11% Organic Photovoltaic Devices Based on PTB7‐Th: PC₇₁BM Photoactive Layers and Irradiation‐Assisted ZnO Electron Transport Layers

Abstract

The enhancement of interfacial charge collection efficiency using buffer layers is a cost‐effective way to improve the performance of organic photovoltaic devices (OPVs) because they are often universally applicable regardless of the active materials. However, the availability of high‐performance buffer materials, which are solution‐processable at low temperature, are limited and they often require burdensome additional surface modifications. Herein, high‐performance ZnO based electron transporting layers (ETLs) for OPVs are developed with a novel g‐ray‐assisted solution process. Through careful formulation of the ZnO precursor and g‐ray irradiation, the pre‐formation of ZnO nanoparticles occurs in the precursor solutions, which enables the preparation of high quality ZnO films. The g‐ray assisted ZnO (ZnO‐G) films possess a remarkably low defect density compared to the conventionally prepared ZnO films. The low‐defect ZnO‐G films can improve charge extraction efficiency of ETL without any additional treatment. The power conversion efficiency (PCE) of the device using the ZnO‐G ETLs is 11.09% with an open‐circuit voltage (V OC), short‐circuit current density ( J SC), and fill factor (FF) of 0.80 V, 19.54 mA cm‐2, and 0.71, respectively, which is one of the best values among widely studied poly[4,8‐bis(5‐(2‐ethylhexyl)thiophen‐2‐yl)benzo[1,2‐b;4,5‐b′]dithiophene‐2,6‐diyl‐alt‐(4‐(2‐ethylhexyl)‐3‐fluorothieno[3,4‐b]thiophene‐)‐2‐carboxylate‐2‐6‐diyl)]: [6,6]‐phenyl‐C71‐butyric acid methyl ester (PTB7‐Th:PC71BM)‐based devices.

Lead Halide Perovskite Quantum Dots To Enhance the Power Conversion Efficiency of Organic Solar Cells

“…It is worth emphasizing that the optimized addition of CsPbI 3 QDs (3 wt %) yields an enhancement in the PCE of 35 % relative to the control device, which is the highest increase reported amongst hybrid ternary devices (Supporting Information, Table S3), and more importantly, the efficiency of 10.84 % obtained with our champion device stands out among the highest for devices based on the light harvesting of a PTB7‐Th:PC 71 BM blend …”

Lead Halide Perovskite Quantum Dots To Enhance the Power Conversion Efficiency of Organic Solar Cells

“…More specifically, the photogenerated electron lifetime under open circuit conditions can be estimated with this technique by monitoring the photovoltage response to asmall sinusoidal modulation of the light intensity.F igure 6a shows the Nyquist plots of the IMVS measurements performed on devices with increasing QD loading, which show as emi-circular arc in the complex plane with as light cardioid shape at high-frequencies (near the origin) that is likely related to the RC-attenuation of the circuit in this frequency range.Onthe basis of the theoretical description of IMVS, [57] the characteristic angular frequency at the critical point of the Nyquist plot (the minimum imaginary component value), as highlighted for each plot in Thedependence of the extracted t rec as afunction of the QD loading is displayed in Figure 6b.A so bserved, the device without QDs shows a t rec of 2.6 ms, similar to that previously reported. [44] Upon the incorporation of QDs, t rec rises significantly,p eaking at 7.1 msf or 3wt%,a nd subsequently decreases with further QD loading.I nterestingly,t he trend observed in t rec correlates quite well with the PCE, matching the optimum performance with the longest lifetime.T his is consistent with reports in other systems where increasing carrier lifetimes have been reported to be associated with an improved PCE. [44] It is important to clarify the nature of the recombination pathway that is monitored with IMVS.T ransient absorption spectroscopy studies performed on various polymer/fullerene blends under open circuit conditions have systematically demonstrated that monomolecular recombination starts quickly after photo-excitation extending to the hundreds of nanoseconds timescale,w hereas the bimolecular recombination of dissociated charges extends over the microsecond timescale.…”

“…[44] Upon the incorporation of QDs, t rec rises significantly,p eaking at 7.1 msf or 3wt%,a nd subsequently decreases with further QD loading.I nterestingly,t he trend observed in t rec correlates quite well with the PCE, matching the optimum performance with the longest lifetime.T his is consistent with reports in other systems where increasing carrier lifetimes have been reported to be associated with an improved PCE. [44] It is important to clarify the nature of the recombination pathway that is monitored with IMVS.T ransient absorption spectroscopy studies performed on various polymer/fullerene blends under open circuit conditions have systematically demonstrated that monomolecular recombination starts quickly after photo-excitation extending to the hundreds of nanoseconds timescale,w hereas the bimolecular recombination of dissociated charges extends over the microsecond timescale. [58][59][60] This suggests that the t rec extracted from the IMVS data corresponds to the kinetics of bimolecular recombination.…”

“…It is worth emphasizing that the optimized addition of CsPbI 3 QDs (3 wt %) yields an enhancement in the PCE of 35 %r elative to the control device,w hich is the highest increase reported amongst hybrid ternary devices (Supporting Information, Table S3), [8,10,12,14] and more importantly,the efficiency of 10.84 %o btained with our champion device stands out among the highest for devices based on the light harvesting of aP TB7-Th:PC 71 BM blend. [43,44] Figure 2b shows the incident photon-to-current efficiency (IPCE) spectra obtained for the devices containing 0t o 3wt% (IPCE spectra for higher QD loading can be found in the Supporting Information, Figure S5), and the electron flow predicted from the IPCE and the AM 1.5 Gs tandard solar spectrum is included in Figure 2c.Asexpected, the values of IPCE increase in agreement with the observed enhancement in J sc ,albeit only within certain regions of the spectra. Indeed, the IPCE spectra barely changes in the range from 680-800 nm whereas the values clearly improve at lower wavelength with increasing QD loadings.T his localized enhancement with the incorporation of QDs can also be observed in the spectral regions centered around 2.0 eV and 2.6 eV ( Figure 2c).…”

“…Intensity-modulated photovoltage spectroscopy (IMVS) is af requency-domain perturbation technique that has been successfully employed to characterize recombination dynamics in various photovoltaic devices (for example,d ye-sensitized, [54] perovskite-based, [55] or OSCs [44,56] ). More specifically, the photogenerated electron lifetime under open circuit conditions can be estimated with this technique by monitoring the photovoltage response to asmall sinusoidal modulation of the light intensity.F igure 6a shows the Nyquist plots of the IMVS measurements performed on devices with increasing QD loading, which show as emi-circular arc in the complex plane with as light cardioid shape at high-frequencies (near the origin) that is likely related to the RC-attenuation of the circuit in this frequency range.Onthe basis of the theoretical description of IMVS, [57] the characteristic angular frequency at the critical point of the Nyquist plot (the minimum imaginary component value), as highlighted for each plot in Thedependence of the extracted t rec as afunction of the QD loading is displayed in Figure 6b.A so bserved, the device without QDs shows a t rec of 2.6 ms, similar to that previously reported.…”