Raju Lampande

A highly efficient transition metal oxide layer for hole extraction and transport in inverted polymer bulk heterojunction solar cells

This paper demonstrates a comparative study of transition metal oxide materials, tungsten trioxide (WO3) and molybdenum trioxide (MoO3), as an effective hole extraction and transport layer in inverted polymer bulk heterojunction solar cells. Their device performances as an anode buffer layer are investigated based on thieno[3,4-b]thiophene/benzodithiophene (PTB7) and [6,6]-phenyl C70-butyric acid methyl ester(PC70BM) photoactive layers. The fabricated device with WO3 compared with MoO3 shows improved power conversion efficiency as high as 6.67% under a simulated AM1.5G illumination of 100 mW cm−2. The excellent performance of WO3 in inverted bulk heterojunction solar cells is attributed to an efficient hole extraction, excellent electron blocking capability, smooth morphology as well as better ohmic contact between the active layer and the metal electrode.

High-performance bipolar host materials for blue TADF devices with excellent external quantum efficiencies

New bipolar host molecules composed of carbazole, pyridoindole, and dibenzothiophene (DBT) were synthesized for blue thermally activated delayed fluorescence (TADF)-based organic light-emitting diodes (OLEDs). 2,8-Di(9H-carbazol-9-yl)dibenzo[b,d]thiophene, 9-(8-(9H-carbazol-9-yl)dibenzo[b,d]thiophen-2-yl)-9H-pyrido[2,3-b]indole, and 2,8-bis(9H-pyrido[2,3-b]indol-9-yl)dibenzo[b,d]thiophene were prepared based on the selective reactivity at the 2,8-positions of DBT. The new symmetric and asymmetric host materials exhibited high triplet energies (2.89–2.95 eV). 4,5-Di(9H-carbazol-9-yl)phthalonitrile (2CzPN) was selected as an emitting dopant for achieving sky-blue emissions in TADF-OLEDs. 2CzPN-doped TADF-OLEDs, whose configuration is ITO (50 nm)/HATCN (7 nm)/TAPC (75 nm)/host:6% 2CzPN (20 nm)/TmPyPB (50 nm)/LiF (15 nm)/Al (100 nm), showed low driving voltages and high external quantum efficiencies (EQEs). These results are attributed to the well-controlled bipolar character of the host giving a better charge balance in the emitting layer. In particular, the device containing ZDN:6% 2CzPN showed an unprecedentedly high EQE of 25.7% (at 0.074 mA cm−2).

New interfacial materials for rapid hole-extraction in organic photovoltaic cells

Two new hole-extraction materials, TPDI (5,10,15-triphenyl-5H-diindolo[3,2-a:3′,2′-c]carbazole) and TBDI (5,10,15-tribenzyl-5H-diindolo[3,2-a:3′,2′-c]carbazole), were synthesized and explored in planar heterojunction organic solar cells (OSCs). The synthesized materials have good transparency in the visible spectrum, high hole mobility, and compatible highest occupied molecular orbital (HOMO) values with the donor material, which make them excellent hole-extraction layers (HELs) for OSCs. The SubPc (subphthalocyanine chloride)/C60 and SubNc (subnaphthalocyanine chloride)/C60 OSCs with a TBDI HEL show impressive 35.9% and 29.1% improvements in power conversion efficiencies compared to reference devices. Their HOMO values were evaluated as 5.2–5.3 eV and hole mobilities were measured as 5.9–6.1 × 10−3 cm2 V−1 s−1 at 0.3 MV cm−1 by the space-charge limited current method.

New bipolar host materials for high performance of phosphorescent green organic light-emitting diodes

We report a series of four bipolar host materials with indenocarbozole and biphenyl pyrimidine moieties for efficient phosphorescent green organic light-emitting diodes (OLEDs). All four host materials possess excellent electro-optical properties as well as good thermal and morphological stability due to their high glass transition temperature of 129 °C and decomposition temperature of 363–401 °C. The new materials also show good triplet energy of 2.76 eV and excellent charge carrier transport properties. The fabricated OLED device with 11-[3-(2,6-diphenyl-pyrimidin-4-yl)-phenyl]-12,12-dimethyl-11,12-dihydro-11-aza-indeno[2,1-a]fluorene (mDPPICz1) as green host shows maximum current and power efficiency as high as 75.8 cd A−1 and 87.1 lm W−1 at 1000 cd m−2, and an almost ideal external quantum efficiency of 21.7%.

Effectiveness of a polyvinylpyrrolidone interlayer on a zinc oxide film for interfacial modification in inverted polymer solar cells

This paper investigate the effectiveness of non-conjugated polymer polyvinylpyrrolidone (PVP) at the interface of an n-type metal oxide buffer layer and the photoactive layer in inverted bulk heterojunction solar cells. A 15% enhancement in power conversion efficiency (PCE) is realized after the incorporation of a thin PVP layer between zinc oxide (ZnO) and polythieno[3,4-b]-thiophene-co-benzodithiophene (PTB7):[6,6]-phenyl C71-butyric acid methyl ester (PC70BM) based photoactive layer in inverted polymer solar cells. The fabricated devices with the PVP layer show enhanced PCE as high as 7.30% under simulated AM 1.5 G (100 mW cm−2) illumination. The ZnO/PVP improves the electron extraction property of the ITO electrode, effectively blocks holes from the highest occupied molecular orbital of the donor, suppresses charge recombination at the interface of ZnO and the photoactive layer, and decreases the interfacial contact resistance.

A new rigid diindolocarbazole donor moiety for high quantum efficiency thermally activated delayed fluorescence emitter

In this communication, we report an excellent new highly conjugated and rigid electron donor (diindolocarbazole) for thermally activated delayed fluorescence (TADF) emitters. The donor–acceptor structure with diindolocarbazole donor induces high oscillator strength as well as high probability for the radiative transition, suitable frontier molecular overlap with proper intramolecular charge transfer and a large dihedral angle with out-of-plane structure between electron donor and acceptor; this results in high photoluminescence quantum yield, small singlet–triplet energy splitting, and extremely short delayed fluorescence exciton lifetime. The fabricated organic light emitting diode with new donor applied green emitter exhibits a remarkably high external quantum efficiency of 31.4% without any out-coupling technique. It also shows extremely low efficiency roll-off characteristics with the highest luminance of 71 160 cd m−2 as well as good operational device stability.

A New Exciton Blocking Material for Organic Solar Cell Applications

We report a new efficient exciton blocking material, tris(2,4,6-trimethyl-3-(pyridin-3-l)phenyl) (3TPYMB), for organic solar cell applications. The introduction of 3TPYMB as an exciton blocking layer instead of well known BCP (2,9-dimethyl-4,7-diphenyl-1,10-phenanthroline) results in the significant improvement of short circuit current (Jsc) and open circuit voltage (Voc) in the boron subphthalocyanine (SubPC)/C60 based organic solar cell devices. As the results, the power conversion efficiency is enhanced by 11.8%. Such improvement with this new exciton blocking layer is mainly attributed to the good electron transportation by deep penetration of Al cathode metal to 3TPYMB layer.