The Research Of Inverted Polymer Solar Cells With High Efficiency And Stability

Polymer solar cells (PSCs) have attracted extensive attention due to their potential applications in terms of cost, scalability and environmental impact. Solution-processability of PSCs makes it possible to be manufactured by high-throughput roll-to-roll processes. Over the past few years, enormous progress has been achieved on improving the performance of PSCs via designing new photovoltaic materials, optimizing device fabrication conditions, developing new device structures and engineering contact interface. Recently the power conversion efficiency (PCE) of the PSCs has reached7-9%. However, the PCE and lifetime of the PSCs still need to be further improved for their future application.The conventional bulk-heterojunction (BHJ) PSCs are typically fabricated with a photoactive layer sandwiched between a modified transparent conductive anode (e.g. indium tin oxide, ITO) and a low-work-function metal cathode (e.g., Ca)/Al. The low-work-function metals are vulnerable to oxygen and water, which lead to device degradation and failure. For the modification of anode, poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate)(PEDOT:PSS) is the commonly used interfacial material, showing good electrical properties and processability. However, the acidic PEDOT:PSS can etch ITO, causing the problems with respect to morphology uniformity and chemistry stability.To overcome these problems, inverted polymer solar cells have been developed, in which stable ITO is used as the cathode to collect electrons and the device polarity is reversed. The performance of the inverted PSCs is critically dependent on the choice of the interfacial layers, on the contact properties with the BHJ layer, and on the corresponding electrodes. In the inverted architecture, significant improvements in stability and efficiency can be achieved by using the air stable low-work-function interfacial materials as electron collection layer, such as titanium oxide (TiOx), zinc oxide (ZnO), and cesium carbonate (CS2CO3). Nevertheless, most research carried out on these solution-processed electron collection materials required a high annealing temperature (higher than200℃) to form a crystallized film, which is not suitable for fabrication of flexible PSCs with polymer substrate.In order to solve these restrictions mentioned above, We demonstrate efficient inverted polymer solar cells (PSCs) based on poly(3-hexylthiophene)(P3HT) and [6,6]-phenyl-C61-butyric acid methyl ester (PCBM) by using solution-processed titanium(IV) oxide bis(2,4-pentanedionate)(TOPD) as electron collection layer (ECL) between the indium tin oxide (ITO) electrode and photoactive layer. The TOPD buffer layer was prepared by spin-coating isopropanol solution of TOPD on ITO and then baked at140癈for5min. The power conversion efficiency (PCE) of the inverted PSC with TOPD buffer layer reaches4.0℃under the illumination of AM1.5G,100mW/cm2, which is increased by76%in comparison with that (2.27%) of the inverted device without TOPD ECL. Moreover, we further study the applicability of TOPD as ECL into other photo-active system. It also shows a better performance with a7.14%PCE achieved for the inverted PSC based on TOPD as ECL and low band-gap donor PBDTTT-C blended with PCBM as photo-active layer. The results indicate that TOPD is a promising electron collection layer for inverted PSCs.