Yongbing Long

Semitransparent Polymer Solar Cells with 5% Power Conversion Efficiency Using Photonic Crystal Reflector

Efficient semitransparent polymer solar cells (ST-PSCs) have been fabricated with one-dimensional photonic crystals (1DPCs) as a high reflector. The 1DPCs are composed of several pairs of WO3 (65.8 nm)/LiF (95.5 nm). By optimizing the pairs of WO3/LiF, 1DPCs can reflect the light back into the ST-PSCs due to the photonic band gap, when the high reflectance range of 1DPCs is matched with absorption spectrum of the active layer. ST-PSCs with 8 pairs of 1DPC exhibit an attractive performance. The short-circuit current density (Jsc) and power conversion efficiency (PCE), respectively, reach to 9.76 mA/cm(2) and 5.16% compared to 8.12 mA/cm(2) and 4.24% of the reference ST-PSCs without 1DPCs. A maximum enhancement of 20.2% in Jsc is obtained and the PCE increases by ~21.7%. This approach provides a simple, fascinating and promising method to realize the highly efficient ST-PSCs toward applications.

Highly Efficient Semitransparent Polymer Solar Cells with Color Rendering Index Approaching 100 Using One-Dimensional Photonic Crystal

Window application is the important aim for semitransparent solar cells (STPSC) investigation. Here, we demonstrate a method to achieve significantly improved color rendering index (CRI), depressed chromaticity difference (DC), and enhanced power conversion efficiency (PCE) simultaneously by introducing the one-dimensional photonic crystals (1DPCs) Bragg reflector structure onto the STPSC. The device performance is studied from aspects of color perception, electrical properties, and theoretical optical simulations. The STPSCs exhibit achromatic transparency nature color perceptions, especially for the STPSCs with 1DPCs (pairs ≥ 3) under AM 1.5G illumination light source, standard illuminant D65, and standard illuminant A. The excellent CRI is approaching 97 with lower DC about 0.0013 for the device with 5 pairs of 1DPC illumined by AM 1.5G illumination light source. At the same time, the PCE of STPSC devices with 5 pairs of 1DPC was improved from 4.87 ± 0.14% to 5.31 ± 0.13% compared to without. This method provides a facilitative approach to realizing excellent SPTSC window application.

Semitransparent polymer solar cells with one-dimensional (WO3/LiF)N photonic crystals

One-dimensional (WO3/LiF)N photonic crystals (1DPCs) are deposited on the Ag cathode of the semitransparent polymer solar cells to improve the efficiency of the device. The 1DPCs with 8 pair of WO3/LiF act as distributed reflectors within the photonic bandgap. Then, power conversion efficiency of 2.58% is achieved and there is an improvement of 26.3% in the efficiency when compared with that of the conventional device without the 1DPCs. The average transmittance of the device with 8 pair of WO3/LiF is almost zero in 400–600 nm wavelength range. It means that the light is absorbed sufficiently in the active layer. The enhanced light absorption results in efficiency improvement remarkably.

Performance Improvement of Low-Band-Gap Polymer Solar Cells by Optical Microcavity Effect

We investigate the performance of the indium tin oxide (ITO)-free low-band-gap polymer solar cells (PSCs) with a WO3/Ag/WO3 multilayer as a transparent electrode. For the device with a 60-nm-thick active layer, the efficiency is improved by 26.5% when compared with that of the device with an ITO electrode. The improvement can be attributed to the resonance effect of the microcavity structure occurring between the transparent WO3 /Ag/WO3 and top metal electrode. Further investigation based on the incident photon-to-electron conversion efficiency spectra test and transfer matrix simulation is performed to expatiate on the effects of the microcavity on the performance of the low-band-gap PSCs with the WO3/Ag/WO3 multilayer as the transparent electrode.

Indium Tin Oxide-Free Polymer Solar Cells: Microcavity Enhancing the Performance Using WO 3 /Au/WO 3 as Transparent Electrode

Recently, indium tin oxide (ITO)-free polymer solar cells (PSCs) have attracted increasing attention due to expensive ITO price caused by rare and valuable element-indium. Here, we fabricated and investigated ITO-free PSCs with the structure of glass/WO 3 /Au/WO 3 /poly (3-hexylthiophene): indene-C 60 bisadduct (P3HT:ICBA)/LiF/Al. It is demonstrated that the power conversion efficiency of ITO-free devices with 85-nm-thick active layer is improved by 21.2% compared with that of ITO-based. The improvement is attributed to the first-order resonance and near-resonance of microcavity effect constructed between the Au anode and top Al cathode. The judgment is supported by the incident photon-to-electron conversion efficiency spectra test and optical simulation based on transfer matrix method, which reveal that the microcavity structure can enhance light absorption within two discrete wavelength ranges of 390-460 and 510-660 nm.

Top-to-bottom optimization of the optical performance of the tandem organic solar cells with thin metal film as interlayer

Top-to-bottom optimization is developed to maximize the absorption for tandem organic solar cells with thin Ag interlayer connecting two subcells. By redshifting the cavity modes of the microcavity between the Ag interlayer and the top electrode, the absorptionspectrum of the top cell can be shifted to the near-infrared wavelength range where the bottom cell has weak absorption. Correspondingly, subcells with highly complementary absorptionspectrum are achieved, and there is an improvement of 17.8% in the total absorbed photons for the tandem device. Additionally, it is revealed that high transparency is not an essential property for the interlayer in tandem devices.

Decreased Charge Transport Barrier and Recombination of Organic Solar Cells by Constructing Interfacial Nanojunction with Annealing-Free ZnO and Al Layers

To overcome drawbacks of the electron transport layer, such as complex surface defects and unmatched energy levels, we successfully employed a smart semiconductor-metal interfacial nanojunciton in organic solar cells by evaporating an ultrathin Al interlayer onto annealing-free ZnO electron transport layer, resulting in a high fill factor of 73.68% and power conversion efficiency of 9.81%. The construction of ZnO-Al nanojunction could effectively fill the surface defects of ZnO and reduce its work function because of the electron transfer from Al to ZnO by Fermi level equilibrium. The filling of surface defects decreased the interfacial carrier recombination in midgap trap states. The reduced surface work function of ZnO-Al remodulated the interfacial characteristics between ZnO and [6,6]-phenyl C71-butyric acid methyl ester (PC71BM), decreasing or even eliminating the interfacial barrier against the electron transport, which is beneficial to improve the electron extraction capacity. The filled surface defects and reduced interfacial barrier were realistically observed by photoluminescence measurements of ZnO film and the performance of electron injection devices, respectively. This work provides a simple and effective method to simultaneously solve the problems of surface defects and unmatched energy level for the annealing-free ZnO or other metal oxide semiconductors, paving a way for the future popularization in photovoltaic devices.

Optimizing the light absorption of graphene-based organic solar cells by tailoring the weak microcavity with dielectric/graphene/dielectric multilayer

Investigation into the organic solar cells (OSCs) with graphene electrode demonstrates that the weak-microcavity (WMC) constructed between the transparent electrode and top metal electrode plays an important role in the absorption properties of the devices. If the WMC structure is not optimized, the absorption of the graphene-based devices cannot surpass that of OSC devices with indium tin oxide electrode. By employing dielectric/graphene/dielectric multilayer to optimize the WMC, the absorption can be improved by a maximum value of 21.1% within a broad wavelength range of 410–636 nm. Correspondingly, an improvement of 12.1% in total absorbed photons is achieved for the device.