Light Absorption In Active Layer Research Articles

Improving light absorption of active layer by adjusting PEDOT:PSS film for high efficiency Si-based hybrid solar cells

Ultrathin PEDOT:PSS film induces inversion layer within Si to achieve carrier separation, but it as the window-layer directly affects the light absorption. Herein, we show that management of reflectivity and parasitic absorption by adjusting PEDOT:PSS film thickness improves light absorption of active layer. According to the equivalent optical admittance theory and the finite element method, it is found that the reflectivity spectrum is divided into periodic and aperiodic regions by a certain wavelength threshold. When the threshold is close to 300 nm, the smaller reflection and parasitic absorption can be achieved. Meanwhile, with the increase of PEDOT:PSS film thickness, the quasi-Fermi level bending gradually weakens, and the hole concentration gradually keeps stable. This improves the carrier separation efficiency to reduce the carrier recombination, which ensures the improvement of solar cell performance. Finally, the power conversion efficiency (PCE) of 12.35% is obtained by applying the rule obtained from the simulation to the experiment, which is 30% higher than that of the unoptimized PEDOT:PSS/Si hybrid solar cell.

The preparation of plasmonic Au@SiO2 NPs and its application in polymer solar cells

We prepared plasmonic Au@SiO2 NPs with good quality and doped them into PEDOT: PSS layer of PC71BM-based PSCs. These Au@SiO2 NPs could greatly increase the light absorption of active layer mainly due to near field enhancement, thus resulting in an improved photocurrent. Finally, a maximum PCE of 9.55% with a 16.3% enhancement was achieved for PTB7-Th: PC71BM based devices, which is the highest value reported so far.

Dual-microcavity resonance and plasmon-cavity polaritons enhanced the broadband absorption of polymer-based organic solar cells by employing micro-nano composite gratings

Abstract A broadband-absorption enhancement in two kinds of polymer-based organic solar cells (OSCs) is demonstrated in this work by employing micro-nano composite gratings (MNCGs). The structure of MNCGs is nano-grating covering on the surface of micro-grating. By embedding the MNCGs at the interface of the active layer/Ag cathode, the multi-absorption-enhancement mechanisms, such as dual-microcavity resonance, plasmon-cavity polaritons and light-scattering effects, are excited and result in a broadband-absorption enhancement. The light absorption of active layer in the MNCG-based OSC is numerically calculated. As a result, comparing to the planar OSCs, the absorption intensity is increased by 50.41% and 20.43% in these two kinds of polymer-based OSCs, respectively. Meanwhile, the MNCGs can also be universally used in all kinds of polymer-based OSCs to increase the light absorption of the active layer.

Facilitating electron extraction of inverted polymer solar cells by using organic/inorganic/organic composite buffer layer

Abstract In this work, the performance of inverted polymer solar cells (PSCs) was enhanced by introducing an organic/inorganic/organic (OIO) composite electron-transporting layer (ETL) with the structure of poly ethylenemine(PEI)/SnO2/poly[(9,9-bis(30-(N,N-dimethylamino)propyl)-2,7-fluorene)-alt-2,7-(9,9-dioctylfluorene)] (PFN). The work function measurement and surface morphology indicate that OIO ETL modulates the energy level between active layer and cathode, and reduces the interfacial defects due to the poor contact between organic material and inorganic substance. Also, the OIO ETL could enhance the light absorption of active layer. Therefore, both a high short-circuit current density and fill factor are obtained in the devices owning an OIO ETL, which leads to a dramatic enhancement of device efficiency from 5.51% to 7.18%, accounting for a 30.30% increase. This novel concept of OIO ETL paves a new path for the future applications in the field of PSCs.

An easily prepared Ag8GeS6 nanocrystal and its role on the performance enhancement of polymer solar cells

Novel Ag8GeS6 nanocrystal materials (AGS NCs) have recently earned affectionate attention due to its bulk band-gap of 1.4 eV, which makes it ideal as a broad-spectrum absorber material for both semiconductor photocatalyst and photovoltaic devices. In this paper, we investigated the role of AGS NCs as molecular dopant on solution-processed polymer solar cells (PSCs). Argyrodite AGS NCs was prepared via a colloidal synthesis process using simple inorganic compounds as precursors. Incorporating AGS NCs into PSCs leads to not only improved light absorption of active layer but also increased phase separation of donor and acceptor. Moreover, the doping effect of AGS NCs was also confirmed by nanoscale morphology and photocurrent generation mechanism analysis, revealing that AGS NCs could serve as both exciton dissociation centers and charge transfer medium. This study shows that employment of AGS NCs is a facile way to improve the electrical and optical properties of organic photovoltaic devices.

Enhanced transmittance of metallic film with nanoaperture array

Metallic film as an indium tin oxide alternative, which shows excellent mechanical flexibility and high conductivity, has the ideal physical properties for flexible organic solar cells (OSCs). However, a bottleneck of metallic film was a lack of transmittance that limits the application in OSCs. We have demonstrated a nanoaperture metallic film fabricated by a template striping method, which can overcome the above-mentioned bottleneck. This metallic film has a random nanoaperture array. The size and shape of the nanoaperture were dependent on master templates. This metallic film with nanoaperture array is not only able to show high conductivity but also possesses tunable localized surface plasmon (LSP) resonance as well. The LSP could be coupled with dipole mode in nanostructure, which can account for the transmission enhancement and efficiently increase the light absorption of active layer in the OSCs. Moreover, this metallic film with nanoaperture array will exhibit particular advantage in flexible OSCs because the backing layer itself is a flexible substrate. The nanoaperture metallic film fabricated by this method as an electrode was a good choice for OSCs.

Theoretical studies on the influence of graphene layers as an anode on the performance of P3HT:PC61BM and PTB7:PC71BM bulk heterojunction organic solar cells

In the present work, photovoltaic properties of P3HT:PC61BM bulk heterojunction solar cells based on graphene anode are investigated using the transfer matrix model and drift-diffusion model for optical and electrical performances, respectively. First, we study the effect of the number of graphene layers on optical and electrical performance. Light absorption and total exciton generation rate in active layer as well as photovoltaic parameters including the short circuit current density, open circuit voltage, fill factor, and power conversion efficiency are determined. The optoelectronic model suggests that short circuit current density decreases upon increasing the number of graphene layers, which is attributed to the reduction of light absorption in the active layer. Power conversion efficiency is found to be between 3.49 and 4.31 % for various numbers of graphene layers. Based on the calculation results, five-layer graphene anode is found to have the same sheet resistance as 150 nm-thick ITO anode. Second, the performance of five-layer graphene-based organic solar cell is compared with that of ITO-based anode device. The results indicate that the former can reach 84 % power conversion efficiency of the latter. Finally, P3HT:PC61BM replaces with PTB7:PC71BM as the active layer and its influence on device performance is studied.

Optical absorption and electrical properties of enhanced efficiency in organic solar cells as interfacial layer with Au NPs

The effects of the gold nanoparticles (Au NPs) on performance of organic solar cells (OSCs) are systematically investigated based on blend of the low band gap polymer and fullerene. The localized surface plasmon resonance (LSPR) induced by the Au NPs enhance the light absorption in the active layer and the photoluminescence spectra showed a significant enhancement in their intensity which mainly contribute to increased light absorption of active layer induced by LSPR. The impedance spectroscopy study revealed that the introduction of Au NPs as interfacial layer decreases the sheet and charge-transport resistance between ITO/PEDOT:PSS or PEDOT:PSS/active layer. From the results, the introduction of Au NPs increased the rate of exciton generation and the probability of exciton dissociation, thus enhancing the short-circuit current density and the fill factor The optimized OSCs incorporated with Au NPs were found to have power conversion efficiency of 5.40% compared to control device (4.65%), measured by using an AM 1.5G solar simulator at 100mW/cm2 light illumination intensity.

Ultra-Thin Organic Solar Cells Incorporating Dielectric-Coated Comb Silver Nanogratings

Although coating engineering on metallic nanostructures has been frequently applied in organic solar cells (OSCs) for improving the device performance by preventing the possible exciton quenching and charge recombination at the metal surface, there have been few theoretical researches addressing how the dielectric-coating of metal nanostructures influences the optical performance of OSCs. Here, we theoretically investigate the effect of coating a comb silver nanograting by a dielectric film on the absorption performance of OSCs. It is found that, under transverse-magnetic (TM) polarization, when the refractive index or thickness of the dielectric-coating is tuned, different orders of plasmonic waveguide modes are excited by the P3HT:PC61BM/coating/Ag triple-layered system. The dispersion relationship of such a plamsonic waveguide mode is solved and analyzed for clarifying the physical mechanism of the induced light trapping effect. It shows that for optimizing the light absorption in active layer under TM polarization, it is more favorable to coat a thin dielectric film (of 1 nm thick) with a suitable refractive index. While under transverse-electric (TE) polarization, the higher refractive index of dielectric-coating, the better the effect of light trapping.

Versatile MoS2 Nanosheets in ITO-Free and Semi-transparent Polymer Power-generating Glass.

Chemical exfoliated ultra-thin MoS2 nanosheets (NSs) with well 2D structure were demonstrated for interfacial layers and Ag nanowires composite transparent electrode in polymer solar cells (PSCs). The smooth and uniform n-type and p-type (after the plasma treatment) MoS2 NSs could improve fill factor of devices and light absorption in active layer. The optimized Ag nanowires–MoS2 NSs (AgNW-MoS2 NSs) transparent electrode presented a low sheet resistance of 9.8 Ω sq−1, and the corresponding transmittance also exhibited a high value of 93.1% at 550 nm. As a result, ITO-free PSCs based on AgNW-MoS2 NSs/n-MoS2 NSs cathode and p-MoS2 NSs/Ag anode achieved a highest PCE of 8.72%. Furthermore, a high efficiency (6.55%), large area and low cost semi-transparent power-generating glass was obtained, after reducing the thickness of top Ag electrode from 100 nm to 30 nm. To our best knowledge, it is the highest performance for semi-transparent PSCs devices reported up to now. The novel semi-transparent power-generating glass showed good performance and color purity for commercial applications in the near future.

Improved performances of CuPc/C60-based solar cell by using randomly and irregularly embossed PEDOT:PSS as anode buffer layer

An unique organic solar cell (OSC) based on copper phthalocyanine (CuPc) and fullerene C60 as the electron donor and acceptor materials is demonstrated with randomly and irregularly embossed poly (3, 4-ethylenedioxythiophene) poly (styrenesulfonate) (PEDOT: PSS) as anode buffer layer. The effect of PEDOT:PSS nanostructure is characterized by optical and electrical measurements. The results indicate that introducing irregular nanostructure with random distribution into OSC leads to longer light paths by efficient scattering of the incident light and thus higher light absorption in active layer. Moreover, such a nanostructure increases the junction area, allowing more efficient exciton dissociation and charge carrier transfer/collection. These combined effects result in a prominent enhancement of 25.5% in average power conversion efficiency relative to the non-structured OSC due to the increases in short-circuit current and fill factor.

Surface plasmon enhanced organic solar cell with different silver nanosphere sizes.

We have systematically investigated the plasmonic effects on the characteristics of OPV devices of a blend of poly(3-hexylthiophene) (P3HT) and [6,6]-phenyl-C61-butyric acid methyl ester (PCBM) as well as of blend of polymer poly[2,1,3-benzothiadiazole-4,7-diyl[4,4-bis(2-ethylhexyl)-4H-cyclopenta [2,1-b:3,4 b']dithioph-ene-2,6-diyl]] (PCPDTBT) and PCBM with an incorporated thin silver (Ag) film. Silver nanospheres (NSs) were introduced through a solution casting process to improve the performance of bulk-heterojunction organic solar cells. The Ag NSs with variable sizes were investigated, with the aim of optimizing the performance of devices. The power conversion efficiency (PCE) increases by a maximum 14% for the 40 nm Ag NSs. The larger-sized Ag NSs used in this study led to a larger enhancement of short circuit current JSC and PCE. Analysis of the changes in electronic performance leads to the conclusion that the plasmonic light trapping scheme improves the performance of OPV devices. This is caused by the increases of both fill factor and JSC, whilst open circuit voltage VOC remains relatively constant. These enhancements are mainly due to the localized surface plasmon resonance and light scattering of metal nanoparticles, which increase the light absorption of active layer and improve the exciton generation and dissociation.

Effect of textured electrodes with light-trapping on performance of polymer solar cells

Textured electrodes with rough surface in combination with reflective back contacts provide efficient light-trapping by light scattering and multiple reflections to increase the path length of the light, and the resulting enhanced efficiency of organic photovolatics. In this paper, the effect of textured electrodes with different surface morphology on the performance of polymer solar cells was investigated. Two kinds of textured SnO2:F (FTO) electrodes possessing “V” (V-FTO) and “U” (U-FTO) topography, respectively, were used as the front electrodes of polymer solar cells. Due to the enhanced light absorption in active layer, the resultant cells with U-FTO and V-FTO showed 9% and 6% improvement in short current density (Jsc), respectively, compared with the flat FTO electrode. The U-FTO electrode was amenable to coating a conformal buffer layer and preferred to obtain high efficient cells. However, the enhanced Jsc of the V-FTO cells did not contribute to the improved efficiency for the decreased fill factor and open circuit voltage.

Efficient polymer solar cells based on light-trapping transparent electrodes

Highly efficient and cost-effective polymer solar cells (PSCs) fabricated on textured fluorine doped transparent conductive (FTO) electrodes are achieved. Such electrodes with rough surface in combination with reflective back contacts provide efficient light-trapping by light scattering and multiple reflections to increase the path length of the light. Due to the increased light absorption in active layer, the resultant PSCs base on polymer:fullerene system show 10% and 8% improvement in short current density and efficiency, respectively, compared with the reference cell based on the flat electrodes.