Electron Transport Layer-free Solar Cells Research Articles

Construction of Effective Polymer Solar Cell Using 1,7-Disubstituted Perylene Diimide Derivatives as Electron Transport Layer.

The poor compatibility of an inorganic electron transport layer with the active layer and an ultrathin film organic material becomes a great obstacle in producing high-quality polymer solar cells with high-throughput roll-to-roll (R2R) method. Novel effective polymer solar cells had been fabricated by introducing 1, 7-disubstituted perylene diimide derivatives PDIH, PDIC, and PDIN as an electron transporting layer. It was noteworthy that PDIN could obviously improve the power conversion efficiency of solar cells that incorporated a photoactive layer composed of poly[(3-hexylthiophene)-2, 5-diyl] (P3HT) and the fullerene acceptor [6, 6-phenyl-C71-butyric acid methyl ester] (PC71BM). The power conversion efficiency varies from 1.5% for ZnO transparent cathode-based solar cells to 2.1% for PDIN-based electron transport layer-free solar cells. This improved performance could be attributed to the following reasons: the interaction between N atom in PDIN and O atom in indium tin oxide (ITO) reduced the work function of ITO, increased the built-in electric field, and thus lowered the electron transport barrier and improved the electron extraction ability of cathode, the appropriate roughness of the active layer increased the contact area with anode interfacial layer and enhanced the hole transport efficiency. These experimental results revealed that PDIN can be a promising novel effective material with a simplified synthesis process and lower cost as an electron transporting layer.

Carrier Dynamics Engineering for High-Performance Electron-Transport-Layer-free Perovskite Photovoltaics

Summary Electron-transport-layer-free (ETL-free) device architectures are promising designs for perovskite photovoltaics because they offer simpler configurations, low cost, and convenience for versatile optoelectronics. However, the development of ETL-free photovoltaics is hindered by their low performance. Herein, we reveal that a low electron-injection rate at the ETL-free interface is responsible for the performance loss. Moreover, we demonstrate that improving carrier lifetimes in the perovskite films can remedy the poor carrier extraction at interfaces, enabling carrier collection efficiency in ETL-free photovoltaics to approach that in ETL-containing devices. Using perovskite films with microsecond carrier lifetimes, we obtained ETL-free devices with a power conversion efficiency (PCE) of 19.5%, nearly eliminated hysteresis, and good stability. Such a PCE value is comparable to that (20.7%) of the analogous ETL-containing photovoltaics. These results offer opportunities for ETL-free architecture designs in the perovskite photovoltaics family. More importantly, this research provides a general approach to improving the performance of photovoltaics with low-injection-rate interfaces.

Electron transport layer-free polymer solar cells show 40% higher efficiency than using ZnO transparent cathode

The poor compatibility of inorganic materials (electron transport layer) with the active layer and an ultrathin film of conjugated polymers becomes the great obstacle to producing high-quality polymer solar cells with high-throughput roll-to-roll (R2R) method. Novel electron transport layer-free polymer solar cells have been constructed by integrating the conjugated aminoalkyl-functionalized polymer, poly[3-(5-(9,9-bis(3-(dimethylamino)propyl)-7-methyl-9H-fluoren-2-yl)thiophen-2-yl)-2,5-bis(2-butyloctyl)-6-(5-methylthiophen-2-yl)pyrrolo[3,4-c]pyrrole-1,4(2H,5H)-dione] (PDTFN) into the active layer. PDTFN was synthesized by different Suzuki reaction conditions to gain different molecular weights- small molecular weight (PDTFN-L) and high molecular weight (PDTFN-H). It is noteworthy that PDTFN-H can significantly enhance the power conversion efficiency of the solar cells that incorporate a photoactive layer composed of poly[(3-hexylthiophene)-2,5-diyl] (P3HT) and the fullerene acceptor [6,6-phenyl-C71-butyric acid methyl ester] (PC71BM). The power conversion efficiency varies from 2.5% for ZnO transparent cathode based solar cells to 3.6% for PDTFN-H based electron transport layer-free solar cells. This improved performance can be attributed to the following reasons: the PDTFN-H can enhance cathode electron transporting by introducing the PDTFN-H into active layer without extra coating the cathode interfacial material; besides, a favorable vertical phase separation of active layer was formed due to the PDTFN-H excellent compatibility with the bulk-heterojunction. These experimental results revealed that the electron transport layer-free polymer solar cells based on PDTFN-H can be a promising novel effective fabrication with simplified manufacturing process and lower cost.

Co-Solvent Effect in the Processing of the Perovskite:Fullerene Blend Films for Electron Transport Layer-Free Solar Cells

An understanding of the improvements achieved in the use of cosolvents for methylammonium lead triiodide (MAPbI3):C70 blend films (MAPbI3:C70) processing is presented. A comparative study using aromatic (i.e., o-xylene and o-dichlorobenzene) and aliphatic (i.e., methylcyclohexane and chlorocyclohexane) cosolvents proves the nature of the cosolvent interacting with fullerene to be determining for achieving enhanced devices. UV–vis spectra of the different C70 solutions suggest a major impact of the solute–aromatic solvent interactions on the optoelectronic properties. The effect of aromatic and aliphatic solvents in the electronic structure of C70 crystals, obtained from the different solutions, is indeed demonstrated by electron energy loss spectroscopy. Morphological studies show elimination of pinholes (field emission scanning electron microscopy) and different nanometric features related to fullerene (atomic force microscopy) in MAPbI3:C70 blend films processed using aromatic cosolvents. A severe quenc...

(Invited) Efficient Electron Transport Layer-Free Solar Cells Based on Innovative Perovskite:Fullerene Blends

A variety of novel fullerene materials, showing different electron accepting capabilities, has been synthesized and used to prepare electron transport layer-free solar cells based on CH3NH3PbI3:fullerene blends. The photovoltaic study performed over a series of devices verifies the suitability of this electron transport layer-free strategy as a promising alternative to build efficient solar cells avoiding the use of TiO2. Furthermore, clear correlation between the LUMO of the fullerene material and the open circuit voltage of the solar cells is found.