Controlling Energy Levels and Blend Morphology for All-Polymer Solar Cells via Fluorination of a Naphthalene Diimide-Based Copolymer Acceptor

Abstract

We investigate the photovoltaic properties and charge dynamics of all polymer solar cells (all-PSCs) based on poly­[(N,N′-bis­(2-octyl­dodecyl)­naphthalene-1,4,5,8-bis­(dicarboximide)-2,6-diyl)-alt-5,5′-(2,2′-bithiophene)] (P­(NDI2OD-T2)) and its fluorinated analogue, poly­[(N,N′-bis­(2-octyl­dodecyl)­naphthalene-1,4,5,8-bis­(dicarboximide)-2,6-diyl)-alt-5,5′-(3,3′-difluoro-2,2′-bithiophene)] (P­(NDI2OD-T2F)), as the acceptor polymer and poly­[4,8-bis­(5-(2-ethyl­hexyl)­thiophen-2-yl)­benzo­[1,2-b:4,5-b′]­dithiophene-alt-5-octyl-4H-thieno­[3,4-c]­pyrrole-4,6­(5H)-dione] (PBDTTTPD) as the donor polymer. The PBDTTTPD:P­(NDI2OD-T2)-based device has a high open-circuit voltage (V OC) of 1.03 V but suffers from low power conversion efficiency (PCE) of 2.02% with a short-circuit current density (J SC) and fill factor (FF) of 4.45 mA cm–2 and 0.44, respectively. In a stark contrast, the PCE of PBDTTTPD:P­(NDI2OD-T2F)-based PSC dramatically increases to 6.09% (V OC = 1.00 V, J SC = 11.68 mA cm–2, and FF = 0.52). These results are attributed to the fluorination, which removes the energetic barrier for hole transfer and promotes the formation of the donor/acceptor blend morphology with suppressed phase separation and enhanced intermixed phases. The detailed charge dynamics examined by femtosecond transient absorption spectroscopy suggests the significantly increased hole transfer efficiency and larger populations of long-lived polarons for PBDTTTPD:P­(NDI2OD-T2F).

Cyclometalated Pt complex based random terpolymers as electron acceptors for all polymer solar cells

“…As the electron‐withdrawing property of the Pt complex is weaker than the NDI moiety, therefore, the HOMO and LUMO rises with the introduction of Pt complex ratio in the terpolymers compared in PNDIT2 copolymers. And the HOMO and LUMO values for PNDIT2 measured in this work was in good agreement with literature reported values of −5.7 – −6.0 and −3.5 – −3.8 eV …”

Imide‐Functionalized Polymer Semiconductors

“…This same fluorinated polymer 31 a was also reported by Woo and co‐workers. When mixed with D11 , a PCE of 6.09 % was attained with a V oc of 1.00 V, J sc of 11.68 mA cm −2 , and FF of 52 % . F‐containing NDI‐based polymer 32 was synthesized by Ong et al.…”

“…When mixed with D11,aP CE of 6.09 %w as attainedw ith a V oc of 1.00 V, J sc of 11.68 mA cm À2 ,a nd FF of 52 %. [44] F-containing NDI-based polymer 32 was synthesized by Ong et al The resulting polymer showed ah igher absorptivity and increased intensityo fp-p stacking. The all-PSCs based on D1 as the donor polymer showed aP CE of 5.20 %.…”

8.0% Efficient All‐Polymer Solar Cells with High Photovoltage of 1.1 V and Internal Quantum Efficiency near Unity

“…The high-performance all-PSCs with PCEs over 7% only afford moderate V oc around 0.8 V, [18,22,24,26,28] whereas a few all-PSCs can emerge high V oc around 1.0 V, but the PCEs never surpass 7%. [20,[29][30][31][32] In contrast, a PC 71 BM-based PSC with a high V oc close to 1 V and a high PCE of 8.9% has been realized. [33] A nonfullerene PSC based on a polymer/small molecule blend also attained a high V oc of 1.12 V with a high PCE approaching 10%.…”

“…[15][16][17][18][19][20][21] However, the PCEs of the record all-PSCs are still behind those of the state-of-the-art PC 71 BM-based PSCs. [22][23][24][25][26] Among the high-performance all-PSCs to date, a relatively high short-circuit current density (J sc ) of 18.6 mA cm −2 , [27] or a high fill factor (FF) over 0.7 are achieved individually, [24,26,28] approaching to those of the record-efficiency PC 71 BM-based PSCs.…”