Highly Efficient Indoor Organic Solar Cells by Voltage Loss Minimization through Fine-Tuning of Polymer Structures

Abstract

Herein, we report a detailed study on the optoelectronic properties, photovoltaic performance, structural conformation, morphology variation, charge carrier mobility, and recombination dynamics in bulk heterojunction solar cells comprising a series of donor–acceptor conjugated polymers as electron donors based on benzodithiophene (BDT) and 5,8-bis­(5-bromothiophen-2-yl)-6,7-difluoro-2,3-bis­(3-(octyloxy)­phenyl)­quinoxaline as a function of the BDT’s thienyl substitution (alkyl (WF3), alkylthio (WF3S), and fluoro (WF3F)). The synergistic positive effects of the fluorine substituents on the minimization of the bimolecular recombination losses, the reduction of the series resistances (R S), the increment of the shunt resistances (R Sh), the suppression of the trap-assisted recombination losses, the balanced charge transport, the finer nanoscale morphology, and the deeper highest occupied molecular orbital (E HOMO) are manifested versus the alkyl and alkylthio substituents. According to these findings, the WF3F:[6,6]-phenyl-C71-butyric acid methyl ester (PC71BM)-based organic photovoltaic device is a rare example that features a high power conversion efficiency (PCE) of 17.34% under 500 lx indoor light-emitting diode light source with a high open-circuit voltage (V OC) of 0.69 V, due to the suppression of the voltage losses, and a PCE of 9.44% at 1 sun (100 mW/cm2) conditions, simultaneously.

An Overview of High‐Performance Indoor Organic Photovoltaics

“…[18] Singh et al investigated the substituent effects on the performance of donor based on benzodithiophene (BDT) and 5,8-bis(5-bromothiophen-2-yl)-6,7difluoro-2,3-bis(3-(octyloxy)phenyl)quinoxaline. [30] As a result, the fluorine substituent (WF3F) on the BDT thienyl showed great improvement in properties when compared with alkyl-(WF3) and alkylthio-(WF3S) substituents, showing a larger optical bandgap. Under 1 sun illumination, WF3:PC 71 BM, WF3S: PC 71 BM, and WF3F:PC 71 BM OSCs with diphenyl ether (DPE) additive exhibited PCEs of 7.71, 7.91, and 9.11 %, respectively.…”

“…Under LED illumination of 500 lx, the devices showed PCEs of 12.83, 14.32, and 17.34 %, respectively. [30] Fullerene-based IOPVs have made great progress in recent years mainly ascribed to the development of large-bandgap donors. Generally, synthesizing wide-bandgap organic semiconductors with high absorption coefficients for further improving the performance of IOPVs is required.…”

Indoor Organic Photovoltaics for Self‐Sustaining IoT Devices: Progress, Challenges and Practicalization

“…In last few years, medium bandgap polymer/small molecule donors with fullerene-based acceptors reported IOPVs having PCEs of 8-28 % under indoor light illumination conditions. [14,17,19,[60][61][62] Yang et al investigated the P3HT polymer with different fullerene derivatives (PC 60 BM and ICBA) and obtained PCEs of 8.90 and 13.05 % for P3HT:PC 60 PB and P3HT:ICBA photoactive layers respectively, under 500 lux LED lamp. [60] The high performance of P3HT with ICBA compared to PC 60 BM acceptor material is due to better energy alignment.…”

“…As a result, WF3F:PC 71 BM BHJ can exhibit a PCE of 17.34 % with V OC : 0.69 V under 500 lux LED source. [62] Moreover, Shim et al demonstrated PDTBTBz-2F anti : PC 71 BM OPVs which exhibits an excellent spectrum matching with indoor lighting environment, resulting in an excellent power absorption ratio. [63] These optical properties contribute to performance of the PDTBTBz-2F anti :PC 71 BM based IOPVs with a high PCE of 23.1 % having V OC : 0.81 V under 1000 lux LED illuminations.…”

Thick‐Film Low Driving‐Force Indoor Light Harvesters

“…[ 1–6 ] An ideal bulk heterojunction (BHJ) adopted for indoor light harvesters should satisfy both the requirements of device performance and fabrication feasibility. [ 7–12 ] The power conversion efficiency (PCE) of IPV cells can be optimized by adjusting donor:acceptor (D:A) materials and weight fractions for the spectral matching with the indoor light sources (e.g., fluorescence, light‐emitting diode [LED], incandescent, and halogen lamps) and suitable energy levels. Together with appropriate solar cell fabrication methods, the open‐circuit voltage ( V oc ), short‐circuit current density ( J sc ), and fill factor (FF) values can be maximized under indoor light emissions.…”