Semitransparent Organic Photovoltaics Utilizing Intrinsic Charge Generation in Non-Fullerene Acceptors.

In organic semiconductors, a donor/acceptor heterojunction is typically required for efficient dissociation of excitons. Using transient absorption spectroscopy to study the dynamics of excited states in non-fullerene acceptors (NFAs), it is shown that NFAs can generate charges without a donor/acceptor interface. This is due to the fact that dielectric solvation provides a driving force sufficient to dissociate the excited state and form the charge-transfer (CT) state. The CT state is further dissociated into free charges at interfaces between polycrystalline regions in neat NFAs. For IEICO-4F, incorporating just 9 wt% donor polymer PTB7-Th in neat films greatly boosts charge generation, enhancing efficient exciton separation into free charges. This property is utilized to fabricate donor-dilute organic photovoltaics (OPV) delivering a power conversion efficiency of 8.3% in the case of opaque devices with a metal top-electrode and an active layer average visible transmittance (AVT) of 75%. It is shown that the intrinsic charge generation in low-bandgap NFAs contributes to the overall photocurrent generation. IEICO-4F-based OPVs with limited PTB7-Th content have high thermal resilience demonstrating little drop in performance over 700 h. PTB7-Th:IEICO-4F semitransparent OPVs are leveraged to fabricate an 8-series connected semitransparent module, demonstrating light-utilization efficiency of 2.2% alongside an AVT of 63%.

A Nonionic Alcohol Soluble Polymer Cathode Interlayer Enables Efficient Organic and Perovskite Solar Cells.

The choice of interfacial materials and their properties play a critical role in determining solar cell performance and stability. For compatibility with roll-to-roll printing, it is desirable to develop stable cathode interface layers (CILs) that can be processed over the photoactive layer using orthogonal solvents. In this study, an n-type naphthalene diimide core and oligo (ethylene glycol) side-chain-based conjugated polymer is reported as a universal, efficient CIL for organic and perovskite photovoltaics. Besides good thermal stability and easy processing in alcohol/water, the new CIL is found to possess electron transport properties with an electrical conductivity of 2.3 × 10-6 S cm-1, enabling its use as a CIL with a film thickness of up to ∼35(±2) nm. Utilizing the new CIL, 16% power conversion efficiency (PCE) is achieved for organic solar cells (OSCs) based on the PM6-Y6 photoactive layer (8.9% PCE for no CIL and 15.1% with state-of-the-art CIL, PDINO), and perovskite solar cells from methylammonium lead iodide yielded a PCE of 17.6%. Compared to the reference devices, the new CIL reduced trap-assisted carrier recombination and increased the built-in potential by 80 mV, simultaneously enhancing all photovoltaic parameters. Moreover, new CIL based devices had better photostability with no burn-in losses.

Efficient tandem solar cells with solution-processed perovskite on textured crystalline silicon.

Stacking solar cells with decreasing band gaps to form tandems presents the possibility of overcoming the single-junction Shockley-Queisser limit in photovoltaics. The rapid development of solution-processed perovskites has brought perovskite single-junction efficiencies >20%. However, this process has yet to enable monolithic integration with industry-relevant textured crystalline silicon solar cells. We report tandems that combine solution-processed micrometer-thick perovskite top cells with fully textured silicon heterojunction bottom cells. To overcome the charge-collection challenges in micrometer-thick perovskites, we enhanced threefold the depletion width at the bases of silicon pyramids. Moreover, by anchoring a self-limiting passivant (1-butanethiol) on the perovskite surfaces, we enhanced the diffusion length and further suppressed phase segregation. These combined enhancements enabled an independently certified power conversion efficiency of 25.7% for perovskite-silicon tandem solar cells. These devices exhibited negligible performance loss after a 400-hour thermal stability test at 85°C and also after 400 hours under maximum power point tracking at 40°C.

Correction: Polymeric hole-transport materials with side-chain redox-active groups for perovskite solar cells with good reproducibility.

Correction for 'Polymeric hole-transport materials with side-chain redox-active groups for perovskite solar cells with good reproducibility' by Rosinda Fuentes Pineda et al., Phys. Chem. Chem. Phys., 2018, 20, 25738-25745.

Polymeric hole-transport materials with side-chain redox-active groups for perovskite solar cells with good reproducibility.

Two monomers, M:OO and M:ON, and their corresponding polymers, P:OO and P:ON, were prepared from styrene derivatives N,N-diphenyl-4-vinyl-aniline with different substituents (-OCH3 and -N(CH3)2) in the N-phenyl para positions. The polymers were synthesised and fully characterised to study their function as hole transport materials (HTMs) in perovskite solar cells (PSCs). The thermal, optical and electrochemical properties and performance of these monomers and polymers as HTMs in PSCs were compared in terms of their structure. The polymers form more stable amorphous glassy states and showed higher thermal stability than the monomers. The different substituent in the para position influenced the highest occupied molecular orbital (HOMO) level, altering the oxidation potential. Both monomers and polymers were employed as HTMs in perovskite solar cells with a device configuration FTO/bl-TiO2/mp-TiO2/CH3NH3PbI3/HTM/Au resulting in power conversion efficiencies of 7.48% for M:OO, 5.14% for P:OO, 5.28% for P:ON and 3.52% for M:ON. Although showing comparatively low efficiencies, the polymers showed much superior reproducibility in comparison with Spiro-OMeTAD or the monomers, suggesting further optimisation of polymeric HTMs with redox side groups is warranted.

Effect of alkyl chain length on the properties of triphenylamine-based hole transport materials and their performance in perovskite solar cells.

A new series of diacetylide-triphenylamine (DATPA) derivatives with five different alkyl chains in the para position, MeO, EtO, nPrO, iPrO and BuO, were synthesised, fully characterised and their function as hole-transport materials in perovskite solar cells (PSC) studied. Their thermal, optical and electrochemical properties were investigated along with their molecular packing and charge transport properties to analyse the influence of different alkyl chains in the solar cell parameters. The shorter alkyl chain facilitates more compact packing structures which enhanced the hole mobilities and reduced recombination. This work suggests that the molecule with the methoxy substituent (MeO) exhibits the best semiconductive properties with a power conversion efficiency of up to 5.63%, an open circuit voltage (Voc) of 0.83 V, a photocurrent density (Jsc) of 10.84 mA cm-2 and a fill factor of 62.3% in perovskite solar cells. Upon replacing the methoxy group with longer alkyl chain substituents without changing the energy levels, there is a decrease in the charge mobility as well as PCE (e.g. 3.29% for BuO-DATPA). The alkyl chain length of semiconductive molecules plays an important role in achieving high performance perovskite solar cells.

Efficient, Semitransparent Neutral-Colored Solar Cells Based on Microstructured Formamidinium Lead Trihalide Perovskite.

Efficient, neutral-colored semitransparent solar cells are of commercial interest for incorporation into the windows and surfaces of buildings and automobiles. Here, we report on semitransparent perovskite solar cells that are both efficient and neutral-colored, even in full working devices. Using the microstructured architecture previously developed, we achieve higher efficiencies by replacing methylammonium lead iodide perovskite with formamidinium lead iodide. Current-voltage hysteresis is also much reduced. Furthermore, we apply a novel transparent cathode to the devices, enabling us to fabricate neutral-colored semitransparent full solar cells for the first time. Such devices demonstrate over 5% power conversion efficiency for average visible transparencies of almost 30%, retaining impressive color-neutrality. This makes these devices the best-performing single-junction neutral-colored semitransparent solar cells to date. These microstructured perovskite solar cells are shown to have a significant advantage over silicon solar cells in terms of performance at high incident angles of sunlight, making them ideal for building integration.

A transparent conductive adhesive laminate electrode for high-efficiency organic-inorganic lead halide perovskite solar cells.

A self-adhesive laminate solar-cell electrode is presented based on a metal grid embedded in a polymer film (x-y conduction) and set in contact with the active layer using a pressure-sensitive adhesive containing a very low quantity (1.8%) of organic conductor, which self-organizes to provide z conduction to the grid. This ITO-free material performs in an identical fashion to evaporated gold in high-efficiency perovskite solar cells.

A one-step low temperature processing route for organolead halide perovskite solar cells.

Organolead trihalide perovskite solar cells based upon the co-deposition of a combined Al2O3-perovskite layer at T < 110 °C are presented. We report an average PCE = 7.2% on a non-sintered Al2O3 scaffold in devices that have been manufactured from a perovskite precursor containing 5 wt% Al2O3 nanoparticles.