A generic green solvent concept boosting the power conversion efficiency of all-polymer solar cells to 11%

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1 Electronic Supplementry Mteril (ESI) for Energy & Environmentl Science. This journl is The Royl Society of Chemistry 28 Electronic Supporting Informtion A generic green solvent concept boosting the power conversion efficiency of ll-polymer solr cells to % Zhenye Li, Lei Ying*, Peng Zhu, Wenki Zhong, Ning Li* b, Feng Liu c, Fei Hung*, nd Yong Co Institute of Polymer Optoelectronic Mterils nd Devices, Stte Key Lbortory of Luminescent Mterils nd Devices, South Chin University of Technology, Gungzhou, 564, P. R. Chin. E-mil: msleiying@scut.edu.cn; msfhung@scut.edu.cn b Institute of Mterils for Electronics nd Energy Technology (i-meet), FAU Erlngen- Nürnberg, 958 Erlngen, Germny. E-mil: ning.li@fu.de c Deprtment of Physics nd Astronomy Shnghi Jio Tong University, Shnghi 224, P. R. Chin Experimentl Section Mterils PTzBI-Si nd N22 were synthesised ccording to procedures reported in the literture. 2- MeTHF, THF, CPME nd DBE re purchsed from Sigm-Aldrich without further purifiction. Fbriction of Polymer Solr Cells Indium tin oxide (ITO)-coted glss substrtes were successively clened by soniction in detergent, deionised wter, cetone, nd isopropyl lcohol nd dried in n oven t 75 C for 6

2 h prior to use. The substrtes were then exposed to oxygen plsm for min nd spin coted with PEDOT:PSS (Clevios P VP Al 483) t 3 rpm for 3 s. The coted substrtes were nneled t 5 C on hot plte for 2 min in ir to produce 4-nm thin films. After nneling, they were trnsferred to glove box under N2 tmosphere. For 2-MeTHF processed ll-pscs, the totl concentrtion of PTzBI-Si nd N22 ws fixed t 6 mg ml, nd the blend films were obtined by spin coting solutions of the polymers in MeTHF contining DBE (.5 vol %); to obtin ctive lyer of PTzBI-Si:N22 with higher thicknesses of 3, 6, 23, nd 35 nm, we kept higher constnt totl concentrtion of PTzBI-Si nd N22 of 6 mg ml - nd employed vried rotting speed of 3, 8,, nd 6 rpm, respectively. For THF processed ll-pscs, the totl concentrtion of PTzBI-Si nd N22 ws fixed t 2 mg ml, nd the blend films were obtined by spin coting solutions of the polymers in THF contining DBE (.5 vol %); to obtin ctive lyer of PTzBI-Si:N22 with higher thicknesses of 3, 6, 23, nd 35 nm, we kept higher constnt totl concentrtion of PTzBI-Si nd N22 of 2 mg ml - nd employed vried rotting speed of 4, 25,, nd 6 rpm, respectively. For CPME processed ll-pscs, the totl concentrtion of PTzBI-Si nd N22 ws fixed t 9 mg ml, nd the blend films were obtined by spin coting solutions of the polymers in CPME contining DBE (.5 vol %); to obtin ctive lyer of PTzBI-Si:N22 with higher thicknesses of 3, 6, 23, nd 35 nm, we kept higher constnt totl concentrtion of PTzBI-Si nd N22 of 9 mg ml - nd employed vried rotting speed of 3, 2, 2, nd 6 rpm, respectively. For CB processed ll-pscs, the totl concentrtion of PTzBI-Si nd N22 ws fixed t.5 mg ml, nd fter spin-coting the solution t 7 rpm for 9 s, the robust film with thickness of bout 3 nm ws obtined. For DCB processed ll-pscs, the totl concentrtion of PTzBI-Si nd N22 ws fixed t 3 mg ml, nd fter spin-coting the solution t 7 rpm for 2 s, the robust film with thickness of bout 3 nm ws obtined. For CF processed ll-pscs, the totl concentrtion of PTzBI-Si nd N22 ws fixed t 7.5 mg ml, nd fter spin-coting 2

3 the solution t 9 rpm for 3 s, the robust film with thickness of bout 3 nm ws obtined. The photoctive lyers were then thermlly nneled t C for min, followed by spin coting of 5-nm lyer of PFNDI-Br t 2 rpm for 3 s to serve s the cthode interfce. A -nm rgentum (Ag) lyer ws then thermlly deposited onto the ctive lyer through shdow msk in vcuum chmber with bse pressure of 2 6 mbr. The effective re of the devices (.4 cm 2 ) ws determined by the shdow msk. Fbriction nd Chrcteristion of Chrge-Only Devices The hole mobility ws mesured in hole-only device with the configurtion of ITO/PEDOT:PSS/ctive lyer/ag. The electron mobility ws mesured in n electron-only device with the configurtion of ITO/ZnO/ctive lyer/pfndi-br/ag. The ZnO sol-gel is obtined from stirring the solution of. g Zn(CH3COO)2 2H2O in ml ethylene glycol monomethyl ether nd 275 μl ethylenedimine t 6 o C for 2 h. For 2-MeTHF processed ll-pscs, the totl concentrtion of PTzBI-Si nd N22 ws fixed t 6 mg ml, nd the blend films were obtined by spin coting solutions of the polymers in MeTHF contining DBE (.5 vol %); to obtin ctive lyer of PTzBI-Si:N22 with higher thicknesses of 3, 6, 23, nd 35 nm, we kept higher constnt totl concentrtion of PTzBI-Si nd N22 of 6 mg ml - nd employed vried rotting speed of 3, 8,, nd 6 rpm, respectively. For THF processed ll-pscs, the totl concentrtion of PTzBI-Si nd N22 ws fixed t 2 mg ml, nd the blend films were obtined by spin coting solutions of the polymers in THF contining DBE (.5 vol %); to obtin ctive lyer of PTzBI-Si:N22 with higher thicknesses of 3, 6, 23, nd 35 nm, we kept higher constnt totl concentrtion of PTzBI-Si nd N22 of 2 mg ml - nd employed vried rotting speed of 4, 25,, nd 6 rpm, respectively. For CPME processed ll-pscs, the totl concentrtion of PTzBI-Si nd N22 ws fixed t 9 mg ml, nd the blend films were obtined by spin coting solutions of the polymers in CPME contining DBE (.5 vol %); to 3

4 obtin ctive lyer of PTzBI-Si:N22 with higher thicknesses of 3, 6, 23, nd 35 nm, we kept higher constnt totl concentrtion of PTzBI-Si nd N22 of 9 mg ml - nd employed vried rotting speed of 3, 2, 2, nd 6 rpm, respectively. The mobility μ ws determined by fitting the drk current to the model of single-crrier SCLC, which is described by Eqution (): J= (9/8)εεrμVeff 2 /d 3, () where J is the current density, μ is the chrge (hole or electron) mobility t zero field, ε is the permittivity of free spce, εr is the reltive permittivity of the mteril, d is the thickness of the ctive lyer, nd Veff is the effective voltge (V Vbi). The chrge (hole or electron) mobility ws clculted from the y intercept of the J V curves. Instruments nd Chrcteristion The bsorption spectr of the film nd solution smples were mesured using UV vis spectrophotometer (HP 8453, photodiode rry type) in the wvelength rnge of 3 nm. PL spectr were recorded on Jobin-Yvon FluoroMx-4 spectrofluorometer. The current density voltge (J V) chrcteristics were mesured using computer-controlled Keithley 24 SourceMeter under sun irrdition from n AM.5 G solr simultor (Tiwn, Enlitech, SS-F5). The EQE spectr were mesured using commercil EQE system (Tiwn, Enlitech, QE-R3). Grzing incidence wide-ngle X-ry scttering (GIWAXS) GIWAXS chrcteriztion of the thin films ws performed t bemline of Advnced Light Source, Lwrence Berkeley Ntionl Lbortory (LBNL). The X-ry bem energy ws kev. The smple to detector distnce ws ~28 mm clibrted with AgB nd the incidence ngle ws.6o normlized by photodiode. All the GIWAXS signls were recorded in Helium tmosphere with exposure time of 5 s per imge using 2D chrge-coupled device 4

5 (CCD) detector (Piltus 2M) with pixel size of.72 mm by.72 mm. Thin film smples were spin-coted on PEDOT:PSS/silicon wfer substrtes. Resonnt soft X-ry scttering (R-SoXS) RSoXS ws performed t bemline...2 of Advnced Light Source, LBNL. Smple preprtion ws the sme s tht of GIWAXS smples. The thin films were floted in deionized wter nd trnsferred on silicon nitrile (Si3N4) windows, nd subsequently the smples were loded onto holder. After the films were dried in ir, the holder ws trnsferred into the vcuum chmber for RSoXS. The bem energy ws screened rnging from 28 to 29 ev, with s exposure time per energy. The scttering ptterns were collected in vcuum using Princeton Instrument PI-MTE CCD cmer with pixel size of.27 mm by.27 mm. RSoXS dt of ech smple were recorded t two smple-to-ccd distnce of 5 nd 5 mm. Tble S. Polymer solubility test t different tempertures with certin concentrtions in CPME. Totl Conc. Solubility Solubility Solubility Polymer (mg ml - ) (2 o C) (6 o C) (R.T. 25 o C) PTzBI-Si N c + c PTzBI-Si:N22 (:.5) c +++ represents good solubility, ++ represents soluble but with high viscosity, + represents forming nerly gel stte; 2 c stirred t 2 o C for 3 min nd then cooled down to 6 o C or R.T. 5

6 Tble S2. Photovoltic prmeters of ll-pscs with the ctive lyers processed by vrious solvent nd solvent dditives. Solvent Solvent dditive V OC (V) J SC FF PCE 2-MeTHF N/A % DBE % DPE THF N/A % DBE % DPE CPME N/A % DBE % DBE CB N/A DCB N/A CF N/A Tble S3. Photovoltic prmeters of ll-pscs therml nnel (TA) for min t different temperture. Solvent Therml nneling V OC (V) J SC FF PCE 2-MeTHF /min /min /min THF /min /min /min CPME /min /min With.5vol%DBE. 2 /min

7 (). treted with 8 o C in the glovebox (b). illuminted under sun irrdition in the glovebox Norm. PCE MeTHF THF CPME Norm. PCE MeTHF THF CPME Time (h) Time (h) Fig. S. Normlized PCE of 2-MeTHF, THF nd CPME processed ll-pscs blend films treted with 8 o C () nd illuminted under sun irrdition in the glovebox for different time. Tble S4. Photovoltic prmeters of 2-MeTHF processed ll-pscs with different thickness. Solvent Thickness (nm) V OC (V) J SC FF PCE 2-MeTHF With.5vol%DBE

8 Integrted J SC () Current density MeTHF processed device 3nm 23nm 35nm (b) EQE nm 23nm 35nm Voltge (V) Wvelength (nm) Fig. S2. () J-V chrcteristics nd (b) EQE spectr of 2-MeTHF processed ll-pscs with different thickness. Tble S5. Photovoltic prmeters of THF processed ll-pscs with different thickness. Solvent Thickness (nm) V OC (V) J SC FF PCE THF With.5vol%DBE. 8

9 Integrted J SC () Current density THF processed device 3nm 23nm 35nm (b) EQE nm 23nm 35nm Voltge (V) Wvelength (nm) Fig. S3. () J-V chrcteristics nd (b) EQE spectr of THF processed ll-pscs with different thickness. Tble S6. Photovoltic prmeters of CPME processed ll-pscs with different thickness. Solvent Thickness (nm) V OC (V) J SC FF PCE CPME With.5vol%DBE

10 Integrted J SC () Current density CPME processed device 3nm 23nm 35nm (b) EQE nm 23nm 35nm Voltge (V) Wvelength (nm) Fig. S4. () J-V chrcteristics nd (b) EQE spectr of CPME processed ll-pscs with different thickness. ().5 ~5nm ~22nm ~3nm ~4nm net PTzBI-Si hole-only device (b).5 ~5nm ~22nm ~3nm ~36nm net N22 electron-only device J /2 (A /2 /cm) J /2 (A /2 /cm).5.5 (c) Hole mobility (x -2 cm 2 V - s - ) V -V -V (V) ppl bi s 2.5 PTzBI-Si Thickness (nm) (d) Electron mobility (x -3 cm 2 V - s - ) V -V -V (V) ppl bi s 3 N Thickness (nm) Fig. S5. SCLC hole nd electron mobility for PTzBI-Si () nd N22 (b); hole mobility nd electron mobility versus thickness chrcteristics for PTzBI-Si (c) nd N22 (d).

11 Tble S7. SCLC electron (hole) mobility mesurements for PTzBI-Si nd N22 with different thickness. Polymer μ h (cm 2 V - s - ) μ e (cm 2 V - s - ) Thickness (nm) PTzBI-Si / ~ / ~ / ~ / ~4 N22 /.98-3 ~5 / ~22 / ~3 / ~36 All of the blend films re treted with o C for min. () ~3nm ~6nm ~23nm ~34nm 2-MeTHF processed (b) ~3nm ~6nm ~23nm ~34nm THF processed (c) 2.5 ~3nm ~6nm ~23nm ~34nm CPME processed J /2 (A /2 /cm).2.8 hole-only device J /2 (A /2 /cm).2.8 hole-only device J /2 (A /2 /cm) hole-only device (d) J /2 (A /2 /cm) V -V -V (V) ppl bi s ~3nm ~6nm ~23nm ~34nm electron-only device 2-MeTHF processed (e) J /2 (A /2 /cm) V -V -V (V) ppl bi s.5.5 ~3nm ~6nm ~23nm ~34nm electron-only device THF processed (f) J /2 (A /2 /cm) V -V -V (V) ppl bi s ~3nm ~6nm ~23nm ~34nm electron-only device CPME processed V -V -V (V) ppl bi s V -V -V (V) ppl bi s V -V -V (V) ppl bi s Fig. S6. SCLC hole nd electron mobility for 2-MeTHF (, d), THF (b, e) nd CPME (c, f) processed devices with different thickness.

12 Tble S8. SCLC electron (hole) mobility mesurements for 2-MeTHF, THF nd CPME processed devices with different thickness. Solvent μ h (cm 2 V - s - ) μ e (cm 2 V - s - ) μ h /μ e Thickness (nm) 2-MeTHF ~ ~ ~ ~34 THF ~ ~ ~ ~34 CPME ~ ~ ~ ~34 All of the blend films re treted with o C for min. Chrge genertion, recombintion nd extrction To investigte the photoinduced crrier genertion nd chrge collection behvior of 2- MeTHF, THF nd CPME processed ll-pscs, we plotted the dependence of the photocurrent density (Jph) on the effective voltge (Veff) under illumintion t mw cm 2 on doublelogrithmic scle (Fig. S7). The photocurrent density (Jph) is defined by Jph = JL JD, where JL nd JD stnd for the current densities mesured under illumintion nd in the drk, respectively. The effective voltge (Veff) is defined s Veff = Vbi Vppl, where Vbi is the voltge when Jph = (the built-in voltge) nd Vppl is the pplied voltge. 3,4 As depicted in Fig. S7, 2

13 Jph incresed linerly when Veff ws below.2 V nd tended to sturte t sufficiently high Veff bove 2 V, suggesting tht sweep out ll of the generted crriers to the electrodes t n effective voltge bove 2 V. Therefore, the mximum photoinduced crrier genertion rte Gmx cn be clculted from the eqution Gmx = Jst/(q L), where q is the elementry chrge nd L is the ctive-lyer thickness, nd the chrge collection cpcity PC cn be clculted using the eqution PC = Jph/Jst. As shown in Tble S9 (in the ESI), the CPME processed ll- PSCs simultneously exhibited the highest vlues of Gmx ( m 3 s ) nd PC (.986), indicting tht the device possessed good crrier genertion nd collection bility nd thus high JSC vlues. The chrge trnsfer properties of 2-MeTHF, THF nd CPME processed ll-pscs were exmined by mesuring the photoluminescence (PL) spectr of PTzBI-Si:N22 blend films excited t both 55 nd 74 nm. 5 The PL emissions from PTzBI-Si (excited t 55 nm) nd N22 (excited t 74 nm) were quenched more completely in the CPME processed ll-pscs thn tht in the 2-MeTHF nd THF processed ll-pscs (Fig. S7b), indicting the more effective chrge crrier dissocition of the generted excitons in this device. Due to the limited exciton diffusion length, efficient PL quenching in the CPME processed ll-pscs lso implies tht donor (PTzBI-Si) nd cceptor polymers (N22) re mixed on the sub- nm length scle. 6 The JSC versus light intensity (Plight) chrcteristics were mesured for 2- MeTHF, THF nd CPME processed ll-pscs to investigte the chrge recombintion dynmics in the photoctive lyer, nd the relevnt plots nd prmeters re shown in Fig. S7c. For orgnic solr cells, it is well estblished tht the power-lw dependence of JSC on the illumintion intensity cn generlly be expressed s JSC (Plight) S, where Plight is the light intensity nd S is the exponentil fctor, which is close to unity when bimoleculr recombintion is wek in the device. 7,8 The extrcted S vlue ws.99 for CPME processed ll-pscs (while.94 nd.9 for 2-MeTHF nd THF processed ll-pscs, respectively), suggesting tht the bimoleculr recombintion ws weker in CPME processed ll-pscs thn 3

14 tht in 2-MeTHF nd THF processed ll-pscs. This observtion ws consistent with the high FF vlues (>77%) of the corresponding ll-pscs. It is well known tht the VOC depends on the nturl logrithm of Plight provided the slope vlue with units of kt/q, where k is the Boltzmnn constnt, T is temperture, nd q is the elementry chrge. A slope of kt/q is expected for bimoleculr recombintion, wheres strong dependence of VOC on the light intensity (2kT/q) is chrcteristic of monomoleculr or trp-ssisted recombintion. 9 As shown in Fig. S7d, the observed slopes of the 2-MeTHF, THF nd CPME processed ll-pscs were.46,.64 nd.39 kt/q, respectively, indicting tht the other recombintion mechnisms (except for bimoleculr recombintion) such s monomoleculr or trp-ssisted recombintion re effectively suppressed in CPME processed ll-pscs. The FF Plight chrcteristics re plotted in Fig. S7e. In the low-plight regime, the CPME processed ll-pscs exhibited higher FF thn 2-MeTHF nd THF processed ll-pscs, indicting weker bimoleculr recombintion in this device. Fig. S7f shows the drk J V curves for 2-MeTHF, THF nd CPME processed ll-pscs. Fitting the drk J V curves by one-diode equivlent circuit, the diode idelity fctor n ws clculted to be.74,.79 nd.67 for 2-MeTHF, THF nd CPME processed ll-pscs, respectively. The lower idelity fctor of CPME processed ll-pscs is considered to originte from weker recombintion induced by defect sttes. Moreover, ccording to the J V chrcteristics mesured in the drk (Tble S, ESI), the CPME processed ll-pscs exhibited much lower series resistnce (Rs =. Ω cm 2 ) nd comprbly high prllel device resistnce (Rp = Ω cm 2 ) thn those of 2-MeTHF (Rs = 2.37 Ω cm 2 nd Rp = Ω cm 2 ) nd THF (Rs = 2.44 Ω cm 2 nd Rp = Ω cm 2 ) processed ll-pscs. We lso clculted the FF including the series nd prllel resistnce losses (FFSP) using the equivlent circuit model,,2 nd obtined vlues were 7.6%, 64.4% nd 76.2% for 2- MeTHF, THF nd CPME processed ll-pscs, respectively (Tble S, ESI). These clculted FF vlues re in good greement with tht obtined from the J V plots. 4

15 () (b) 2x 6 (c) J ph 2-MeTHF THF CPME.. V (V) eff (d) (e) (f) V OC (V) MeTHF (.46 kt/q) THF (.64 kt/q) CPME (.39 kt/q) PL intensity (.u.).5x 6 Fill fctor x 6 5x MeTHF@55nm THF@55nm CPME@55nm PL intensity (.u.) 2-MeTHF THF CPME 2-MeTHF@74nm THF@74nm CPME@74nm Wvelength (nm) Wvelength (nm) J SC Current density MeTHF (S=.94) THF (S=.9) CPME (S=.99) Light intensity (mw cm -2 ) 2-MeTHF (n=.74) THF (n=.79) CPME (n=.67) Light intensity (mw cm -2 ) 4 Light intensity (mw cm -2 ) Voltge (V) Fig. S7. () Jph Veff curves, (b) PL spectr, (c-e) JSC, VOC nd FF versus light intensity (Plight) chrcteristics, (f) drk J V curves nd corresponding idelity fctors (fitted by one-diode equivlent circuit) for 2-MeTHF, THF nd CPME processed ll-pscs. Tble S9. Relevnt prmeters obtined from Jph Veff curves. Solvent J ph b J st G mx (m -3 s - ) PC b L (nm) 2-MeTHF ~3 THF ~3 CPME ~3 All of the blend films treted with o C for min ; b At the condition of Veff = V - Vppl (Vppl =, under short-circuit condition). 5

16 Tble S. Series resistnce (RS), shunt resistnce (RP), nd the simulted idelity fctor n for 2-MeTHF, THF nd CPME processed devices obtined from drk J V chrcteristics. Device RS (Ω cm -2 ) RP (Ω cm -2 ) n 2-MeTHF THF CPME RS nd RP were were clculted round 2 V nd V, respectively, from the drk J V chrcteristics. b n ws estimted by fitting of one diode replcement circuit for the drk J V chrcteristics. Tble S. Clculted photovoltic prmeters for 2-MeTHF, THF nd CPME processed devices. Device v oc b R S * (Ω cm -2 ) R P * (Ω cm -2 ) r s b r p b FF b FF S b FF SP b 2-MeTHF THF CPME RS * nd RP * were obtined from illuminted J V chrcteristics. b According to n equivlent circuit model reported by Kippelen et l., the upper-limit fill fctor (FF), Rs-onlyinfluenced fill fctor (FFS), nd both Rs- nd Rp-influenced fill fctor (FFSP ) cn be clculted s follows, FF = [voc ln(voc +.72)]/(voc+), (RS = /RP = ) FFS = FF (. rs) +.9 rs 2, ( rs.4, / rp = ) FFSP = FFS [ (voc +.7)*FFS /(voc* rp)], ( rs +/ rp.4) 6

17 Where voc = qvoc/nkt, q is the elementry chrge, n is the idelity fctor of the diode, nd k is the Boltzmnn s constnt. rs nd rp re normlized series nd shunt resistnce (rs = RS *JSC/VOC, rp = RP* JSC/VOC). () PTzBI-Si (c) in-plne out-of-plne (b) N22 Fig. S8. GIWAXS ptterns of net PTzBI-Si () nd N22 (b) films; one-dimensionl integrted scttering profiles for the corresponding films (c). 7

18 () (b) (c) x -6 x -6 x x -3 2 Fig. S9. Fitting results nd TSI of I(q)q 2 [.u.] versus to q [Å ] RSoXS profiles of blend films processed with THF, 2-MeTHF, nd CPME. 25 x -6 x -6 THF TSI = 6.653e-6.u. x x -6 x -6 2-MeTHF TSI = e-6.u. 5 x x CPME TSI = e-6.u. 5 x Tble S2. Photovoltic prmeters of ll-pscs mesured under AM.5 Illumintion t mw/cm 2. D:A PTB7- Th:N22 ) Solvent V OC (V) J SC d) J SC, EQE e) FF PCE vg f) PCE mx 2-MeTHF.8 4.6± ±.8 5.9±.2 6. THF.8 3.5± ±.6 5.2± CPME.8 4.8± ±.7 6.8± J5:N22 b) THF.82 4.± ±.8 6.9± MeTHF ± ±.9 7.5± PTzBI:N22 c) CPME ± ±.5 8.4± MeTHF ± ±.5 8.9±.2 9. THF.84.9± ±.8 6.5± CPME.84 6.± ±.7 9.7± ) PTB7-Th:N22 = 2: (wt:wt) without therml nneling (TA). b) J5:N22 = 2: (wt:wt) treted with o C for min. c) PTzBI:N22 = 2: (wt:wt) treted with 3 o C for min. d) Obtined from J V mesurements. e) Obtined from the integrtion of EQE spectr. f) The PCE vlues re obtined from 2 seprte devices. 8

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