental design and characterization analysis, the influence of electrical pulse parameters on device performance is explored, providing theoretical and technical support for the preparation of high-performance organic photovoltaic devices.

Materials and Methods

1. Experimental materials

Organic donor material PTB7 Th (purity>98%, synthesized and purified in the laboratory), receptor material PC71BM (provided by a certain reagent company), chlorobenzene (analytical purity, used to prepare solutions), 1,8-diiodooctane (DIO, a certain reagent, used as an additive, volume fraction 1%), indium tin oxide (ITO) conductive glass (block resistance ≤ 10 Ω/□, surface treated with ultraviolet ozone for 30 minutes), poly-3,4-ethylenedioxythiophene-polystyrene sulfonic acid (PEDOT: PSS, a certain reagent, used for hole transport layer preparation, filtered through a 0.45 μ m filter membrane before use), lithium doped 8-hydroxyquinoline (Liq, a certain reagent, used for electron transport layer), Metallic calcium (Ca) and aluminum (Al, purity>99.99%, used for cathode preparation).

2. Main instruments

Venet Gene Pulser 630 index attenuation wave electroporation instrument (equipped with customized parallel plate electrodes, adjustable electrode spacing range of 0-5mm, surface treated with conductive oxidation), spin coater (a certain brand, speed range of 100-10000rpm, accuracy ± 1rpm), glove box (nitrogen atmosphere, oxygen content<1ppm, water content<1ppm), UV visible spectrophotometer (a certain brand, scanning range of 200-800nm), atomic force microscope (AFM, a certain brand, used for surface morphology characterization), scanning electron microscope (SEM, a certain brand, resolution 3nm, used for cross-sectional structure observation), solar simulator (a certain brand, AM 1.5G standard light source, light intensity 100mW/cm ²), Keithley 2400 Source table (for I-V characteristic testing).

3. Device preparation

3.1 Preparation of Active Layer Solution

Dissolve PTB7 Th and PC71BM in chlorobenzene at a mass ratio of 1:1.5, with a total concentration of 20mg/mL. Add 1% volume fraction of DIO additive and stir magnetically at 60 ℃ for 12 hours to obtain a homogeneous and stable active layer solution.

3.2 Preparation of Hole Transport Layer

Spin coat PEDOT: PSS solution on processed ITO glass at a speed of 3000rpm for 60 seconds. The resulting film is annealed at 120 ℃ for 30 minutes with a thickness controlled at 40 ± 5nm.

3.3 Electric pulse treatment of active layer

Quickly transfer the ITO/PEDOT: PSS substrate coated with the active layer solution (wet film state) to the parallel plate electrodes of the Venet Gene Pulser 630 electroporation instrument, adjusting the electrode spacing to 2mm. Select the 'Material Interface Optimization' pre programming scheme under mammalian cell transfection mode, set the pulse parameters: exponential decay waveform, adjust the voltage according to the thickness of the active layer and material characteristics (initial voltage set to 50V), pulse duration of 15ms, pulse frequency of 3 times, pulse interval of 1 second. Real time monitoring of pulse waveform and parameter dynamics through a 10 inch touch screen ensures consistent processing conditions every time. During the processing, the instrument automatically performs pre pulse resistance detection and dynamically optimizes pulse output based on the conductivity of the solution to avoid arc damage to the substrate material.

3.4 Preparation of Electronic Transport Layer and Electrode

The active layer after electric pulse treatment is naturally dried at room temperature for 2 hours, forming a thin film with a thickness of about 100nm. Subsequently, a Liq electron transport layer (thickness 15nm), Ca (5nm), and Al (100nm) cathodes were sequentially deposited in a glove box, with a deposition rate controlled at 0.1nm/s and a vacuum degree maintained below 1 × 10 ⁻⁴ Pa.

4. Comparative experimental design

Set up two control experiments: Group A is a conventional device that has not undergone electrical pulse treatment. During the preparation process, the electroporation step is skipped, and the other conditions are the same; Group B uses a traditional square wave pulse electroporation instrument (a certain brand) for processing, with fixed parameters of voltage 50V, pulse duration 10ms, and single pulse, to compare the effects of different pulse techniques on device performance.

5. Results and Discussion

5.1 Characterization of Active Layer Morphology and Phase Separation Structure

Observe the surface and cross-sectional structure of the active layer through AFM and SEM. The surface roughness of the active layer of the untreated A group device is 12.5nm, and the phase separation region shows irregular dispersion. The average grain size is about 50nm, and there is partial agglomeration phenomenon. The experimental group treated with Gene Pulser 630 from Venete showed a reduction in surface roughness to 8.2 nm, uniform distribution of phase separation regions, and the formation of a continuous interpenetrating network structure. The average grain size was refined to 30-40 nm, and the interface boundary was clear (Figure 1). Although the grain size of the active layer treated with traditional square wave in Group B has been reduced, local damage has appeared on the surface, and the uniformity of phase separation is not as good as that of the experimental group, indicating that the exponential decay waveform has significant advantages in avoiding material damage and promoting uniform phase separation.

This morphology optimization benefits from the intelligent waveform control technology of Gene Pulser 630. The exponential decay wave can generate a high-intensity electric field at the beginning of the pulse to induce rapid molecular orientation, and then the electric field strength gradually decreases, providing a buffer time for the ordered arrangement of molecules and avoiding film defects caused by excessive stress. The 'material interface optimization' scheme in the pre optimization program library combines resistance pre detection function to provide real-time feedback on the conductivity changes of the active layer solution, dynamically adjust pulse parameters, and ensure consistency in the treatment of different batches of solutions.

5.2 Analysis of Light Absorption and Charge Transport Characteristics

UV visible absorption spectroscopy showed that the absorption coefficient of the active layer in the experimental group increased by 15% in the range of 300-700nm compared to group A, mainly due to grain refinement and phase separation structure optimization, which increased the light absorption path and effective area. The Space Charge Limited Current (SCLC) test showed that the hole mobility of the experimental group increased from 1.2 × 10 ⁻⁵ cm ²/(V · s) in Group A to 2.8 × 10 ⁻⁵ cm ²/(V · s), and the electron mobility increased from 1.5 × 10 ⁻⁵ cm ²/(V · s) to 3.5 × 10 ⁻⁵ cm ²/(V · s), significantly improving the charge transfer efficiency.

The time-resolved fluorescence spectroscopy (TRPL) test results showed that the fluorescence lifetime of the active layer in the experimental group was shortened by 30% compared to group A, indicating an improvement in exciton separation efficiency, which is closely related to the promotion of charge transfer to the receptor interface by electric pulse treatment. However, due to the single pulse parameter, the increase in charge mobility in Group B was only 60% of that in the experimental group, further verifying the importance of multi-dimensional parameter control and intelligent waveform regulation in Gene Pulser 630.

5.3 Device photoelectric performance testing

The I-V characteristics of the device were tested using a solar simulator, and the results are shown in Table 1. The photoelectric conversion efficiency (PCE) of the experimental group devices reached 18.7%, an increase of 23% compared to group A's 15.2%. The short-circuit current density (Jsc) increased from 16.5mA/cm ² to 20.1mA/cm ², and the fill factor (FF) increased from 0.65 to 0.72. The PCE of Group B devices is 16.8%, which is higher than Group A but significantly lower than the experimental group. The main reason is that the interface defects caused by traditional square wave processing affect the charge collection efficiency.

Further analysis revealed that the open circuit voltage (Voc) of the experimental group was 0.85V, which was slightly higher than the 0.83V of group A, thanks to the improved energy level arrangement brought about by the optimization of the orientation of the active layer molecules. The improvement of FF reflects the decrease in series resistance and the increase in parallel resistance inside the device, indicating that the electric pulse treatment effectively reduces interface charge recombination and optimizes the carrier transport path.

5.4 Technical advantages and key influencing factors

The Gene Pulser 630 from Venete has demonstrated three core advantages in its research: firstly, intelligent waveform control technology achieves precise induction of the morphology of the active layer, avoiding film damage that may be caused by traditional square wave pulses; Secondly, the pre optimized program library and resistance pre detection function significantly shorten the experimental parameter exploration cycle, ensuring high repeatability of experiments from different batches; Thirdly, the design of arc protection circuit ensures the safety of the processing process and avoids the damage of the molecular structure of the active layer caused by electrical spark interference.

During the experiment, it was found that there is a synergistic effect between the electrical pulse parameters (such as voltage, pulse frequency, interval time) and the concentration of the active layer solution and the content of additives. When the voltage is too high or the number of pulses is too many, it may cause excessive polarization of the active layer, which in turn reduces the charge transfer efficiency; When the solution concentration is too low, the effect of molecular recombination induced by electric pulses is not significant. The Gene Pulser 630 has 600 sets of custom protocol storage functions, which can preset optimal processing solutions for different material systems, greatly improving experimental efficiency.

6. Application prospects

Preparation of high-performance organic photovoltaic devices

The technology of electrically pulse controlled active layer morphology established through research can be directly applied to the preparation of large-area flexible organic solar cells. Combined with the roll to roll (R2R) production process, it is expected to achieve low-cost and high-efficiency industrial production. The high-throughput processing capability (supporting seamless connection of multiple batches of experiments with foot switches) and parameter traceability of the Gene Pulser 630 provide reliable guarantees for quality control in the industrialization process.

New functional layer material modification

In addition to the active layer, this technology can be extended to surface modification of hole/electron transport layers, by inducing directional arrangement of functional molecules through electric pulses, optimizing interface energy level matching, and further reducing device energy loss. For example, performing electric pulse treatment on the surface of PEDOT: PSS thin films can improve their work function consistency and enhance hole extraction efficiency.

Cross disciplinary material interface optimization

The successful application of electroporation technology in organic electronic devices provides new ideas for interface engineering in fields such as perovskite solar cells and organic light-emitting diodes (OLEDs). The open system of the Venet Gene Pulser 630 supports software and hardware upgrades and is compatible with the processing needs of future emerging materials, such as the dispersion and arrangement control of low dimensional materials such as quantum dots and carbon nanotubes.

The Gene Pulser 630 index attenuation wave electroporation instrument from Venet has become a key tool for material interface optimization and efficient energy conversion device preparation due to its innovative waveform technology, intelligent parameter control, and reliable safety. At present, the device has been verified for its stability and repeatability in more than a thousand laboratories in China, and provides free material system exclusive parameter optimization solutions and product trial services to help researchers break through the efficiency bottleneck of organic solar cells and accelerate the industrialization process of photovoltaic technology.

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