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The maximum open-circuit voltage of a solar cell can be evaluated in terms of its ability to emit light. We herein verify the reciprocity relation between the electroluminescence spectrum and subband-gap quantum efficiency spectrum for several photovoltaic technologies at different stages of commercial development, including inorganic, organic, and a type of methyl-ammonium lead-halide CH 3 NH 3 PbI 3−x Cl x perovskite solar cells. Based on the detailed balance theory and reciprocity relations between light emission and light absorption, voltage losses at open circuit are quantified and assigned to specific mechanisms, namely, absorption edge broadening and nonradiative recombination. The voltage loss due to nonradiative recombination is low for inorganic solar cells (0.04-0.21 V), while for organic solar cell devices it is larger but surprisingly uniform, with values of 0.34-0.44 V for a range of material combinations. We show that, in CH 3 NH 3 PbI 3−x Cl x perovskite solar cells that exhibit hysteresis, the loss to nonradiative recombination varies substantially with voltage scan conditions. We then show that for different solar cell technologies there is a roughly linear relation between the power conversion efficiency and the voltage loss due to nonradiative recombination.

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.

Defect passivation and surface modification of hybrid perovskite films are essential to achieving high power conversion efficiency (PCE) and stable perovskite photovoltaics. Here, we demonstrate a facile strategy that combines high PCE with high stability in CH 3 NH 3 PbI 3 (MAPbI 3 ) solar cells. The strategy utilizes inorganic perovskite quantum dots (QDs) to distribute elemental dopants uniformly across the MAPbI 3 film and attach ligands to the film's surface. Compared with pristine MAPbI 3 films, MAPbI 3 films processed with QDs show a reduction in tail states, smaller trap-state density, and an increase in carrier recombination lifetime. This strategy results in reduced voltage losses and an improvement in PCE from 18.3% to 21.5%, which is among the highest efficiencies for MAPbI 3 devices. Ligands introduced with the aid of the QDs render the perovskite film's surface hydrophobic-inhibiting moisture penetration. The devices maintain 80% of their initial PCE under 1-sun continuous illumination for 500 h and show improved thermal stability.

Bifacial monolithic perovskite/silicon tandem solar cells exploit albedo-the diffuse reflected light from the environment-to increase their performance above that of monofacial perovskite/silicon tandems. Here we report bifacial tandems with certified power conversion efficiencies >25% under monofacial AM1.5G 1 sun illumination that reach power-generation densities as high as ~26 mW cm -2 under outdoor testing. We investigated the perovskite bandgap required to attain optimized current matching under a variety of realistic illumination and albedo conditions. We then compared the properties of these bifacial tandems exposed to different albedos and provide energy yield calculations for two locations with different environmental conditions. Finally, we present a comparison of outdoor test fields of monofacial and bifacial perovskite/silicon tandems to demonstrate the added value of tandem bifaciality for locations with albedos of practical relevance.

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.

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transparent conducting contact adhesive that can be applied to perovskite based devices providing conductivity, charge extraction, mechanical adhesion and protection. This has allowed indium-tin oxide (ITO), Au and Ag free entirely non-vacuum processed PSC devices to be fabricated with a solar-to-electrical power conversion effi ciency (PCE) of over 15%.There are some excellent alternatives to replace thermally evaporated silver and gold electrodes in third generation photovoltaic devices, such as solid-state Dye Sensitized Solar Cells (s-DSC) and Organic Photovoltaics (OPV) based on the use of solution processed silver nanowires. [6][7][8] In these situations comparable performance has been achieved to vapor deposited electrodes. Prior to these developments, nanoparticulate silver inks deposited onto the photovoltaic (PV) devices with subsequent heating of the whole device to 150-200 °C were a route to applying the conductor via printing. [ 9 ] This can cause degradation of temperature sensitive components within the devices, such as the hole transporter which is commonly used (Spiro-OMeTAD) with a resultant loss of PV performance. Silver nanowires are advantageous in this respect as the heating step to anneal the nanowires can be conducted separately before being applied onto the devices at room temperature. This is due to the nanowire mesh's low sheet resistance and a good electrical contact made with the cells. [ 6 ] There are however issues with the use of silver based conductors in contact with the PSC since the halide content can give rise to silver halide formation and degradation of performance and we sought a different solution for PSCs.The currently reported high effi ciencies of 12-15% for PSCs have been achieved with a vapor deposited precious metal contact (usually gold). Silver based coatings could suffer from degradation through the formation of silver halides leading to a contact breakdown with the Spiro-OMeTAD. [ 10 ] In order to develop an indium and precious metal free transparent conductor we have combined a corrosion proof Ni mesh electrode (embedded in a PET fi lm) with a silver-free transparent conducting adhesive (TCA). The whole electrode can be fabricated separately to the organic-inorganic lead halide perovskite photoelectrode and then simply laminated at room temperature.The transparent electrode material was obtained from Epigem and is a Ni mesh embedded in a PET fi lm on a roll to roll process; this produces a robust and highly conductive electrode at less than half the cost of ITO PET. The mesh spacing is ca 300 µm, and the PET fi lm with the mesh is 86% transparent and is shown in Figure 1 a. The mesh electrode has extremely A key challenge that can unlock the potential of third generation photovoltaics (PV) is the development of low cost indium free fl exible transparent electrodes to enable lightweight, transparent and metal mounted devices. Here we describe a major breakthrough which allows a highly conducting self-adhesive laminate electrode to be applied to devices at room t...