Classification of solar cells according to mechanisms of charge separation and charge collection

Abstract

In the last decade, photovoltaics (PV) has experienced an important transformation. Traditional solar cells formed by compact semiconductor layers have been joined by new kinds of cells that are constituted by a complex mixture of organic, inorganic and solid or liquid electrolyte materials, and rely on charge separation at the nanoscale. Recently, metal organic halide perovskites have appeared in the photovoltaic landscape showing large conversion efficiencies, and they may share characteristics of the two former types. In this paper we provide a general description of the photovoltaic mechanisms of the single absorber solar cell types, combining all-inorganic and hybrid and organic cells into a single framework. The operation of the solar cell relies on a number of internal processes that exploit internal charge separation and overall charge collection minimizing recombination. There are two main effects to achieve the required efficiency, first to exploit kinetics at interfaces, favouring the required forward process, and second to take advantage of internal electrical fields caused by a built-in voltage and by the distribution of photogenerated charges. These principles represented by selective contacts, interfaces and the main energy diagram, form a solid base for the discussion of the operation of future types of solar cells. Additional effects based on ferroelectric polarization and ionic drift provide interesting prospects for investigating new PV effects mainly in the perovskite materials.

Implications of Multichromophoric Arrays in Organic Photovoltaics

“…The J-V curves of an ITO/Por+BDP2/C60/BCP//Al device after varying periods of illumination shows how the VOC starts around 0.64V and eventually stabilizes at 0.36 V. 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 to give insight into the molecular D/A pair at the interface of the device when more than one donor or acceptor is present. [53][54][55][56] The BDP-Por devices and the initial scans of the Por+BDP2 devices give V OC values very close to the one observed for an OPV with a neat PtTPBP donor layer, suggesting that the devices have a similar CT state, involving a PtTPBP-C 60 pair at the interface. After illumination the V OC values for the mixed donor Por+BDP2 devices stabilize at 0.36 V, very close to that of the BDP2/C 60 OPV.…”

Origins and mechanisms of hysteresis in organometal halide perovskites

“…In addition, controlled p and n doping induced by an external electrical field [80] allows to further modulate the properties in PSCs. With this approach it is possible to achieve a perovskite PN junction with different doping in different regions [106]. Reprinted with permissions from [78].…”

Simple, Robust, and Going More Efficient: Recent Advance on Electron Transport Layer‐Free Perovskite Solar Cells

“…This is also the view of point that people generally hold in the early stages of PSCs research. [49] Although the ETL/perovskite heterojunction is critical for carrier extraction and device performance, on the one hand, more detailed photoelectron physics studies have shown that perovskite as bipolar semiconductors have large and balanced electron/hole carrier mobility and diffusion length, being capable of transporting both electrons and holes efficiently and simultaneously. For HTL, it can extract the holes from i layer by hole flow or injection with energetic favorable energy level alignment at the i-p interface.…”

“…Charge collection properties are then accessible relying on the relative weight that diffusion and drift have as carrier transport driven forces. [49] Although the ETL/perovskite heterojunction is critical for carrier extraction and device performance, on the one hand, more detailed photoelectron physics studies have shown that perovskite as bipolar semiconductors have large and balanced electron/hole carrier mobility and diffusion length, being capable of transporting both electrons and holes efficiently and simultaneously. [50,51] This means that perovskite itself or some portion of perovskite light absorption layer can serve as both an ETL and an HTL at the same time.…”