Lal Mohammad

Benzothiadiazole-based polymer for single and double junction solar cells with high open circuit voltage.

Single and double junction solar cells with high open circuit voltage were fabricated using poly{thiophene-2,5-diyl-alt-[5,6-bis(dodecyloxy)benzo[c][1,2,5]thiadiazole]-4,7-diyl} (PBT-T1) blended with fullerene derivatives in different weight ratios. The role of fullerene loading on structural and morphological changes was investigated using atomic force microscopy (AFM) and X-ray diffraction (XRD). The XRD and AFM measurements showed that a higher fullerene mixing ratio led to breaking of inter-chain packing and hence resulted in smaller disordered polymer domains. When the PBT-T1:PC60BM weight ratio was 1 : 1, the polymer retained its structural order; however, large aggregated domains formed, leading to poor device performance due to low fill factor and short circuit current density. When the ratio was increased to 1 : 2 and then 1 : 3, smaller amorphous domains were observed, which improved photovoltaic performance. The 1 : 2 blending ratio was optimal due to adequate charge transport pathways giving rise to moderate short circuit current density and fill factor. Adding 1,8-diiodooctane (DIO) additive into the 1 : 2 blend films further improved both the short circuit current density and fill factor, leading to an increased efficiency to 4.5% with PC60BM and 5.65% with PC70BM. These single junction solar cells exhibited a high open circuit voltage at ∼ 0.9 V. Photo-charge extraction by linearly increasing voltage (Photo-CELIV) measurements showed the highest charge carrier mobility in the 1 : 2 film among the three ratios, which was further enhanced by introducing the DIO. The Photo-CELIV measurements with varying delay times showed significantly higher extracted charge carrier density for cells processed with DIO. Tandem devices using P3HT:IC60BA as bottom cell and PBT-T1:PC60BM as top cell exhibited a high open circuit voltage of 1.62 V with 5.2% power conversion efficiency.

Morphological Evolution and Its Impacts on Performance of Polymer Solar Cells

In this paper, the role of fullerene loading on the nanomorphology and photovoltaic performance of alternating copolymer poly{2-octyldodecyloxy-benzo[1,2-b;3,4-b] dithiophene-alt-5,6-bis(dodecyloxy)-4,7bis(thiophen-2-yl)-benzo[c] [1,2,5]-thiadiazole} (PBDT-ABT-1) blend films was investigated. The morphology of blend films with different Phenyl C-60-butyric acid methyl ester (PCBM) mixing ratios and solvent additives was studied using atomic force microscopy (AFM) and energy-filtered transmission electron microscopy (EFTEM). AFM and EFTEM images showed difference in the intermixing of polymer with fullerene between 1:1, 1:2, and 1:3 weight ratios. Polymer/PCBM intermixed domain size increases with higher PCBM weight ratios. X-ray diffraction measurements on the pristine polymer and blend films cast without additives did not show any peaks, suggesting an amorphous nature of PBDT-ABT-1. EFTEM images from the donor/acceptor composite showed intermixed polymer-PCBM domains separated by the polymer boundary. Furthermore, EFTEM images for di-iodooctane (DIO) additive cast film revealed purer polymer domain. Photo-charge extraction by linearly increasing voltage measurement exhibited that charge extraction is highest in the nanomorphology sample with a weight ratio of 1:2, corresponding to the lowest bimolecular recombination and the highest charge carrier mobility.

Optimization of Interconnecting Layers for Double- and Triple-Junction Polymer Solar Cells

In solution-processed tandem polymer solar cells, one of the most challenging parts is the optimization of interconnecting layers (ICLs) between subcells. In this study, ICLs were optimized for double- and triple-junction polymer solar cells. We investigated the robustness of PEDOT:PSS/AZO/PEIE ICL for tandem polymer solar cells. Solvent testing for ICL robustness showed a uniform coverage of the PEDOT:PSS layer when prepared without adding DMSO and IPA in PEDOT:PSS and with no use of additional filters. The performance of tandem polymer solar cells was investigated on different temperatures of interfacial layer. The PEDOT:PSS annealing temperature can be used from 120°C to 130°C, while aluminum-doped zinc oxide (AZO) temperature can be used from 120°C to 150°C. Lowering the annealing temperature in ICLs might help to fabricate triple-junction solar cells because they require more layers, and some low-bandgap polymers cannot sustain high temperature. However, reduction in annealing temperature in PEDOT:PSS, AZO, and PEIE led to lower FF and Jsc. A double-junction device Voc of 1.05 V and a triple-junction Voc of 1.4 V indicated that the ICLs worked effectively.

Shelf life stability comparison in air for solution processed pristine PDPP3T polymer and doped spiro-OMeTAD as hole transport layer for perovskite solar cell

This data in brief includes forward and reverse scanned current density–voltage (J–V) characteristics of perovskite solar cells with PDPP3T and spiro-OMeTAD as HTL, stability testing conditions of perovskite solar cell shelf life in air for both PDPP3T and spiro-OMeTAD as HTL as per the description in Ref. [1], and individual J–V performance parameters acquired with increasing time exposed in ambient air are shown for both type of devices using PDPP3T and spiro-OMeTAD as HTL. The data collected in this study compares the device stability with time for both PDPP3T and spiro-OMeTAD based perovskite solar cells and is directly related to our research article “solution processed pristine PDPP3T polymer as hole transport layer for efficient perovskite solar cells with slower degradation” [2].

Influence of Nanoscale Morphology on Performance of Inverted Structure Metallated Conjugated Polymer Solar Cells

Inverted polymer solar cells (iPSCs) have shown a great potential in organic photovoltaics due to its enhanced stability and large-scale roll-to-roll processing. Metallated conjugated polymers also show promise as a donor material in the PSCs. In this paper, the role of solvents on the performance of inverted structure metallated PSCs was understood. Chlorobenzene (CB) and toluene were used as solvents to obtain the optimum morphology for improved device efficiency. To understand the charge transport properties and charge carrier lifetime in metallated polymer iPSCs, atomic force microscopy and transient photocurrent measurements were performed. The results showed that the CB as a solvent can improve the morphology of the active layer and enhance the performance of metallated iPSCs.

Efficient CsF interlayer for high and low bandgap polymer solar cell

Low bandgap polymer solar cells have a great deal of importance in flexible photovoltaic market to absorb sun light more efficiently. Efficient wide bandgap solar cells are always available in nature to absorb visible photons. The development and incorporation of infrared photovoltaics (IR PV) with wide bandgap solar cells can improve overall solar device performance. Here, we have developed an efficient low bandgap polymer solar cell with CsF as interfacial layer in regular structure. Polymer solar cell devices with CsF shows enhanced performance than Ca as interfacial layer. The power conversion efficiency of 4.5% has been obtained for PDPP3T based polymer solar cell with CsF as interlayer. Finally, an optimal thickness with CsF as interfacial layer has been found to improve the efficiency in low bandgap polymer solar cells.

Investigation of device performance due to inclusion of Ru and Pt based heavy metals in organometllic solar cells

Conjugated polymers doped with metal ions offer superior material properties in the development of next generation flexible PV technology [1]. Charge transport mechanism in metallated conjugated polymer with different solvent processing was described by A.F. Mitul in [1]. In this work, the modification of heavy metals e.g, Pt, Ru etc in organometllic solar devices are investigated. The variation in device performance i.e, open circuit voltage (Voc), external quantum efficiency (EQE) is explained in the light of nano scale morphology. Change of heavy metals in organicchemical structure provides differences in nanoscale morphology and hence, it describes the favorable condition for optimum device performance.

Optimization of interfacial layer for double and triple junction polymer solar cell

Solution processed tandem polymer solar cell has drawn a great deal of attention due its low cost, ease of production and capability of harvesting solar energy more efficiently. In solution processed tandem polymer solar cell, the most challenging part is the optimization of interfacial layer. In this work, we have investigated the robustness of PEDOT:PSS/AZO/PEIE interfacial layer to develop tandem polymer solar cell. While developing triple junction polymer solar cell, temperature of second interfacial layer has also a great impact on overall device performance. Here, the performance of tandem polymer solar cell was investigated on different temperature of interfacial layer.