Despite being the most commonly used hole transport layer for p-i-n perovskite solar cells, the conventional PEDOT:PSS layer is far from being optimal for the best photovoltaic performance. Herein, we demonstrate highly conductive thin DMSO-doped PEDOT:PSS layers which significantly enhance the light harvesting, charge extraction, and photocurrent production of organo-lead iodide devices. Both imaging and X-ray analysis reveal that the perovskite thin films grown on DMSO-doped PEDOT:PSS exhibit larger grains with increased crystallinity. Altogether, these improvements result in a 37% boost in the power conversion efficiency (PCE) compared to standard p-i-n photovoltaics with pristine PEDOT:PSS. Furthermore, we demonstrate that DMSO-doped PEDOT:PSS devices possess enhanced PCE durability over time which we attribute primarily to fill factor stability.

In this work, a 9.5% of power conversion efficiency (PCE) is obtained in the thieno [3,4‐b] thiophene/benzodithiophene (PTB7): (6,6)‐phenyl‐C70‐butyric acid methyl ester (PC70BM) based polymer solar cell (PSC) by using a novel binary solvent additive of diphenyl ether (DPE): 1,8‐diiodoctane (DIO). We find that this binary solvent additive approach increases the PTB7 donor crystallinity using DPE and enhances the PC70BM dispersion using DIO. This amended aggregation results in a better donor/acceptor phase separation. We show that the improved crystallization and face‐on orientation preference of PTB7 contributes to higher light absorption and charge transport efficiency in the active layer. Moreover, a better D/A phase separation provides more efficient charge extraction and suppresses the charge recombination, leading to an improved FF >70%.

The p-i-n structure for perovskite solar cells has recently shown significant advantages in minimal hysteresis effects, and scalable manufacturing potential using low-temperature solution processing. However, the power conversion efficiency (PCE) of the perovskite p-i-n structure remains low mainly due to limitations using a flat electron transport layer (ETL). In this work, we demonstrate a new approach using spray coating to fabricate the [6,6]-phenyl-C(61)-butyric acid methyl ester (PCBM) ETL. By creating a rough surface, we effectively improve the light trapping properties inside the PCBM ETL. We reveal that the spray coated PCBM can form a cross-linked network, which may facilitate better charge transport and enhance extraction efficiency. By improving the contact between the perovskite film and the PCBM ETL, a reduction in the trap states is observed resulting in a PCE increase from 13% to >17%.

Organic photovoltaics (OPVs) were fabricated with blended active layers of poly[[4,8-bis[(2-ethylhexyl)oxy]benzo[1,2-b:4,5-b']dithiophene-2,6-diyl][3-fluoro-2-[(2-ethylhexyl)carbonyl]thieno[3,4-b]thiophenediyl]]:[6,6]-phenylC71-butyric acid methyl ester (PTB7:PC71BM). The active layers were prepared in chlorobenzene (CB) with different additives of 1,8-diiodooctane (DIO) and 1,8-dibromooctane and different concentrations using a wet process with spin coating. The effects of different solvent additives were studied with respect to photovoltaic parameters such as fill factor, short circuit current density, and power conversion efficiency. The absorption and surface morphology of the active layers were investigated by UV-visible spectroscopy, atomic force microscopy (AFM) and time-of-flight secondary ion mass spectrometry (TOF-SIMS), respectively. The results indicated that structural and morphological changes were induced by the solvent additives. The polymer solar cells (PSCs) of PTB7/PC71BM prepared by a spin coating method using DIO and 1,8-dibromooctane showed more improved PCE of 6.76%. The enhancement of performance of PSCs could be mainly attributed to the absorption enhancement and the improved charge carrier transportation.

Alternative low-temperature solution-processed hole-transporting materials (HTMs) without dopant are critical for highly efficient perovskite solar cells (PSCs). Here, two novel small molecule HTMs with linear π-conjugated structure, 4,4'-bis(4-(di-p-toyl)aminostyryl)biphenyl (TPASBP) and 1,4'-bis(4-(di-p-toyl)aminostyryl)benzene (TPASB), are applied as hole-transporting layer (HTL) by low-temperature (sub-100 °C) solution-processed method in p-i-n PSCs. Compared with standard poly(3,4-ethylenedioxythiophene): poly(styrenesulfonic acid) (PEDOT:PSS) HTL, both TPASBP and TPASB HTLs can promote the growth of perovskite (CH NH PbI ) film consisting of large grains and less grain boundaries. Furthermore, the hole extraction at HTL/CH NH PbI interface and the hole transport in HTL are also more efficient under the conditions of using TPASBP or TPASB as HTL. Hence, the photovoltaic performance of the PSCs is dramatically enhanced, leading to the high efficiencies of 17.4% and 17.6% for the PSCs using TPASBP and TPASB as HTL, respectively, which are ≈40% higher than that of the standard PSC using PEDOT:PSS HTL.

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The impact of two kinds of additives, such as 1,8-octanedithiol (ODT), 1,8-diiodooctane (DIO), diphenylether (DPE), and 1-chloronaphthalene (CN), on the performance of poly[(5,6-difluoro-2,1,3-benzothiadiazol-4,7-diyl)-alt-(3,3‴-di(2-octyldodecyl)2,2';5',2″;5″,2‴-quaterthiophen-5,5‴-diyl)] (PffBT4T-2OD):[6,6]-phenyl-C71-butyric acid methyl ester (PC71BM) based polymer solar cell are investigated. The polymer solar cells (PSCs) of PffBT4T-2OD:PC71BM by using CN show a more improved PCE of 10.23%. The solubility difference of PffBT4T-2OD in DIO and CN creates the fine transformation in phase separation and favorable nanoscale morphology. Grazing incidence X-ray diffraction (GIXRD) data clearly shows molecular stacking and orientation of the active layer. Interestingly, DIO and CN have different functions on the effect of the molecular orientation. These interesting studies provide important guidance to optimize and control complicated molecular orientations and nanoscale morphology of PffBT4T-2OD based thick films for the application in PSCs.

Improvement of the interface between the perovskite layer and the electron‐transport layer (ETL) is critical toward the advancement of planar perovskite solar cells (PSCs). It is important to obtain a uniform and pinhole‐free ETL that can minimize film defects and thus undesirable electron–hole recombination between the perovskite layer and cathode. However, this is extremely difficult because the rough perovskite surface causes charge–carrier recombination, facilitates large leakage currents, and inevitably deteriorates the electron‐extraction efficiency. Here, fluorine‐containing insulating polymers, poly(perfluorobutenylvinylether) (Cytop), are used as the tunneling layer in planar PSCs for the first time, resulting in a significant improvement in the power conversion efficiency (PCE) from 11.9% to over 14.5%. It is found that the Cytop layer not only fills the pinholes of the perovskite surface to decrease the trap concentration, but can also provide a strong electron‐extraction ability to facilitate charge‐transfer process and restrict charge recombination. In addition, improved water resistance is demonstrated using Cytop, which significantly extends the PSC lifetime (78% of initial PCE vs 22% for control after 1500 h) and increases the practical applicability.