Optical Designs For Organic Photovoltaics

The research field of organic solar cells is booming due to the unique features such as tunable properties,cheap cost,roll-to-roll(R2R)compatiblity,light weight,and flexibility.As the core of organic solar cells,organic semiconductors can achieve different optical properties through molecule designs.In addition,although their optical thicknesses are limited by the generally low mobilities,organic thin films are consequently semitransparent.Therefore,organic photovoltaics shows great potential for application as power generating windows for buildings.Due to these characteristics,the optical designs for organic solar cells are important,various,and can be complicated.In this thesis,we focus on the optical properties of materials and the application scenarios of devices,and investigate the optical designs for organic photovoltaics mainly from the following three aspects:In chapter 2,through the combined contributions from the derivations of film stacks with arbitrary combinations of optical coherent and incoherent layers,deep algorithm optimizations,and analysis methods for various optical properties,we establish a effective multifunctional model for analysis of film optics,which can be used for optical properties of organic photovoltaics.This model can support for multiple device structures.In addition,we demonstrate the high operating speed(over 10,000 devices per second)of this model through a high-throughput simulation for the photonic crystal-enhanced semitransparent organic solar cells(PC-enhanced STOSCs),and highlight it can efficiently deal with complicated optical design problems.We translate the optical designs for organic photovoltaics into mathematical problems through optical model,and lay solid theory foundation for the follow-up researches.In chapter 3,based on the simulations,we systematically study the optical utilization and optical losses of a series of STOSCs.As the sum of external quantum efficiency(EQE)and transmittance(T),the quantum utilization efficiency(QUE)can not only uniformly describe the contradictory lighting harvesting and transmittance properties of device,but also indirectly reflect the opposite optical utilization and loss of device.We highlight the possibility of using this newly proposed concept as a subjective parameter to describe the light energy use in the semitransparent devices,which provides an alternative angle for analyzing STOSCs,and a concise method for verifying the accuracy of measurments for STOSCs.In chapter 4,for the first time,we proposed a high-throughput optical engineering strategy to design novel PC-enhanced STOSCs with optimal performance.According to the simulations,few selected paired PC-enhanced real STOSC devices with 9.88-11.25% power conversion efficiency(PCE)and 37.2-21.5% visible light transmittance(VLT)were successfully fabricated.According to the study for the quantum and optical properties of the devices,we define the PCE retaining ratio(PRR)as the ratio of the PCEs of the semitransparent device and its corresponding opaque device.We find that the PRR-VLT optimum curve can be simulated only through the optical constants.Thus,this curve can qualitatively describe the relationship between the optical properties of the photoactive layer and its corresponding device.The simulation-guided real device with around 30% VLT can achieve around 90% PRR,indicating its excellent optical performance.Because this work mainly comes from the viewpoint of optics,our methods and conclusions may also be instructive for research into other photovoltaic technologies.Moreover,our work shows the powerful role of the high-throughput engineering in extensive photovoltaic optical designs,especially for challenges such as multi-objective(PCE and VLT)and multi-layer thickness(six variable thicknesses)optimizations,exhibiting its wide potential applications.