Periodic Reporting for period 1 - QuBics (Understanding the Working Mechanisms of Quaternary Blend Organic Photovoltaics (OPVs))
Okres sprawozdawczy: 2023-09-01 do 2026-01-31
The European Union has implemented the ambitious and essential European Green Deal to establish Europe as the first climate-neutral continent by 2050. Achieving this goal demands significant efforts to expand renewable energy sources and position them closer to end users, most of whom reside in urban areas. Photovoltaic (PV) technology, which converts solar energy into electricity without environmental harm, plays a key role in this transition. This project focuses on enhancing future energy systems by advancing urban-integrated PV technology using cutting-edge organic semiconductors. It aims to tackle scientific and commercialization challenges in emerging PV technologies, such as organic and perovskite solar cells, which have the potential to create new markets for cost-effective, climate-neutral, and circular products. We also aim to translate this technology from lab-to-fab with the help of our industrial partners to entice stakeholders and investors to invest in this future technology to develop low-cost energy solutions.
We have identified several key scientific and commercialization challenges limiting the practical efficiency of organic and perovskite solar cells:
1. Power conversion efficiency (PCE) is restricted by significant voltage and current losses due to inefficient charge transport.
2. A fundamental trade-off exists between voltage and current in these PV technologies, but the underlying physics remains poorly understood.
3. Scaling up from lab-scale devices to large-area industrial modules is challenging due to high resistive losses and difficulties in producing high-quality light-absorbing active layer thin films.
Our objective is to overcome these challenges by primarily employing p-type semiconducting polymers like PM6, D18, D18-Cl, PTQ10, and JD40-BDD20, which are extensively used in organic photovoltaics (OPVs) due to their excellent conductivity and hydrophobic properties. My primary goal is to integrate these polymers at the interface between perovskite and hole-transporting materials to optimize energy level alignment and improve hole extraction efficiency. For this project, we have set a realistic target of achieving a power conversion efficiency (PCE) exceeding 26% in small-area devices and over 20% in large-area modules.
We have identified several key scientific and commercialization challenges limiting the practical efficiency of organic and perovskite solar cells:
1. Power conversion efficiency (PCE) is restricted by significant voltage and current losses due to inefficient charge transport.
2. A fundamental trade-off exists between voltage and current in these PV technologies, but the underlying physics remains poorly understood.
3. Scaling up from lab-scale devices to large-area industrial modules is challenging due to high resistive losses and difficulties in producing high-quality light-absorbing active layer thin films.
Our objective is to overcome these challenges by primarily employing p-type semiconducting polymers like PM6, D18, D18-Cl, PTQ10, and JD40-BDD20, which are extensively used in organic photovoltaics (OPVs) due to their excellent conductivity and hydrophobic properties. My primary goal is to integrate these polymers at the interface between perovskite and hole-transporting materials to optimize energy level alignment and improve hole extraction efficiency. For this project, we have set a realistic target of achieving a power conversion efficiency (PCE) exceeding 26% in small-area devices and over 20% in large-area modules.
Task 1: The polymer screening process has been conducted, and among all the tested polymers (PM6, D18, D18-Cl, PTQ10, and JD40-BDD20), D18-Cl emerged as the most suitable for our purpose based on the following observations:
1. GIWAXS analysis revealed that D18-Cl exhibits superior π-π stacking, facilitating the formation of a compact and dense thin film.
2. The HOMO of D18-Cl aligns well with the valence band maximum (VBM) of perovskite and the HOMO of home-grown hole-transporting layer (HTL), spiro-OMeTAD, resulting in improved charge extraction.
3. Steady-state photoluminescence (PL) and time-resolved photoluminescence (TRPL) measurements confirmed that D18-Cl enhances hole extraction efficiency.
Building on our OPV experience, we successfully incorporated D18-Cl on the perovskite surface to passivate interface trap states. While the one-step spin-coating process with antisolvent pipetting is widely used to control perovskite nucleation and crystallization, surface defects often lead to poor interfaces with charge-transport layers. To address this, we introduced D18-Cl into the antisolvent as a template agent, achieving high PCE even without additives in spiro-OMeTAD. This approach effectively modifies the perovskite/spiro-OMeTAD interface, enabling a simple and efficient antisolvent engineering technique.
Achievement 1: Using the anti-solvent film deposition method, we fabricated perovskite solar cells with the structure: ITO/SnO2/perovskite/OAI/spiro-OMeTAD/gold. After testing concentrations from 0.5 to 2.5 mg/ml, 1 mg/ml of D18-Cl was found optimal. The device performance (Figure 1) were compared for two antisolvent conditions: (1) pure CB (control) and (2) CB with 1 mg/ml D18-Cl. Both used identical HTL conditions without additives. Perovskite (D18-Cl)-based devices showed a 0.07 V increase in voltage, reducing recombination losses, and an fill factor rise from 75% to over 81%, improving charge extraction. This approach increased the efficiency from below 19% to over 23%.
Task 2: It is crucial to investigate the role of D18-Cl in the perovskite antisolvent. This includes performing various surface analyses, such as XRD, XPS, UPS, ToF-SIMS, FTIR, and SEM, alongside optical and electrical characterizations, to evaluate any changes in the perovskite's properties and surface. A key aspect of this work is determining whether the polymer remains on the perovskite surface or penetrates into its bulk. To explore this further, we also conducted X-ray reflectivity (XRR) and Neutron reflectivity (NR) measurements.
Achievement 2: From XRR and NR measurements (Figure 2), we identified an ultra-thin (1.2 nm) pure polymer layer on top and a 10 nm mixed region (D18-Cl and perovskite) underneath. These layers support proper energy level alignment and charge transport. UPS analysis (Figure 3) revealed that without the polymer, strong charge transfer (dipole size: 0.52 eV) occurs at the perovskite/spiro-OMeTAD interface, potentially leading to spiro-OMeTAD dedoping. With the polymer, weaker charge transfer (dipole size: 0.15 eV) occurs, reducing dedoping. The potential gradient in the D18-Cl layer promotes hole transport from the perovskite to the anode while blocking electrons, suggesting that D18-Cl acts as an efficient hole transport or electron blocking layer. Photoluminescence quantum yield (PLQY) measurements (Figure 4) revealed that optimal energy level alignment between perovskite/D18-Cl/spiro-OMeTAD reduces interfacial energy loss and improves charge transfer. The ITO/SnO2/perovskite(D18-Cl)/OAI stack showed a PLQY of 1.3%, lower than the control perovskite (CB) stack (3.34%), indicating that charge extraction dominates at the perovskite/D18-Cl interface rather than chemical passivation. However, after adding spiro-OMeTAD, the perovskite (D18-Cl) device exhibited a higher PLQY than the control, suggesting that D18-Cl reduces recombination across the interface rather than directly passivating the perovskite surface. This results in reduced interfacial losses due to well-matched band alignment in the perovskite/D18-Cl/spiro-OMeTAD stack.
1. GIWAXS analysis revealed that D18-Cl exhibits superior π-π stacking, facilitating the formation of a compact and dense thin film.
2. The HOMO of D18-Cl aligns well with the valence band maximum (VBM) of perovskite and the HOMO of home-grown hole-transporting layer (HTL), spiro-OMeTAD, resulting in improved charge extraction.
3. Steady-state photoluminescence (PL) and time-resolved photoluminescence (TRPL) measurements confirmed that D18-Cl enhances hole extraction efficiency.
Building on our OPV experience, we successfully incorporated D18-Cl on the perovskite surface to passivate interface trap states. While the one-step spin-coating process with antisolvent pipetting is widely used to control perovskite nucleation and crystallization, surface defects often lead to poor interfaces with charge-transport layers. To address this, we introduced D18-Cl into the antisolvent as a template agent, achieving high PCE even without additives in spiro-OMeTAD. This approach effectively modifies the perovskite/spiro-OMeTAD interface, enabling a simple and efficient antisolvent engineering technique.
Achievement 1: Using the anti-solvent film deposition method, we fabricated perovskite solar cells with the structure: ITO/SnO2/perovskite/OAI/spiro-OMeTAD/gold. After testing concentrations from 0.5 to 2.5 mg/ml, 1 mg/ml of D18-Cl was found optimal. The device performance (Figure 1) were compared for two antisolvent conditions: (1) pure CB (control) and (2) CB with 1 mg/ml D18-Cl. Both used identical HTL conditions without additives. Perovskite (D18-Cl)-based devices showed a 0.07 V increase in voltage, reducing recombination losses, and an fill factor rise from 75% to over 81%, improving charge extraction. This approach increased the efficiency from below 19% to over 23%.
Task 2: It is crucial to investigate the role of D18-Cl in the perovskite antisolvent. This includes performing various surface analyses, such as XRD, XPS, UPS, ToF-SIMS, FTIR, and SEM, alongside optical and electrical characterizations, to evaluate any changes in the perovskite's properties and surface. A key aspect of this work is determining whether the polymer remains on the perovskite surface or penetrates into its bulk. To explore this further, we also conducted X-ray reflectivity (XRR) and Neutron reflectivity (NR) measurements.
Achievement 2: From XRR and NR measurements (Figure 2), we identified an ultra-thin (1.2 nm) pure polymer layer on top and a 10 nm mixed region (D18-Cl and perovskite) underneath. These layers support proper energy level alignment and charge transport. UPS analysis (Figure 3) revealed that without the polymer, strong charge transfer (dipole size: 0.52 eV) occurs at the perovskite/spiro-OMeTAD interface, potentially leading to spiro-OMeTAD dedoping. With the polymer, weaker charge transfer (dipole size: 0.15 eV) occurs, reducing dedoping. The potential gradient in the D18-Cl layer promotes hole transport from the perovskite to the anode while blocking electrons, suggesting that D18-Cl acts as an efficient hole transport or electron blocking layer. Photoluminescence quantum yield (PLQY) measurements (Figure 4) revealed that optimal energy level alignment between perovskite/D18-Cl/spiro-OMeTAD reduces interfacial energy loss and improves charge transfer. The ITO/SnO2/perovskite(D18-Cl)/OAI stack showed a PLQY of 1.3%, lower than the control perovskite (CB) stack (3.34%), indicating that charge extraction dominates at the perovskite/D18-Cl interface rather than chemical passivation. However, after adding spiro-OMeTAD, the perovskite (D18-Cl) device exhibited a higher PLQY than the control, suggesting that D18-Cl reduces recombination across the interface rather than directly passivating the perovskite surface. This results in reduced interfacial losses due to well-matched band alignment in the perovskite/D18-Cl/spiro-OMeTAD stack.
1. Thick polymeric films typically have poor contact with the perovskite surface when applied via spin-coating, making it challenging to achieve an ultra-thin pure polymer layer. However, we were able to accomplish this by refining the antisolvent strategy and selecting the appropriate materials.
2. Spiro-OMeTAD, due to its low electrical conductivity, is typically doped with lithium bis(trifluoromethane)sulfonimide (LiTFSI) to enhance conductivity, but this requires a time-consuming in-situ oxidation process, making it hard to control the amount of oxidation. Alternative methods such as producing stable spiro-OMeTAD2·+(TFSI−)2 radicals can control doping without air oxidation. However, these still require additives like 4-tert-butylpyridine (tBP) to adjust energy level alignment with perovskite, which can degrade under humidity and heat and reduce the spiro-OMeTAD's glass transition point, affecting device stability. Our study eliminates harmful additives by modifying the perovskite surface with stable, hydrophobic organic polymers (D18-Cl), achieving better energy level alignment and improved performance in spiro-OMeTAD-based perovskite devices without compromising stability.
2. Spiro-OMeTAD, due to its low electrical conductivity, is typically doped with lithium bis(trifluoromethane)sulfonimide (LiTFSI) to enhance conductivity, but this requires a time-consuming in-situ oxidation process, making it hard to control the amount of oxidation. Alternative methods such as producing stable spiro-OMeTAD2·+(TFSI−)2 radicals can control doping without air oxidation. However, these still require additives like 4-tert-butylpyridine (tBP) to adjust energy level alignment with perovskite, which can degrade under humidity and heat and reduce the spiro-OMeTAD's glass transition point, affecting device stability. Our study eliminates harmful additives by modifying the perovskite surface with stable, hydrophobic organic polymers (D18-Cl), achieving better energy level alignment and improved performance in spiro-OMeTAD-based perovskite devices without compromising stability.